This proposed change updates Appendix C, including Table-C2, to incorporate the effects of climate change.
Related Code Change Request(s):
CCR 1639
Related Proposed Change(s):
PCF 1980, PCF 2018, PCF 2048
Problem
In previous editions of the National Building Code of Canada (NBC) climatic data provided in Table C-2 in Appendix C were based on historical weather observations collected and analyzed by Environment and Climate Change Canada (ECCC). It was assumed that climatic data were time-independent (or stationary). However, in the face of extensive evidence that the climate is changing across Canada, this practice raises real safety concerns for the design of buildings.
To assess the impacts of climate change trends on the climatic data and their associated climatic loads and load combinations specified in the NBC, future climatic data sets have been developed by ECCC [1] based on the current body of research in climate modelling. These models simulate how the climate statistics are likely to change in various regions of Canada between 2024 and 2100 under various greenhouse gas (GHG) emissions scenarios called representative concentration pathways (RCPs). An RCP is a greenhouse gas concentration time profile. Four RCPs were used for the Intergovernmental Panel on Climate Change (IPCC) Fifth Assessment Report (AR5) in 2014: RCP2.6, RCP4.5, RCP6 and RCP8.5 (corresponding to radiative forcing values of 2.6 W/m2, 4.5 W/m2, 6 W/m2 and 8.5 W/m2, respectively, in 2100). These pathways represent different future greenhouse gas concentration time profiles that are possible depending on the volume of greenhouse gases emitted.
There has been international recognition in recent decades that the earth’s climate is changing, with the potential to create higher structural loads and more adverse environmental conditions than currently specified based on historical observations. The consequences of this pose an increased risk to building structural integrity and functionality, and occupant life safety. More frequent high-heat events also increase risk to occupant life safety.
In addition to the need to update NBC Table C-2 to account for climate change effects, it was recognized that the current approach to establishing design wind and snow loads, referred to as the "uniform hazard" approach, does not result in uniform reliability of building performance across the country. In order to harmonize performance expectations of buildings under these load effects, a new methodology is proposed to define the climatic loads, called the "uniform risk" approach, in which the ultimate load is specified directly with an implied load factor of 1.0, similar to current earthquake design practice.
Justification
The results of targeted research conducted by ECCC [1] specifically designed to address the effect of future projections of climatic conditions were accounted for in the update of each parameter of NBC Table C-2. The proposed approach for building design is based on a 50-year time horizon (from 2025 to 2075) and the RCP8.5 future emissions scenario, corresponding to a 2.5°C global warming compared to the 1986-2016 baseline period. The projected future values are applied to the parameters in NBC Table C-2 using the following approach.
For parameters used for structural and building envelope design, such as the effects of snow, rain, wind and moisture, if the projected future value in the 50-year time horizon is greater than the current updated value calculated from historical observations, the projected value is used. If the future value is projected to decrease, the current value is retained. This approach, called the "Minimax Method," assures that over the 50-year time horizon the annual risk of failure does not exceed that which has historically been considered as acceptable. For some variables, such as temperature, the governing case for design may be the minimum, while for others, such as wind and snow, it is the maximum. For instance, for wind, projections mostly show increases in reference pressure in the future, making the last year of service life the governing case; for snow, projections mostly show decreases in snow load in the future, making the first year of service life the worst case. This is deemed an appropriate approach that ensures that the NBC Table C-2 values reflect the maximum loads expected that correspond to the specified annual probability of exceedance.
The non-stationarity of future climate due to the impact of climate change is embedded in NBC Table C-2 using climate change factors derived from regional averages using the Minimax approach [2], [3]. For reference design wind pressures, most areas in Canada have a climate change factor of 1.05, while locations in Ontario, the Atlantic provinces and west of 120°W in British Columbia have a climate change factor of 1.1. For ground snow loads, excepting the northern territories where a climate change factor of 1.05 applies, most regions have a climate change factor of 1.0, as the governing scenario is based on the present climate. The Minimax approach to adopt future values is also applied to the other parameters, using the future change factors from the targeted research results. For some parameters, such as the one-day and 15-minute rainfalls, there are increases at all locations. For the moisture index, future values are applied at locations where the moisture load increases, and the values remain unchanged elsewhere.
In future updates of NBC Table C-2 values, it is expected that current values at that time will be updated to a new baseline period. Projected future values, based on ongoing research, will also be updated and referenced to the same new baseline period. In this way, both the current and future values will be reset to reflect current knowledge at the time of the future update, and the future values using the Minimax Method for this update will not be compounded in future updates.
Terminology is also affected by the effects of a changing climate. Low-probability events have often been described as having a return period which, in a stationary (non-changing) climate, is defined as the average interval in years between such events. The reciprocal of the return period is defined as the annual exceedance probability. For instance, a 50-year return period event has an annual probability of 1/50 or 0.02. In a changing climate, the definition of the return period as an interval between events is not accurate. As a result, low-probability events are now identified with their annual exceedance probability rather than return period, since the annual probability can and often will change over time. For instance, a 50-year return period event is now described as a "1/50 annual probability event," or sometimes just as the "1/50 value."
The uniform risk approach for wind results in a new 1/500 annual probability wind pressure value to reflect the ultimate load. In thunderstorm-prone regions, for wind values at low probabilities such as 1/500, the separate analysis of convective (e.g., thunderstorm) and synoptic (e.g., active low-pressure system with an embedded weather front) wind events generally results in higher wind values than the usual (up to the 2020 edition of the NBC) approach of analyzing the commingled convective and synoptic wind events as a single data set. This effect is not significant at higher annual probabilities, such as 1/10 and 1/50. In addition to future values applied with the Minimax approach, the 500-year wind pressure values also account for the separate analysis of convective and synoptic wind events.
For parameters related to temperature and heating and cooling loads, such as degree-days below 18°C and 15°C, and January and July design temperatures, future values corresponding to a 50-year time horizon and RCP8.5 emissions scenario are applied in a similarly appropriate approach. Since warming is projected to occur for all locations, the current values for degree-day data and January design temperatures are all retained.
Analysis of the energy performance of buildings does not indicate an increased risk of overheating in buildings when cooling systems are provided and sized using historical July temperature data, in the context of a future climate scenario.
However, sizing mechanical cooling systems based on future 50-year July temperature projections could result in oversized cooling equipment, which could increase construction costs. Also, the equipment may never experience the elevated temperature condition during its service life, which is considerably less than 50 years. Oversized cooling equipment can decrease energy efficiency and increase energy costs. The resulting oversizing could make equipment short-cycling worse and lead to inability of the equipment to meet latent loads, resulting in potentially excessive indoor humidity levels. In addition, short-cycling will decrease the service life of equipment. For the purpose of cooling system equipment design, NBC Table C-2 provides July temperature data based on historical observations.
Further work is proposed on the use of future climatic data in energy codes.
Extensive changes to the climatic design data in NBC Table C-2 and related documentation in NBC Appendix C implement the approach described above.
References
[1] Cannon, A.J., Jeong, D.I., Zhang, X., and Zwiers, F. W. Climate-Resilient Buildings and Core Public Infrastructure: An Assessment of the Impact of Climate Change on Climatic Design Data in Canada. Environment and Climate Change Canada, Ottawa, ON, 2020.
[2] Hong, H.P., Tang, Q., Yang, S.C., Cui, X.Z., Cannon, A.J., Lounis, Z., and Irwin, P. Calibration of the design wind load and snow load considering the historical climate statistics and climate change effects. Structural Safety, Vol. 93, 10213, 2021.
[3] Li, S.H., Irwin, P., Lounis, Z., Attar, A., Dale, J., Gibbons, M., and Beaulieu, S. Effects of Nonstationarity of Extreme Wind Speeds and Ground Snow Loads in a Future Canadian Changing Climate. Natural Hazards Review, Vol. 23, No. 4, 04022022, 2022.
PROPOSED CHANGE
Appendix C Climatic and Seismic Information for Building Design in Canada
Footnote: This information is included for explanatory purposes only and does not form part of the requirements.
Introduction
The great diversity of climate in Canada has a considerable effect on the performance of buildings; consequently, building design must reflect this diversity. This Appendix briefly describes how climatic design values are computed and provides recommended design data for a number of cities, towns, and lesser populated680 locations across Canada. Through the use of such data, appropriate allowances can be made for climate variations in different localities of Canada and the National Building Code can be applied nationally.
The climatic design data presented in Table C-2 are based on weather observations collected by the Meteorological Service of Canada, Environment and Climate Change Canada (ECCC), and include the effects of future projections of climatic conditionswhere appropriate. The data were researched and analyzed for the Canadian Commission on Building and Fire CodesCanadian Board for Harmonized Construction Codes by Environment and Climate ChangeCanadaECCC (they also include results from projects by other agencies).
As it is not practical to list values for all municipalitieslocations in Canada, recommended climatic design values for locations not listed can be obtained by e-mail from the Engineering Climate Services Unit of ECCCEnvironment and Climate Change Canada at scg-ecs@ec.gc.ca. It should be noted, however, that these recommended values may differ from the legal requirements set by provincial, territorial or municipal building authorities.
The information on seismic hazard given in this Appendix has been provided by Natural Resources Canada.
General
The choice of climatic elements tabulated in this Appendix and the form in which they are expressed have been dictated largely by the requirements for specific values in several sections of this Code. These elements include ground snow loads, wind pressures, design temperatures, heating degree-days, one-day and 15-minute rainfalls, and annual total precipitation values, and winter average temperatures and wind speeeds. The following notes briefly explain the significance of these particular elements in building design, and indicate which weather observations were used and how they were analyzed to yield the required design values.
Table C-2 lists design weather recommendations and elevations for over 600680 locations, which have been chosen based on a variety of reasons. Many incorporated cities and towns with significant populations are included unless located close to larger cities. For sparsely populated areas, many smaller towns and villages are listed. Other locations have been added to the list when the demand for climatic design recommendations at these sites has been significant. The named locations refer to the specific latitude and longitude defined by the Gazetteer of Canada (Natural Resources Canada), available from Publishing and Depository Services Canadathe Government of Canada Publications Directorate, Public Works and Government Services CanadaPublic Services and Procurement Canada,Ottawa, Ontario K1A 0S5(www.publications.gc.ca). The elevations are given in metres and refer to heights above sea level.
Almost all of the weather observations used in preparing Table C-2 were, of necessity, observed at inhabited locations. To estimate design values for arbitrary locations, the observed or computed values for the weather stations were mapped and interpolated appropriately. Where possible, adjustments have been applied for the influence of elevation and known topographical effects. Such influences include the tendency of cold air to collect in depressions, for precipitation to increase with elevation, and for generally stronger winds near large bodies of water. Elevations have been added to Table C-2 because of their potential to significantly influence climatic design values.
Since interpolation from the values in Table C-2 to other locations may not be valid due to local and other effects, Environment and Climate Change Canada will provide climatic design element recommendations for locations not listed in Table C-2. Local effects are particularly significant in mountainous areas, where the values apply only to populated valleys and not to the mountain slopes and high passes, where very different conditions are known to exist.
Changing and Variable Climates
Climate is not static. At any location, weather and climatic conditions vary from season to season, year to year, and over longer time periods (climate cycles). This has always been the case. In fact, evidence is mounting that the climates of Canada are changing and will continue to change significantly into future. When estimating climatic design loads, this variability can be considered using appropriate statistical analysis, data records spanning sufficient periods, and meteorological judgement. The analysis generally assumes that the past climate will be representative of the future climate.
Past and ongoing modifications to atmospheric chemistry (from greenhouse gas emissions and land use changes) are expected to alter most climatic regimes in the future despite the success of the most ambitious greenhouse gas mitigation plans.(1) Some regions could see an increase in the frequency and intensity of many weather extremes, which will accelerate weathering processes. Consequently, many buildings will need to be designed, maintained and operated to adequately withstand ever changing climatic loads.
Similar to global trends, the last decade in Canada was noted as the warmest in instrumented record. Canada has warmed, on average, at almost twice the rate of the global average increase, while the western Arctic is warming at a rate that is unprecedented over the past 400 years.(1) Mounting evidence from Arctic communities indicates that rapid changes to climate in the North have resulted in melting permafrost and impacts from other climate changes have affected nearly every type of built structure. Furthermore, analyses of Canadian precipitation data shows that many regions of the country have, on average, also been tending towards wetter conditions.(1) In the United States, where the density of climate monitoring stations is greater, a number of studies have found an unambiguous upward trend in the frequency of heavy to extreme precipitation events, with these increases coincident with a general upward trend in the total amount of precipitation. Climate change model results, based on an ensemble of global climate models worldwide, project that future climate warming rates will be greatest in higher latitude countries such as Canada.(2)
The analysis used to estimate the climatic design data for previous editions of the NBC assumed that the past climate would be representative of the future climate. Starting in the 2025 edition, the climatic design data incorporate the effects of future projections of climatic conditions that are based on the current body of research in climate modeling. The models used in the analysis simulate how the climate statistics are likely to change in various regions of Canada from the present to 2100 under various greenhouse gas emissions scenarios called representative concentration pathways (RCPs).
An RCP is a greenhouse gas concentration time profile. Four RCPs were used for the Intergovernmental Panel on Climate Change (IPCC) Fifth Assessment Report in 2014: RCP2.6, RCP4.5, RCP6 and RCP8.5 (corresponding to radiative forcing values of 2.6 W/m2, 4.5 W/m2, 6 W/m2 and 8.5 W/m2, respectively, in 2100). These pathways represent different future greenhouse gas concentration time profiles that are possible depending on the volume of greenhouse gases emitted.
In targeted projects reported by Cannon et al.,(14) Gaur et al.,(15) the Pacific Climate Impacts Consortium,(16) and RWDI,(17)(18) global climate models augmented with nested regional models provided projected future values of the climatic data in Table C-2 for average global warming levels of 0.5°C to 3.5°C, in increments of 0.5°C, relative to a 1986–2016 baseline. The projected future changes to the climatic data were incorporated in a calibration to derive climate change factors reflecting regional averages.(19) The climatic values listed in Table C-2 were obtained by applying the “Minimax” method and a target-reliability-based approach,(19)(20) as described in the following.
For structural design parameters, such as wind and snow loads, the projected future values were determined for an average global warming of 2.5°C over a 50-year time horizon, corresponding to emissions scenario RCP8.5. For locations where an increase is projected, the future value has been applied. For locations where a decrease is projected, the current value has been retained. This approach is deemed appropriate to protect life safety by ensuring that structures are designed to withstand the highest loads for the climatic conditions expected in the 50-year time horizon.
Similarly, for heating- and cooling-related parameters, such as design temperatures and degree-days below 18°C and 15°C, the projected future values were determined for an average global warming of 2.5°C over the same 50-year time horizon, corresponding to emissions scenario RCP8.5. For locations where the heating or cooling load is projected to increase, the future value has been applied. For locations where the load is projected to decrease, the current value has been retained. According to this approach, since warming is projected for all locations in Canada, the current values have been retained for degree-days below 18°C and 15°C and for January design temperatures, whereas projected future changes have been applied to July dry-bulb and wet-bulb design temperatures.
It is expected that, in future editions of the Code, the current values will be updated based on recent observations, reflecting changes that are occurring, and will correspond to the baseline observational period on which the future climate projections will be based. The future climate projections will be updated based on improved climate models developed by the international scientific community, whose results are released periodically by the IPCC, and on improved targeted research on future projections of the climatic design data in the NBC.
January Design Temperatures
A building and its heating system should be designed to maintain the inside temperature at some pre-determined level. To achieve this, it is necessary to know the most severe weather conditions under which the system will be expected to function satisfactorily. Failure to maintain the inside temperature at the pre-determined level will not usually be serious if the temperature drop is not great and if the duration is not long. The outside conditions used for design should, therefore, not be the most severe in many years, but should be the somewhat less severe conditions that are occasionally but not greatly exceeded.
The January design temperatures are based on an analysis of January air temperatures only. Wind and solar radiation also affect the inside temperature of most buildings and may need to be considered for energy-efficient design.
The January design temperature is defined as the lowest temperature at or below which only a certain small percentage of the hourly outside air temperatures in January occur. In the past, a total of 158 stations with records from all or part of the period 1951-66 formed the basis for calculation of the 2.5 and 1% January temperatures. Where necessary, the data were adjusted for consistency. Since most of the temperatures were observed at airports, design values for the core areas of large cities could be 1 or 2°C milder, although the values for the outlying areas are probably about the same as for the airports. No adjustments were made for this urban island heat effect. The design values for the next 20 to 30 years will probably differ from these tabulated values due to year-to-year climate variability and global climate change resulting from the impact of human activities on atmospheric chemistry.
The design temperatures were reviewed and updated using hourly temperature observations from 480 stations for a 25-year period up to 2006 with at least 8 years of complete data. These data are consistent with data shown for Canadian locations in the 2009 Handbook of Fundamentals(3) published by the American Society of Heating, Refrigerating, and Air-Conditioning Engineers (ASHRAE). The most recent 25 years of record were used to provide a balance between accounting for trends in the climate and the sampling variation owing to year-to-year variation. The 1% and 2.5% values used for the design conditions represent percentiles of the cumulative frequency distribution of hourly temperatures and correspond to January temperatures that are colder for 8 and 19 hours, respectively, on average over the long term.
The 2.5% January design temperature is the value ordinarily used in the design of heating systems. In special cases, when the control of inside temperature is more critical, the 1% value may be used. Other temperature-dependent climatic design parameters may be considered for future issueseditions of the Codethis document.
Projected future changes to the January design temperatures, corresponding to an average global warming of 2.5°C, are available. For the locations in Table C-2, the average projected increase in the January design temperatures is about 5°C, with warming projected at all locations. Accordingly, projected future changes have not been applied.
July Design Temperatures
A building and its cooling and dehumidifying system should be designed to maintain the inside temperature and humidity at certain pre-determined levels. To achieve this, it is necessary to know the most severe weather conditions under which the system is expected to function satisfactorily. Failure to maintain the inside temperature and humidity at the pre-determined levels will usually not be serious if the increases in temperature and humidity are not great and the duration is not long. The outside conditions used for design should, therefore, not be the most severe in many years, but should be the somewhat less severe conditions that are occasionally but not greatly exceeded.
The summer design temperatures in this Appendix are based on an analysis of July air temperatures and humidity valueshumidities. Wind and solar radiation also affect the inside temperature of most buildings and may, in some cases, be more important than the outside air temperature. More complete summer and winter design information can be obtained from Environment and Climate Change Canada.
The July design dry-bulb and wet-bulb design temperatures were reviewed and updated using hourly temperature observations from 480 stations for a 25-year period up to 2006. These data are consistent with data shown for Canadian locations in the 2009 Handbook of Fundamentals(3) published by ASHRAE. As with January design temperatures, data from the most recent 25-year period were analyzed to reflect any recent climatic changes or variations. The 2.5% values used for the dry- and wet-bulb design conditions represent percentiles of the cumulative frequency distribution of hourly dry- and wet-bulb temperatures and correspond to July temperatures that are higher for 19 hours on average over the long term.
Projected future changes to the July design temperatures, corresponding to an average global warming of 2.5°C, are available. For the locations in Table C-2, the average projected increase in the July dry-bulb design temperatures is about 4.1°C, with warming projected at all locations. The average projected increase in the July wet-bulb design temperatures is about 3.4°C, with warming projected at all locations. These projected future increases are applied to the “historical” July design temperatures, which were updated based on historical observations, to provide the “future” July design temperatures.
Analysis of the energy performance of buildings does not indicate an increased risk of overheating in buildings when mechanical cooling systems are provided and sized using historical July temperatures in the context of a future climate scenario. However, sizing mechanical cooling systems based on future 50-year July temperature projections could result in oversized cooling equipment, which could increase construction costs. Also, the equipment may never experience the elevated temperature condition during its expected service life, which is considerably less than 50 years.
Oversized cooling equipment could decrease the building's energy efficiency and increase energy costs. The oversizing could also lead to increased short-cycling of equipment and to inability of the equipment to meet latent loads, resulting in potentially excessive indoor humidity levels. In addition, increased short-cycling could decrease the service life of the equipment. Therefore, for the purpose of the design of mechanical cooling system equipment, Table C-2 provides July temperatures based on historical observations.
Heating Degree-Days
The rate of consumption of fuel or energy required to keep the interior of a small building at 21°C when the outside air temperature is below 18°C is roughly proportional to the difference between 18°C and the outside temperature. Wind speed, solar radiation, the extent to which the building is exposed to these elements and the internal heat sources also affect the heat required and may have to be considered for energy-efficient design. For average conditions of wind, radiation, exposure, and internal sources, however, the proportionality with the temperature difference generally still holds.
Since the fuel required is also proportional to the duration of the cold weather, a convenient method of combining these elements of temperature and time is to add the differences between 18°C and the mean temperature for every day in the year when the mean temperature is below 18°C. It is assumed that no heat is required when the mean outside air temperature for the day is 18°C or higher.
Although more sophisticated computer simulations using other forms of weather data have now almost completely replaced degree-day-based calculation methods for estimating annual heating energy consumption, degree-days remain a useful indicator of relative severity of climate and can form the basis for certain climate-related Code requirements.
The degree-days below 18°C were compiled for 1300 stations for the 25-year period ending in 2006. This analysis period is consistent with the one used to derive the design temperatures described above and with the approach used by ASHRAE.(3)
A difference of only one Celsius degree in the mean annual temperature will cause a difference of 250 to 350 in the Celsius degree-days. Since differences of 0.5 of a Celsius degree in the mean annual temperature are quite likely to occur between two stations in the same town, heating degree-days cannot be relied on to an accuracy of less than about 100 degree-days.
Heating degree-day values for the core areas of larger cities can be 200 to 400 degree-days less (warmer) than for the surrounding fringe areas. The observed degree-days, which are based on daily temperature observations, are often most representative of rural settings or the fringe areas of cities.
Projected future changes to the heating degree-day values, corresponding to an average global warming of 2.5°C, are available. For the locations in Table C-2, with warming projected at all locations, the average projected decrease in the degree-days below 18°C values is about 1 100 degree-days. Accordingly, projected future changes have not been applied.
Degree-days below 15°C values, which are useful for building heating calculations, are provided in the 2025 edition of the NBC. These values are based on an ECCC analysis of observations from 1407 stations for the period from 1991 to 2020.
Snow Loads
The roof of a building should be designedable to safely support thesnow loads expected during the building's service lifethe greatest weight of snow that is likely to accumulate on it in many years. Some observations of snow on roofs have been made in Canada, but not enough to form the basis for estimating roof snow loads throughout the country. Similarly, observations of the weight, or water equivalent, of the snow on the ground have not been available in digital form in the past. The observations of roof loads and water equivalents are very useful, as noted below, but the measured depth of snow on the ground is used to provide the basic information for a consistent set of snow loads.
As reported by Newark et al.,(5) in the 1990 to 2020 editions of the NBC,Theestimation of the design snow load on a roof was estimated from snow depth observations using a procedure that involves the following steps:
The depth of snow on the ground, which hashaving an annual probability of exceedance of 1-in-50, is computed.
The appropriate specific weight is selected and used to convert snow depth to loads, Ss.
The load, Sr, which is due to rain falling on the snow, is computed.
Because the accumulation of snow on roofs is often different from that on the ground, adjustments are applied to the ground snow load to provide a design snow load on a roof.
The annual maximum depth of snow on the ground has been assembled for 1618 stations for which data has been recorded by the Meteorological Service of Canada (MSC). The period of record used varied from station to station, ranging from 7 to 38 years. These data were analyzed using a Gumbel extreme value distribution fitted using the method of moments(4) as reported by Newark et al.(5) The resulting values are the snow depths, which have a probability of 1-in-50 of being exceeded in any one year.
The specific weight of old snow generally ranges from 2 to 5 kN/m3, and it is usually assumed in Canada that 1 kN/m3 is the average for new snow. Average specific weights of the seasonal snow pack have been derived for different regions across the country(6) and an appropriate value has been assigned to each weather station. Typically, the values average 2.01 kN/m3 east of the continental divide (except for 2.94 kN/m3 north of the treeline), and range from 2.55 to 4.21 kN/m3 west of the divide. The product of the 1-in-50 snow depth and the average specific weight of the seasonal snow pack at a station is converted to the snow load (SL) in units of kilopascals (kPa).
Except for the mountainous areas of western Canada, the values of the ground snow load at MSC stations were normalized assuming a linear variation of the load above sea level in order to account for the effects of topography. They were then smoothed using an uncertainty-weighted moving-area average in order to minimize the uncertainty due to snow depth sampling errors and site-specific variations. Interpolation from analyzed maps of the smooth normalized values yielded a value for each location in Table C-2, which could then be converted to the listed code values (Ss) by means of an equation in the form:
Ss = smooth normalized SL + bZ
where b is the assumed rate of change of SL with elevation at the location and Z is the location's elevation above mean sea level (MSL). Although they are listed in Table C-2 to the nearest tenth of a kilopascal, values of Ss typically have an uncertainty of about 20%. Areas of sparse data in northern Canada were an exception to this procedure. In these regions, an analysis was made of the basic SL values. The effects of topography, variations due to local climates, and smoothing were all subjectively assessed. The values derived in this fashion were used to modify those derived objectively.
For the mountainous areas of British Columbia, Yukon, and the foothills area of Alberta, a more complex procedure was required to account for the variation of loads with terrain and elevation. Since the MSC observational network often does not have sufficient coverage to detail this variability in mountainous areas, additional snow course observations were obtained from the provincial and territorial governments of British Columbia, Yukon, and Alberta. The additional data allowed detailed local analysis of ground snow loads on a valley-by-valley basis. Similar to other studies, the data indicated that snow loads above a critical or reference level increased according to either a linear or quadratic relation with elevation. The determination of whether the increase with elevation was linear or quadratic, the rate of the increase and the critical or reference elevation were found to be specific to the valley and mountain ranges considered. At valley levels below the critical elevation, the loads generally varied less significantly with elevation. Calculated valley- and range-specific regression relations were then used to describe the increase of load with elevation and to normalize the MSC snow observations to a critical or reference level. These normalized values were smoothed using a weighted moving-average.
Tabulated values cannot be expected to indicate all the local differences in Ss. For this reason, especially in complex terrain areas, values should not be interpolated from Table C-2 for unlisted locations. The values of Ss in the Table apply for the elevation and the latitude and longitude of the location, as defined by the Gazetteer of Canada. Values at other locations can be obtained from Environment and Climate Change Canada.
The heaviest loads frequently occur when the snow is wetted by rain, thus the rain load, Sr, was estimated to the nearest 0.1 kPa and is provided in Table C-2. When values of Sr are added to Ss, this provides a 1/50 annual probability1-in-50-year estimate of the combined ground snow and rain load. The values of Sr are based on an analysis of about 2100 weather station values of the 1/50 annual probability1-in-50-year one-day maximum rain amount. This return periodannual probability value is appropriate because the rain amounts correspond approximately to the joint frequency of occurrence of the one-day rain on maximum snow packs. For the purpose of estimating rain on snow, the individual observed one-day rain amounts were constrained to be less than or equal to the snow pack water equivalent, which was estimated by a snow pack accumulation model reported by Bruce and Clark.(7)
The results from surveys of snow loads on roofs indicate that average roof loads are generally less than loads on the ground. The conditions under which the design snow load on the roof may be taken as a percentage of the ground snow load are given in Subsection 4.1.6. The Code also permits further decreases in design snow loads for steeply sloping roofs, but requires substantial increases for roofs where snow accumulation may be more rapid due to such factors as drifting. Recommended adjustments are given in the "Structural Commentaries (User's Guide – NBC 2020: Part 4 of Division B)".
The ground snow load values, Ss, were updated for the 2015 edition of the Code using a similar approach to the one used for the ground snow load update in the 1990 edition. The Gumbel extreme value distribution was fitted to the annual maxima of daily snow depth observations made at over 1400 weather stations, which were compiled from 1990 onward—to as recently as 2012 for some stations—to calculate the 50-year return period1/50 annual probability snow depth. The 50-year1/50 annual probability ground snow load was then calculated for each weather station by combining the 50-year1/50annual probability snow pack depth with the assigned snow pack density, as described above. The Ss values for each location in Table C-2 were compared with the updated weather station values and revised accordingly. As a result, Ss values remain unchanged for about 84% of the locations, have increased for 11% of the locations, and have decreased for 4% of the locations. The greatest proportion of increases was for locations in the Yukon, Northwest Territories, and Nunavut.
In the 2025 edition of the NBC, the 1/50 annual probability Ss and Sr values are unchanged from the previous edition, except that projected future changes, corresponding to an average global warming of 2.5°C, have been applied using the Minimax approach (i.e., increases have been applied where the projected future values are higher, and the current values have been retained where the projected future values are lower). According to RWDI,(18) the projected future values are lower for locations in southern Canada (the 10 provinces) and higher for locations in northern Canada (Yukon, Northwest Territories and Nunavut) where a future change factor of 1.05 has been applied.
Footnote: Annual probability is now used to describe low-probability events instead of return period, which was frequently used previously. In an unchanging climate, the return period is defined as the average interval, in years, within which a given value occurs or is exceeded. It is the reciprocal of the annual exceedance probability. For instance, a 50-year return period value has a probability of 1/50, or 0.02, of being exceeded in any year. In a changing climate, the interpretation of return period as an average interval is not strictly accurate; rather, the return period is defined only as the reciprocal of the annual exceedance probability, which can change over time. The term “return period” is no longer used to refer to the frequency of certain climate events. The term “annual probability” is now used for this purpose (e.g., “1/50 annual probability” or sometimes “1/50 event” or “1-in-50 event”).
Significantly, in the 2025 edition of the NBC, the 1/1000 annual probability Ss and Sr values are provided to facilitate the change to the “uniform risk” approach, in which the climatic design loads are specified directly at the ultimate load levels. Further details regarding the uniform risk approach can be found in the Commentary entitled Limit States Design in the “Structural Commentaries (User's Guide – NBC 2025: Part 4 of Division B).”
In previous editions of the Code in which the “uniform hazard” approach was used, the calculation of roof snow loads for ultimate limit state design for strength involved applying a load factor of 1.5 to the 1/50 Ss and Sr values for all locations. The application of the 1.5 load factor to the 1/50 annual probability Ss and Sr values results in equivalent 1/1000 annual probability Ss and Sr values. However, the actual 1/1000 values depend on the distribution of the annual maximum values used in the extreme value analysis and vary regionally across Canada, resulting in varying degrees of risk and hence structural reliability.
The uniform risk approach adopted in the 2025 edition uses the actual 1/1000 Ss values calculated using regional data and a load factor reduced to 1.0. As reported by RWDI,(18) the 1/1000 Ss values were calculated using statistical properties of the annual maximum snow depth series used for the most recent snow load update in the 2015 edition. These actual 1/1000 Ss values reflect regional extreme snow characteristics. The 1.5 load factor applied to the 1/50 snow loads is equivalent to a 1.0 factor applied to the actual 1/1000 snow loads, averaged across Canada.
As for the 1/50 annual probability Ss and Sr values, projected future changes, corresponding to an average global warming of of 2.5°C, have been applied to the 1/1000 annual probability Ss and Sr values using the same Minimax approach and future change factors (i.e., 1.05 for Yukon, Northwest Territories and Nunavut).
In the 2025 edition of the NBC, values of the winter average temperature, Tws, and winter average wind speed, Vws, are provided in Table C-2 for use in roof snow drift calculations. The Tws and Vws values are the average dry-bulb temperature and average wind speed (at a height of 10 m in open terrain) when the hourly dry-bulb temperature is lower than 0°C, respectively. These values are based on an ECCC analysis of hourly observations from 592 stations for the period 2014 to 2022. No projected future climate change factors have been applied.
Annual Total Precipitation
Total precipitation is the sum in millimetres of the measured depth of rainwater and the estimated or measured water equivalent of the snow (typically estimated as 0.1 of the measured depth of snow, since the average density of fresh snow is about 0.1 that of water).
The average annual total precipitation amounts in Table C-2 have been interpolated from an analysis of precipitation observations from 1379 stations for the 30-year period from 1961 to 1990.
Projected future changes to the annual average total precipitation values, corresponding to an average global warming of 2.5°C, have been applied. The values for all locations have increased, with an average increase of 12%.
Annual Rainfall
The total amount of rain that normally falls in one year is frequently used as a general indication of the wetness of a climate, and is therefore included in this Appendix. See also Moisture Index below.
Projected future changes to the annual average rainfall values, corresponding to an average global warming of 2.5°C, have been applied. The values for all locations have increased, with an average increase of 22%.
Rainfall Intensity
Roof drainage systems are designed to carry off rainwater from the most intense rainfall that is likely to occur. A certain amount of time is required for the rainwater to flow across and down the roof before it enters the gutter or drainage system. This results in the smoothing out of the most rapid changes in rainfall intensity. The drainage system, therefore, need only cope with the flow of rainwater produced by the average rainfall intensity over a period of a few minutes, which can be called the concentration time.
In Canada, it has been customary to use the 15-minute rainfall that will probably be exceeded on an average of once in 10 years. The concentration time for small roofs is much less than 15 minutes and hence the design intensity will be exceeded more frequently than with a 1/10 annual probability. once in 10 years. The safety factors in the NPC will probably reduce the frequency to a reasonable value and, in addition, the occasional failure of a roof drainage system will not be particularly serious in most cases.
The rainfall intensity values were updated for the 2010 edition of the Code using observations of annual maximum 15-minute rainfall amounts from 485 stations with 10 or more years of record, including data up to 2007 for some stations. Ten-year return periodvValues with a 1/10 annual probability—the 15-minute rainfall having a probability of 1-in-10 of being exceeded in any year—were calculated by fitting the annual maximum values to the Gumbel extreme value distribution(4) using the method of moments. The updated values are compiled from the most recent short-duration rainfall intensity-duration-frequency (IDF) graphs and tables available from Environment and Climate Change Canada.
It is very difficult to estimate the pattern of rainfall intensity in mountainous areas, where precipitation is extremely variable and rainfall intensity can be much greater than in other types of areas. Many of the observations for these areas were taken at locations in valley bottoms or in extensive, fairly level areas.
Projected future changes to the rainfall intensity values, corresponding to an average global warming of 2.5°C, have been applied. The values for all locations have increased, with an average increase of about 29%.
One-Day Rainfall
If for any reason a roof drainage system becomes ineffective, the accumulation of rainwater may be great enough in some cases to cause a significant increase in the load on the roof. In previous editions of this information, it had been common practice to use the maximum one-day rainfall ever observed for estimating the additional load. Since the length of record for weather stations in Canada is quite variable, the maximum one-day rainfall amounts in previous editions often reflected the variable length of record at nearby stations as much as the climatology. As a result, the maximum values often differed greatly within relatively small areas where little difference should be expected. The current values have been standardized to represent the one-day rainfall amounts that have 1 chance in 50 of being exceeded in any one year or the 1-in-50-year return value one-day rainfalls.
The one-day rainfall values were updated using daily rainfall observations from more than 3500 stations with 10 years or more of record, including data up to 2008 for some stations. The 50-year return period values were calculated by fitting the annual maximum one-day rainfall observations to the Gumbel extreme value distribution using the method of moments.(4)
Rainfall frequency observations can vary considerably over time and space. This is especially true for mountainous areas, where elevation effects can be significant. In other areas, small-scale intense storms or local influences can produce significant spatial variability in the data. As a result, the analysis incorporates some spatial smoothing.
Projected future changes to the one-day rainfall values, corresponding to an average global warming of 2.5°C, have been applied. The values for all locations have increased, with an average increase of about 29%.
Determination of Moisture Index (MI)
The relationship between WI and DI to correctly define moisture loading on a wall is not known. The MI values provided in the Table are based on the root mean square values of WI and 1-−DI, with those values equally weighted. This is illustrated in Figure C-1. The resultant MI values are sufficiently consistent with industry's understanding of climate severity with respect to moisture loading as to allow limits to be identified for the purpose of specifying where additional protection from precipitation is required.
Projected future values (based on fractional changes) of moisture index, corresponding to an average global warming of 2.5°C, are available from Gaur et al.(15) For locations where the moisture index is projected to increase (two thirds of the locations), the future value has been applied. For locations where the moisture index is projected to decrease, the current value has been retained.
Figure [C-1] C-1 Derivation of moisture index (MI) based on normalized values for wetting index (WI) and drying index (DI)
Note to Figure C-1:
(1)MI equals the hypotenuse of the triangle defined by WIN and 1-−DIN
Driving Rain Wind Pressure (DRWP)
The presence of rainwater on the face of a building, with or without wind, must be addressed in the design and construction of the building envelope so as to minimize the entry of water into the assembly. Wind pressure on the windward faces of a building will promote the flow of water through any open joints or cracks in the facade.
Driving rain wind pressure (DRWP) is the wind load that is coincident with rain, measured or calculated at a height of 10 m. The values provided in the Table represent the loads for which there is 1 chance in 5 of being reached or exceeded in any one year, or a probability of 20% within any one year. Approximate adjustments for height can be made using the values for Ce given in Sentence 4.1.7.3.(5) as a multiplier.
Because of inaccuracies in developing the DRWP values related to the averaging of extreme wind pressures, the actual heights of recording anemometers, and the use of estimated rather than measured rainfall values, the values are considered to be higher than actual loads.(8)(9) Thus the actual probability of reaching or exceeding the DRWP in a particular location is less than 20% per year and these values can be considered to be conservative.
DRWP can be used to determine the height to which wind will drive rainwater up enclosed vertical conduits. This provides a conservative estimate of the height needed for fins in window extrusions and end dams on flashings to control water ingress. This height can be calculated as:
height of water, mm = DRWP/10, Pa
Note that the pressure difference across the building envelope may be augmented by internal pressures induced in the building interior by the wind. These additional pressures can be estimated using the information provided in the Commentary entitled Wind Load and Effects of the "Structural Commentaries (User's Guide – NBC 2020: Part 4 of Division B)".
Projected future changes to the DRWP values, corresponding to an average global warming of 2.5°C, have been applied. The values for all locations have increased, with an average increase of 9%.
Wind Effects
All structures need to be designed to ensure that the main structural system and all secondary components, such as cladding and appurtenances, will withstand the pressures and suctions caused by the strongest wind likely to blow at that location in many years. Some flexible structures, such as tall buildings, slender towers and bridges, also need to be designed to minimize excessive wind-induced oscillations or vibrations.
At any time, the wind acting upon a structure can be treated as a mean or time-averaged component and as a gust or unsteady component. For a small structure, which is completely enveloped by wind gusts, it is only the peak gust velocity that needs to be considered. For a large structure, the wind gusts are not well correlated over its different parts and the effects of individual gusts become less significant. The "Structural Commentaries (User's Guide – NBC 2020: Part 4 of Division B)" evaluates the mean pressure acting on a structure, provides appropriate adjustments for building height and exposure and for the influence of the surrounding terrain and topography (including wind speed-up for hills), and then incorporates the effects of wind gusts by means of the gust factor, which varies according to the type of structure and the size of the area over which the pressure acts.
The wind speeds and corresponding velocity pressures used in the Code are regionally representative or reference values. The reference wind speeds are nominal one-hour averages of wind speeds representative of the 10 m height in flat open terrain corresponding to Exposure A or open terrain in the terminology of the "Structural Commentaries (User's Guide – NBC 2020: Part 4 of Division B)". The reference wind speeds and wind velocity pressures are based on long-term wind records observed at a large number of weather stations across Canada.
Reference wind velocity pressures in the 1961 to 2005 editions of the Code since 1961 were based mostly on records of hourly averaged wind speeds (i.e. the number of miles of wind passing an anemometer in an hour) from over 100 stations with 10 to 22 years of observations ending in the 1950s. The wind pressure values derived from these measurements represented true hourly wind pressures.
The reference wind velocity pressures were reviewed and updated for the 2010 edition of the Code. The primary data set used for the analysis comprised wind records compiled from about 135 stations with hourly averaged wind speeds and from 465 stations with aviation (one- or two-minute average) speeds or surface weather (ten-minute average) speeds observed once per hour at the top of the hour; the periods of record used ranged from 10 to 54 years. In addition, peak wind gust records from 400 stations with periods of record ranging from 10 to 43 years were used. Peak wind gusts (gust durations of approximately 3 to 7 seconds) were used to supplement the primary once-per-hour observations in the analysis.
Several steps were involved in updating the reference wind values. Where needed, speeds were adjusted to represent the standard anemometer height above ground of 10 m. The data from years when the anemometer at a station was installed on the top of a lighthouse or building were eliminated from the analysis since it is impractical to adjust for the effects of wind flow over the structure. (Most anemometers were moved to 10 m towers by the 1960s.) Wind speeds of the various observation types—hourly averaged, aviation, surface weather and peak wind gust—were adjusted to account for different measure durations to represent a one-hour averaging period and to account for differences in the surface roughness of flat open terrain at observing stations.
The annual maximum wind speed data was fitted to the Gumbel distribution using the method of moments(4) to calculate hourly wind speeds having the annual probability of occurrence of 1-in-10 and 1-in-50 (10-year and 50-year return periods). The values were plotted on maps, then analyzed and abstracted for the locations in Table C-2.
The wind velocity pressures, q, were calculated in Pascals using the following equation:
where ρ is an average air density for the windy months of the year and V is wind speed in metres per second. While air density depends on both air temperature and atmospheric pressure, the density of dry air at 0°C and standard atmospheric pressure of 1.2929 kg/m3 was used as an average value for the wind pressure calculations. As explained by Boyd(10), this value is within 10% of the monthly average air densities for most of Canada in the windy part of the year.
As a result of the updating procedure for the 2010 edition of the Code, the 1-in-50 reference wind velocity pressures remained unchanged for most of the locations listed in Table C-2; both increases and decreases were noted for the remaining locations. Many of the decreases resulted from the fact that anemometers at most of the stations used in the previous analysis were installed on lighthouses, airport hangers and other structures. Wind speeds on the tops of buildings are often much higher compared to those registered by a standard 10 m tower. Eliminating anemometer data recorded on the tops of buildings from the analysis resulted in lower values at several locations.
For the 2020 edition of the Code, the reference wind velocity pressures were updated to reflect the new data collected in the approximately 10 years since the previous update for the 2010 edition. Only data collected at stations with a period of record of at least 20 years were used in the analysis. As a result, the data set comprised wind records from 368 hourly and 222 daily peak wind gust stations with periods of record ranging from 20 to 65 years. The annual maximum wind speed data were fitted to the Gumbel distribution.
The 1-in-50 hourly wind speeds, after adjusting for roughness to represent open exposure, were mapped and compared to the NBC 2015 values for the locations in Table C-2. This updating procedure resulted in small changes to the 1-in-50 reference wind velocity pressures for 60 locations.
The 1-in-10 reference wind velocity pressures were updated using the same procedure, except that regional values of the coefficient of variation were used in the calculations instead of the national value used previously. This procedure resulted in small changes to the 1-in-10 reference wind velocity pressures for 322 locations, including many for which there was no change to the 1-in-50 reference wind velocity pressure.
Wind speeds that have a 1-in-”n” chance of being exceeded in any year, where n < 50, can be calculated from the wind speeds corresponding to the 1-in-10 and 1-in-50 return period values in Table C-2 using the following equation:
Table C-1 has been arranged to give pressures to the nearest one-hundredth of a kPa and their corresponding wind speeds. The value of “q” in kPa is assumed to be equal to 0.00064645 V2, where V is given in m/s.
Significant changes to wind loads are introduced in the 2025 edition of the NBC based on recent work reported by RWDI.(17)(18) As described above for snow loads, a “uniform risk” approach has been developed for wind loads. Since the 1.4 load factor applied to the 1/50 wind pressures is equivalent to a 1.0 factor applied to 1/500 wind pressures, averaged across Canada, the 1/500 wind pressures are now provided in Table C-2. These values were calculated from the NBC 2020 1/10 and 1/50 wind pressure values for each location using the equations above for q (as a function of wind speed and air density) and V1/n, the 1/n annual probability wind speed. The 1/500 wind pressures calculated in this way account for the regional statistical properties of the extreme wind events, a necessary characteristic for the uniform risk approach.
Explicitly expressing extreme wind events at the low annual exceedance probability of 1/500 (i.e., 0.002 or 0.2%) requires accounting for a physical characteristic of extreme winds, as explained below.
In the 2020 and previous editions of the Code, the extreme wind return levels were calculated using the annual maximum observed wind speeds from all wind events, regardless of their cause. There are two common causes of extreme winds in Canada. The most common cause is synoptic wind events corresponding to large mid-latitude low-pressure systems, generally with embedded weather fronts, that result in moderate to high wind speeds, often over extensive areas. Much of Canada is also prone to convective wind events, most commonly associated with thunderstorm and related events, the extremes of which have different statistical characteristics compared to synoptic wind events.
The RWDI project(17) involved separating the annual extremes of wind events by virtue of long-term daily observations of “day with thunderstorm” and of peak gust speed. The annual extremes of the convective and synoptic wind events were analyzed separately, and their respective extreme value frequency distributions were combined using the following equation:
where RS is the annual exceedance probability of synoptic wind events, RC is annual exceedance probability of convective wind events, and RT is the annual exceedance probability of the combined convective and synoptic probability distributions. For thunderstorm-prone regions, the 1/500 wind speed calculated for the combined statistical results is generally higher than the 1/500 event calculated using the single annual maximum series of the commingled synoptic and convective wind events. Note that this effect is not significant for 1/50 events but needs to be accounted for with lower-probability events.
Based on a recent ECCC project using daily thunderstorm and peak gust speed observations, as described above, from 190 stations with at least 10 years of observations for the period from 1955 to 2022, a thunderstorm surcharge factor, TS, was developed to account for this characteristic of extreme wind events. From the correlation between the annual average number of thunderstorm days and the ratio of the 1/500 gust speed for combined data sets compared to commingled data sets, the following TS values (applied to wind pressure) were obtained: 1.1 for locations with more than 20 thunderstorm days per year, 1.05 for locations with 8 to 20 thunderstorm days per year, and 1.0 (i.e., no change) for locations with fewer than 8 thunderstorm days per year. The TS = 1.1 factor applies from southeastern British Columbia, across the southern Prairies, to southern Ontario and Quebec. The TS = 1.05 factor applies from the western British Columbia interior, across the northern portions of the Prairies, Ontario and Quebec, to Atlantic Canada, except Newfoundland and Labrador. The TS = 1.0 factor applies to the outer coasts of Canada and the North. These TS values have only been applied to the 1/500 wind pressure values.
Projected future changes, corresponding to an average global warming of 2.5°C, as recommended by RWDI,(18) have been applied to the 1/10, 1/50, and 1/500 wind pressure values in Table C-2. The projected future changes are all increases, by a factor of either 1.05 or 1.1.
Table [C-2] C-2 Climatic Design Data for Selected Locations in Canada
(1)Environment Canada, Climate Trends and Variation Bulletin: Annual 2007, 2008.
(2)Intergovernmental Panel on Climate Change (IPCC), Climate Change 2007: The Physical Science Basis. Contribution of Working Group I to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change. S. Solomon, D. Qin, M. Manning, Z. Chen, M. Marquis, K.B. Averyt, M. Tignor and H.L. Miller (Eds.). Cambridge University Press, Cambridge, United Kingdom and New York, NY, USA,
996 pp., 2007.
(3)American Society of Heating, Refrigerating, and Air-conditioning Engineers, Handbook of Fundamentals, Chapter 14 – Climatic Design Information, Atlanta, GA, 2009.
(4)Lowery, M.D. and Nash, J.E., A comparison of methods of fitting the double exponential distribution. J. of Hydrology, 10 (3), pp. 259–275, 1970.
(5)Newark, M.J., Welsh, L.E., Morris, R.J. and Dnes, W.V. Revised Ground Snow Loads for the 1990 NBC of Canada. Can. J. Civ. Eng., Vol. 16, No. 3, June 1989.
(6)Newark, M.J. A New Look at Ground Snow Loads in Canada. Proceedings, 41st Eastern Snow Conference, Washington, D.C., Vol. 29, pp. 59-63, 1984.
(7)Bruce, J.P. and Clark, R.H. Introduction to Hydrometeorology. Pergammon Press, London, 1966.
(8)Skerlj, P.F. and Surry, D. A Critical Assessment of the DRWPs Used in CAN/CSA-A440-M90. Tenth International Conference on Wind Engineering, Wind Engineering into the 21st Century, Larsen, Larose & Livesay (eds), 1999 Balkema, Rotterdam, ISBN 90 5809 059 0.
(9)Cornick, S., Chown, G.A., et al. Committee Paper on Defining Climate Regions as a Basis for Specifying Requirements for Precipitation Protection for Walls. Institute for Research in Construction, National Research Council, Ottawa, April 2001.
(10)Boyd, D.W. Variations in Air Density over Canada. National Research Council of Canada, Division of Building Research, Technical Note No. 486, June 1967.
(11)Adams, J., Allen, T., Halchuk, S., and Kolaj, M. Canada's 6th Generation Seismic Hazard Model, as Prepared for the 2020 National Building Code. 12th Canadian Conference on Earthquake Engineering, Québec, QC, paper 192-Mkvp-139, 2019.
(12)Halchuk, S., Allen, T., Adams, J., and Onur, T. Contribution of the Leech River Valley - Devil's Mountain Fault System to Seismic Hazard for Victoria, B.C. 12th Canadian Conference on Earthquake Engineering, Québec, QC, paper 192-WGm8-169, 2019.
(13)Kolaj, M., Allen, T., Mayfield, R., Adams, J., and Halchuk, S. Ground-Motion Models for the 6th Generation Seismic Hazard Model of Canada. 12th Canadian Conference on Earthquake Engineering, Québec, QC, paper 192-hHtH-159, 2019.
(14)Cannon, A.J., Jeong, D.I., Zhang, X., and Zwiers, F. W. Climate-Resilient Buildings and Core Public Infrastructure: An Assessment of the Impact of Climate Change on Climatic Design Data in Canada. Environment and Climate Change Canada, Ottawa, ON, 2020.
(15)Gaur, A., Lu, H., Lacasse, M., Hua, G., and Hill, F. Future projected changes in moisture index over Canada. Building and Environment, Vol. 199, 107923, 2021.
(16)Pacific Climate Impacts Consortium (PCIC). Final Reports for Issues 1, 2 and 3. Prepared for the National Research Council of Canada, Climate-Resilient Buildings and Core Public Infrastructure Initiative. University of Victoria, Victoria, British Columbia, 2001.
(17)RWDI. Climate Change Initiative: Development of Climate Change Provisions for Structural Design of Buildings and Implementation Plan in the National Building Code. Phase 2 – Final Report. Prepared for the National Research Council of Canada, Codes Canada, 2020.
(18)RWDI. Addendum Report: Climate Change Factors for Design Wind Pressures and Ground Snow Loads. Prepared for the National Research Council of Canada, Codes Canada, 2021.
(19)Hong, H.P., Tang, Q., Yang, S.C., Cui, X.Z., Cannon, A.J., Lounis, Z., and Irwin, P. Calibration of the design wind load and snow load considering the historical climate statistics and climate change effects. Structural Safety, Vol. 93, 10213, 2021.
(20)Li, S.H., Irwin, P., Lounis, Z., Attar, A., Dale, J., Gibbons, M., and Beaulieu, S. Effects of Nonstationarity of Extreme Wind Speeds and Ground Snow Loads in a Future Canadian Changing Climate. Natural Hazards Review, Vol. 23, No. 4, 04022022, 2022.
Impact analysis
The following summarizes the updates to the climatic design parameters forming part of NBC Table C-2. The revisions are to account for potential future climate change effects expected over the 50-year design life of buildings and building components.
January 2.5% design temperatures (TJan2.5)
This parameter is used for the design of heating systems in buildings. The values of this parameter are projected to increase for all locations in the future as a consequence of climate warming; therefore, the current historical NBC values are deemed appropriate and are recommended to continue to be used for design. Overall, no change to the NBC 2020 design values of this parameter is proposed.
January 1% design temperatures (TJan1)
This parameter is also used for the design of heating systems in buildings. The values of this parameter are projected to increase for all locations in the future as a consequence of climate warming; therefore, the current historical NBC values are considered appropriate and are recommended to continue to be used for design. Overall, no change to the NBC 2020 design values of this parameter is proposed.
July 2.5% dry temperatures (TJuldry2.5)
This parameter is used for the design of cooling and dehumidifying systems in buildings. The projected values indicate an increase for all locations as a consequence of global warming. Therefore, the NBC 2020 values require updating for climate change effects expected over the design life of 50 years (typical). This updating procedure is expected to result in the following changes in value of this parameter:
Province or Territory
Number of Locations
2°C < ΔTJuldry2.5 ≤ 3°C
3°C < ΔTJuldry2.5 ≤ 4°C
4°C < ΔTJuldry2.5 ≤ 5°C
5°C < ΔTJuldry2.5 ≤ 6°C
6°C < ΔTJuldry2.5 ≤ 7°C
Alberta
55
0
0
7
47
1
British Columbia
108
0
5
21
80
2
Manitoba
24
0
2
22
0
0
New Brunswick
18
0
18
0
0
0
Newfoundland
18
0
17
1
0
0
Nova Scotia
25
0
25
0
0
0
Northwest Territories
17
1
13
3
0
0
Nunavut
16
0
0
15
1
0
Ontario
230
0
229
1
0
0
Prince Edward Island
4
0
4
0
0
0
Quebec
125
0
119
4
2
0
Saskatchewan
31
0
0
19
12
0
Yukon
9
0
5
4
0
0
Total
680
1
437
97
142
3
Across the 680 locations in NBC Table C-2, the projected changes in the values of this parameter over the 50-year future timeframe range from 2.8°C to 6.5°C. A large fraction of the locations (438 out of 680) are projected to have future increases of less than or equal to 4°C, 97 locations are projected to have changes on the order of 4-5°C, 142 locations are projected to have changes on the order of 5-6°C, and 3 locations, in Alberta and British Columbia, are projected to have changes greater than 6°C. To minimize the risk of overheating, and depending on the building location, there will likely be a need for cost-effective solutions to implement fenestration shading systems or advanced fenestration and glazing design, enhanced building envelope design, and a review of the air-handing and cooling system design.
Using a July design temperature based on historical observations for the design of mechanical cooling equipment will
reduce the risk of oversized cooling equipment
maintain energy efficiency and energy costs for cooling
minimize equipment short-cycling and maintain service life of equipment
reduce the risk of excessive indoor humidity levels
July 2.5% wet temperatures (TJulwet2.5)
This parameter is used for the design of cooling and dehumidifying systems in buildings. The values of this parameter are projected to increase at all locations as a consequence of global warming. Accordingly, the NBC 2020 values require updating for climate change effects expected over the design life of typical building cooling and dehumidifying systems (50 years). This updating procedure is expected to result in the following changes in the value of this parameter:
Province or Territory
Number of Locations
1°C < ΔTJulwet2.5 ≤ 2°C
2°C < ΔTJulwet2.5 ≤ 3°C
3°C < ΔTJulwet2.5 ≤ 4°C
4°C < ΔTJulwet2.5 ≤ 5°C
5°C < ΔTJulwet2.5 ≤ 6°C
Alberta
55
0
0
21
34
0
British Columbia
108
0
0
16
92
0
Manitoba
24
0
1
23
0
0
New Brunswick
18
0
0
18
0
0
Newfoundland
18
0
0
18
0
0
Nova Scotia
25
0
5
20
0
0
Northwest Territories
17
0
3
14
0
0
Nunavut
16
0
0
8
8
0
Ontario
230
0
218
12
0
0
Prince Edward Island
4
0
0
4
0
0
Quebec
125
0
106
17
2
0
Saskatchewan
31
0
0
27
4
0
Yukon
9
0
0
9
0
0
Total
680
0
333
207
140
0
Across the 680 locations in NBC Table C-2, the projected changes in the values of this parameter over the 50-year future timeframe range from 2.6°C to 5°C. All locations in Manitoba, New Brunswick, Newfoundland, Nova Scotia, Northwest Territories, Ontario, Prince Edward Island and Yukon are projected to have future increases of less than or equal to 4°C, whereas some locations in Alberta, Nunavut, Quebec and Saskatchewan are projected to have future increases greater than 4°C. To minimize the risk of overheating, there will likely be a need for cost-effective solutions to implement fenestration shading systems or advanced fenestration and glazing design, enhanced building envelope design, and a review of the air-handing and cooling system design.
Using a July design temperature based on historical observations for the design of mechanical cooling equipment will
reduce the risk of oversized cooling equipment
maintain energy efficiency and energy costs for cooling
minimize equipment short-cycling and maintain service life of equipment
reduce the risk of excessive indoor humidity levels
Degree-days below 18°C (HDD18)
This parameter is used to identify the required levels of insulation in the building. The values of this parameter are projected to decrease for all locations in the future as a consequence of climate change; therefore, the current values are deemed appropriate and are recommended to continued to be used for design. Overall, no change in the NBC 2020 design values of this parameter is proposed.
15-minute rain (Rain15)
This parameter is used for the design roof drainage systems. The values of this parameter are projected to increase at all reference locations as a consequence of climate change. Therefore, the design values require updating for climate change effects expected over the design life of buildings (50 years). This updating procedure is expected to result in the following changes in the value of this parameter:
Province or Territory
Number of Locations
ΔRain15≤ 20%
20% < ΔRain15≤ 30%
30% < ΔRain15≤ 40%
40% < ΔRain15≤ 50%
ΔRain15 >50%
Alberta
55
0
55
0
0
0
British Columbia
108
0
104
4
0
0
Manitoba
24
0
3
20
1
0
New Brunswick
18
0
18
0
0
0
Newfoundland
18
0
12
6
0
0
Nova Scotia
25
0
25
0
0
0
Northwest Territories
17
0
0
13
3
1
Nunavut
16
0
0
2
10
4
Ontario
230
0
207
23
0
0
Prince Edward Island
4
0
4
0
0
0
Quebec
125
0
73
49
3
0
Saskatchewan
31
0
18
13
0
0
Yukon
9
0
5
4
0
0
Total
680
0
524
134
17
5
Across the 680 locations in NBC Table C-2, the projected changes in the values of this parameter over the 50-year future timeframe range from 21.8% to 56.1%. A large fraction of the locations (524 out of 680) are projected to have future increases of less than or equal to 30%, whereas, 156 locations are projected to have future increases of 30% or more.
Cost impact on roof drainage systems in the NPC
Refer to "Cost Impact on Roof Drainage Systems in NPC" in the supporting document for PCF 1979 for the full cost analysis. A summary is reproduced here.
The cost impact on roof drainage system requirements per Article 2.4.1.4. in the NPC was determined for three archetypal buildings. The cost increase for upsizing the combined primary and emergency roof drainage systems due to the updated 15-minute rainfall values was calculated. This does not account for the impact of the proposed change on alternative acceptable solutions, such as scuppers. The locations impacted and the cost increase for each archetypal building are as follows:
This parameter is used for design for the accumulation of rainwater on roofs. The values of this parameter are projected to increase at all locations as a consequence of climate change. Therefore, the values require updating for climate change effects expected over the design life of buildings (50 years). This updating procedure is expected to result in following changes in the values of this parameter:
Province or Territory
Number of Locations
ΔRain1day≤ 20%
20% < ΔRain1day≤ 30%
30% < ΔRain1day≤ 40%
40% < ΔRain1day≤ 50%
ΔRain1day >50%
Alberta
55
0
55
0
0
0
British Columbia
108
0
104
4
0
0
Manitoba
24
0
3
20
1
0
New Brunswick
18
0
18
0
0
0
Newfoundland
18
0
12
6
0
0
Nova Scotia
25
0
25
0
0
0
Northwest Territories
17
0
0
13
3
1
Nunavut
16
0
0
2
10
4
Ontario
230
0
207
23
0
0
Prince Edward Island
4
0
4
0
0
0
Quebec
125
0
73
49
3
0
Saskatchewan
31
0
18
13
0
0
Yukon
9
0
5
4
0
0
Total
680
0
524
134
17
5
Across the 680 locations in NBC Table C-2, the projected changes in the value of this parameter over the 50-year future timeframe range from 21.8% to 56.1%. A large fraction of the locations (524 out of 680) are projected to have future increases of less than or equal to 30%, whereas 156 locations are projected to have future increases of 30% or more.
To account for the projected increase in the amount of rain that may fall in a day, and thus to avoid water accumulation and ponding on the roof, the design of the drainage systems would be adjusted, as the value of this parameter would affect the drainage design of flat roofs. The design of the drainage system would need to consider both the number of control flow roof drains and scuppers, and their proper sizing. In the future, there will be a need to design roof areas to drain accumulated water that may result from greater rain loads from the roof.
Moisture index (MI)
This parameter is used to define the minimum levels of protection from precipitation to be provided by cladding assemblies on exterior walls. The following is a summary of the projected changes in values of this parameter as a consequence of climate change over a 50-year horizon, which corresponds to the typical design life of buildings (50 years):
Province or Territory
Number of Locations
ΔMI ≤ -10%
-10% < ΔMI≤ 0
0 < ΔMI≤ 10%
10% < ΔMI≤ 20%
ΔMI>20%
Alberta
55
5
46
4
0
0
British Columbia
108
0
11
52
21
24
Manitoba
24
4
20
0
0
0
New Brunswick
18
0
0
5
13
0
Newfoundland
18
0
0
5
13
0
Nova Scotia
25
0
0
12
13
0
Northwest Territories
17
0
17
0
0
0
Nunavut
16
0
13
3
0
0
Ontario
230
0
63
167
0
0
Prince Edward Island
4
0
0
2
2
0
Quebec
125
0
1
110
14
0
Saskatchewan
31
26
5
0
0
0
Yukon
9
0
7
2
0
0
Total
680
35
183
362
76
24
Across the 680 locations in NBC Table C-2, the projected changes in the values of this parameter over a 50-year future timeframe range from -19.4% to 29.4%. A large fraction of the locations (545 out of 680) are projected to have changes of up to ±10%. A total of 35 locations, located in the prairie provinces of Alberta, Manitoba and Saskatchewan, are projected to have future decreases of greater than 10%, whereas 24 locations, all located in British Columbia, are projected to have future increases of greater than 20%.
The worst-case MI values are recommended for design. This implies that, for locations where future decreases in MI are projected, the current values of MI are recommended for the design of cladding assemblies on exterior walls, whereas for locations where future increases in MI are projected, the future projected values of MI are recommended for design. Overall, 462 locations are projected to have future increases in MI, and 218 locations are projected to have future decreases. Out of the 462 locations projected to have future increases, only 265 locations are associated with projected changes large enough to not be rounded off within one decimal point (the level of accuracy to which MI values are reported in the NBC). Accordingly, the current MI values are updated to increased future projected MI values for these 265 locations and kept unchanged for other locations.
With these changes in MI design values, a cavity between the cladding and the membrane sheathing will be required at 82 additional locations (shown in Figure 1) to minimize the probability of moisture accumulation inboard of the cladding.
Figure 1. Additional locations in NBC Table C-2 that will require a capillary break for protection from potential moisture damage in the building envelope, taking climate change effects into consideration.
Cost impact on NBC Part 9 of updated moisture index values
Refer to "Cost Impact on Part 9 of Updated Moisture Index Values" in the supporting document for PCF 1979 for the full cost analysis. A summary is reproduced here.
The cost impact with respect to NBC Part 9 requirements for termite and decay protection per NBC 9.3.2.9.(3)(b) was determined for the 56 locations with a moisture index moving from less than or equal to 1 to greater than 1 due to the updated moisture index values. The locations impacted and the cost increases for a sample wood deck using preservative-treated instead of untreated lumber are as follows:
Northern
BC
AB
Prairies
ON
QC
Atlantic
National
NT
NU
YT
SK
MB
NB
PE
NS
NL
Total locations impacted
0
0
0
4
0
0
0
2
37
8
2
0
3
56
Cost difference per deck ($)
n/a
n/a
n/a
289.20
n/a
n/a
n/a
271.91
435.24
444.62
444.62
n/a
544.17
415.89
The cost impact with respect to NBC Part 9 requirements for minimum protection from precipitation ingress per NBC Sentence 9.27.2.2.(5) was determined for the 53 new locations that will require a capillary break between the first and second planes of protection due to the updated moisture index values. The material and installation costs for vertical strapping between the cladding and sheathing to provide a capillary break were calculated for an archetypal house. The locations impacted and the cost increase per unit are as follows:
Northern
BC
AB
Prairies
ON
QC
Atlantic
National
NT
NU
YT
SK
MB
NB
PE
NS
NL
Total locations impacted
0
0
0
1
0
0
0
2
37
8
2
0
3
53
Cost per unit ($)
n/a
n/a
n/a
1706
n/a
n/a
n/a
1666
1653
1226
1226
n/a
1520
1391
Driving rain wind pressure (DRWP)
This parameter is used for the design of wall assemblies to help ensure that incidental water entry into the assembly is minimized and for the selection of fenestration products. The following is a summary of the projected changes in the values of this parameter as a consequence of climate change over the typical design life of buildings (50 years):
Province or Territory
Number of Locations
ΔDRWP≤ -5%
-5% < ΔDRWP≤ 0
0 < ΔDRWP≤ 5%
5% < ΔDRWP≤ 10%
ΔDRWP>10%
Alberta
55
0
3
23
21
8
British Columbia
108
0
0
0
42
66
Manitoba
24
0
4
3
12
5
New Brunswick
18
0
0
2
10
6
Newfoundland
18
0
0
5
7
6
Nova Scotia
25
0
1
13
10
1
Northwest Territories
17
0
0
2
6
9
Nunavut
16
0
0
0
2
14
Ontario
230
0
16
35
169
10
Prince Edward Island
4
0
0
1
1
2
Quebec
125
0
14
43
53
15
Saskatchewan
31
1
5
12
11
2
Yukon
9
0
0
0
0
9
Total
680
1
43
139
344
153
Across the 680 locations in NBC Table C-2, the projected changes in the values of this parameter over a 50-year future timeframe range from -5.4% to 17.8%. A large fraction of the locations (636 out of 680) are projected to have future increases in DRWP, whereas 44 locations are projected to have future decreases. Out of the 636 locations projected to have future increases, 548 locations are projected to have changes large enough to not be rounded off within zero decimal places (the level of accuracy to which DRWP values are reported in the NBC). Accordingly, the current DRWP values are updated to increased future projected values for these 548 locations, for the design of wall assemblies and selection of fenestration products, and the current DRWP values are retained for the other locations. The design to ensure the watertightness of waterproofing systems around windows and doors would also need to account for the change in DRWP at locations where the increase is larger than 10% (i.e., for 153 locations).
Cost impact on NBC Part 9 of updated DRWP values
Refer to "Cost Impact on Part 9 of Updated Driving Rain Wind Pressure (DRWP) values" in the supporting document for PCF 1979 for the full cost analysis. A summary is reproduced here.
The cost impact with respect to NBC Part 9 requirements for flashing installation per NBC Clause 9.27.3.8.(4)(c) was determined for 74 locations where the required end-dam height will be increased due to the updated DRWP values. The cost increase of extending the end-dam height of window flashing was calculated for an archetypal house. The locations impacted and the cost increase per unit are as follows:
The following is a summary of changes projected in the values of this parameter as a consequence of climate change over the typical design life of buildings (50 years):
Province or Territory
Number of Locations
ΔQ10 ≤ 0%
0% < ΔQ10 ≤ 5%
5% < ΔQ10 ≤ 10%
10% < ΔQ10 ≤ 15%
ΔQ10>15%
Alberta
55
0
26
29
0
0
British Columbia
108
0
15
48
45
0
Manitoba
24
0
10
14
0
0
New Brunswick
18
0
0
4
14
0
Newfoundland
18
0
0
8
10
0
Nova Scotia
25
0
0
11
14
0
Northwest Territories
17
0
5
12
0
0
Nunavut
16
0
11
5
0
0
Ontario
230
0
0
92
138
0
Prince Edward Island
4
0
0
2
2
0
Quebec
125
0
63
62
0
0
Saskatchewan
31
0
9
22
0
0
Yukon
9
0
9
0
0
0
Total
680
0
148
309
223
0
Across the 680 locations in NBC Table C-2, the projected changes in the values of this parameter over a 50-year future timeframe range from 3.5% to 12%. Since all locations are projected to have future increases in Q10, these increased values are applied as the future projected values. The 1-in-10 reference wind velocity pressure, Q10, is used for the determination of the wind-induced accelerations of buildings for serviceability (see the Commentary entitled Wind Load and Effects in the "Structural Commentaries (User's Guide – NBC 2020: Part 4 of Division B)"). The climate change factor for Q10 is similar to that for Q500 (and Q50); modest increases in building accelerations can be expected. Except for very tall buildings, acceptable accelerations will probably still be obtained without a significant change to structural design. For tall buildings that are very dynamically sensitive, the increase in Q10 may result in some additional structural costs to comply with serviceability criteria with respect to acceleration. Very dynamically sensitive tall buildings are required to be assessed through testing in a wind tunnel, which often allows significant optimization of the structure to be achieved.
1/50 hourly wind pressure (Q50)
The following is a summary of the changes projected in the values of this parameter as a consequence of climate change over the typical design life of buildings (50 years):
Province or Territory
Number of Locations
ΔQ50 ≤ 0%
0% < ΔQ50 ≤ 5%
5% < ΔQ50 ≤ 10%
10% < ΔQ50 ≤ 15%
ΔQ50>15%
Alberta
55
0
55
0
0
0
British Columbia
108
0
23
85
0
0
Manitoba
24
0
24
0
0
0
New Brunswick
18
0
0
18
0
0
Newfoundland
18
0
0
18
0
0
Nova Scotia
25
0
0
25
0
0
Northwest Territories
17
0
17
0
0
0
Nunavut
16
0
16
0
0
0
Ontario
230
0
0
230
0
0
Prince Edward Island
4
0
0
4
0
0
Quebec
125
0
125
0
0
0
Saskatchewan
31
0
31
0
0
0
Yukon
9
0
9
0
0
0
Total
680
0
300
380
0
0
Across the 680 locations in NBC Table C-2, the projected changes in the values of this parameter over a 50-year future timeframe range from 5% to 10%. Since all locations are projected to have future increases in Q50, the increased values are applied as the future projected values. Where the increases are higher than 5%, the total deflection of the building may be affected in terms of serviceability and comfort; therefore, the design of the building would need to be verified with respect to increased wind loads and, where warranted, the stiffness of building structural systems would need to be increased to ensure compliance with the serviceability requirements in the NBC 2025. As well, the design of cladding and roofing systems would need to account for increased strength of their connections. The locations where there are increases in reference wind velocity pressure would likely have increases to the cost of the building structure of less than 5%. This, in turn, would increase the total construction cost by less than 0.5%. Considering that these projected cost increases would be more than offset by improved safety and the prevention of wind-related failures, such cost increases are entirely reasonable.
Cost impact on NBC Part 9 of updated 1/50 hourly wind pressure
Refer to "Cost impact of climatic load changes on Part 9: Future projected climate data for snow and wind loads (PCF 1979)" in the supporting document for PCF 1979 for the full cost analysis. A summary is reproduced here.
For structural sufficiency of glass (NBC Sentence 9.6.1.3.(2)), a 128.5 m2, 2-storey detached home, which contained five differently sized windows with glass areas between 0.57 m2 and 1.43 m2, was used as the archetype. In 649 of the 680 locations in NBC Table C-2, the 1-in-50 hourly wind pressures remained below the maximum limits provided in NBC Tables 9.6.1.3.-A, 9.6.1.3.-B and 9.6.1.3.-C before and after the change, resulting in no impact. In 3 of the 31 locations with a potential impact—Cowley, AB; Cape Race, NL; and Resolution Island, NU—the 1-in-50 hourly wind pressure before and after the proposed change exceeded the maximum value of 1.0 kPa provided in the prescriptive table in the NBC; this would require consultation with the window manufacturer for glass thickness and would likely have a cost impact. For the remaining 28 locations, there would be an increased cost for windows of $126.98 to $353.51.
For nailing of framing (nailing of roof trusses, rafters and joists to wall framing; NBC Sentence 9.23.3.4.(3)), a 120 m2 bungalow was used as the archetype. Due to the proposed change, 6 new locations—Argentia, NL; Channel-Port aux Basques, NL; Grand Bank, NL; St. John's, NL; Wabana, NL; and Nottingham Island, NU—will have 1-in-50 hourly wind pressures that are equal to or exceed 0.8 kPa, and roof trusses, rafters or joists would be required to be tied to wall framing with connectors that can resist 3kN of roof uplift. For 6 these locations, the number of galvanized steel connectors required was calculated to be approximately 72, resulting in a cost increase of $437.04.
For fasteners for sheathing (NBC Article 9.23.3.5.), a 128.5 m2, 2-storey detached house was used as the archetype. In 667 of the 680 locations in NBC Table C-2, the 1-in-50 hourly wind pressures remained below 0.8 kPa, resulting in no impact. Seven of the 13 remaining locations already have a 1-in-50 hourly wind pressure greater than 0.8 kPa in the current NBC Table C-2, resulting in no impact. The same 6 locations noted above will have 1-in-50 hourly wind pressures that exceed 0.8 kPa due to the proposed change, resulting in the following impacts:
For roof sheathing, the 6 new locations would require larger fasteners and fasteners spaced at 50 mm within 1 m of the roof edge. The cost increase using common wire nails was estimated to be $468.68 for each location.
For wall sheathing, the 6 new locations would require braced wall panels with wood-based wall sheathing, resulting in a cost increase of $1,125.30 for each location.
For anchorage of building frames (NBC Sentence 9.23.6.1.(3)), the same 6 new locations noted above will have 1-in-50 hourly wind pressures that exceed 0.8 kPa, resulting in an increase in the number of anchor bolts by 15 for a total cost increase of $94.20.
For required roof sheathing (NBC Sentence 9.23.16.1.(1)), a 128.5 m2 2-storey detached bungalow was used as the archetype. The same 6 locations noted above would be impacted by the proposed change and be required to meet Subsection 9.23.16. The cost increase for going from a sheathing deemed too thin for truss spacing in NBC Sentence 9.23.16.7.(2) to a compliant plywood sheathing was approximately $168.82.
For lumber roof sheathing (NBC Article 9.23.16.5.), the roof area of a 128.5 m2 2-storey detached house was used as the archetype. The same 6 locations noted above would be impacted by the proposed change and be required to have lumber roof sheathing installed diagonally instead of horizontally, per NBC Sentence 9.23.16.5., resulting in a cost increase of approximately $311.67 for each location.
For the attachment of cladding to flat insulating concrete form (ICF) wall units (NBC Sentence 9.27.5.4.(2)), a 128.5 m2 2-storey detached house was used as the archetype. In 612 of the 680 locations in NBC Table C-2, the 1-in-50 hourly wind pressure is equal to or less than 0.6 kPa before and after the proposed change, resulting in no impact. In 34 of the remaining 68 locations, the 1-in-50 hourly wind pressure is greater than 0.6 kPa before and after the proposed change, so the impact is assumed to be minimal and would account for additional fasteners. The greatest impact would be experienced where the 1-in-50 hourly wind pressure increases from equal to or less than 0.60 kPa to more than 0.6 kPa after the proposed change, which occurs in the remaining 34 locations. This resulted in an approximate cost increase of $2,009.15 in these locations, representing the different material costs for fasteners into concrete, the additional labour, and the reduced daily output to attach the furring through the flat ICF wall units into the solid concrete back-up wall.
1/50 snow load Ss (Ss50)
The following is a summary of the changes projected in the values of this parameter as a consequence of climate change over the typical design life of buildings (50 years):
Province or Territory
Number of Locations
ΔSs50< 0%
ΔSs50= 0%
0% < ΔSs50≤ 2%
2% < ΔSs50< 5%
ΔSs50=5%
Alberta
55
0
55
0
0
0
British Columbia
108
0
108
0
0
0
Manitoba
24
0
24
0
0
0
New Brunswick
18
0
18
0
0
0
Newfoundland
18
0
18
0
0
0
Nova Scotia
25
0
25
0
0
0
Northwest Territories
17
0
0
0
0
17
Nunavut
16
0
0
0
0
16
Ontario
230
0
230
0
0
0
Prince Edward Island
4
0
4
0
0
0
Quebec
125
0
125
0
0
0
Saskatchewan
31
0
31
0
0
0
Yukon
9
0
0
0
0
9
Total
680
0
638
0
0
42
Across the 680 locations in NBC Table C-2, the projected changes in the values of this parameter over a 50-year future timeframe range from 0% to 5%. All 638 locations in the provinces of Alberta, British Columbia, Manitoba, New Brunswick, Newfoundland, Nova Scotia, Ontario, Prince Edward Island, Quebec and Saskatchewan are projected to have no change in Ss50 in the future; accordingly, the design values for these locations remain the same as the current values. For the remaining 42 locations in the Northwest Territories, Nunavut and Yukon, a future increase in snow loads of 5% is projected and, as such, the future projected values are the recommended design values for those locations. Although the projected increase in snow loading in the North is greater than 4%, it is anticipated that this proposed change will have a negligible effect on total building costs in the future.
1/50 snow load Sr (Sr50)
The following is a summary of the changes projected in the values of this parameter as a consequence of climate change over the typical design life of buildings (50 years):
Province or Territory
Number of Locations
ΔSr50< 0%
ΔSr50= 0%
0% < ΔSr50≤ 2%
2% < ΔSr50< 5%
ΔSr50=5%
Alberta
55
0
55
0
0
0
British Columbia
108
0
108
0
0
0
Manitoba
24
0
24
0
0
0
New Brunswick
18
0
18
0
0
0
Newfoundland
18
0
18
0
0
0
Nova Scotia
25
0
25
0
0
0
Northwest Territories
17
0
0
0
0
17
Nunavut
16
0
0
0
0
16
Ontario
230
0
230
0
0
0
Prince Edward Island
4
0
4
0
0
0
Quebec
125
0
125
0
0
0
Saskatchewan
31
0
31
0
0
0
Yukon
9
0
0
0
0
9
Total
680
0
638
0
0
42
Across the 680 locations in NBC Table C-2, the projected changes in the values of this parameter over a 50-year future timeframe range from 0% to 5%. All 638 locations in the provinces of Alberta, British Columbia, Manitoba, New Brunswick, Newfoundland, Nova Scotia, Ontario, Prince Edward Island, Quebec and Saskatchewan are projected to have no change in Sr50 in the future; accordingly, the design values for these locations remain the same as the current values. For the remaining 42 locations in the Northwest Territories, Nunavut and Yukon, a future increase in snow loads of 5% is projected and, as such, the future projected values are the recommended design values for those locations. Although the projected increase in snow loading in the North is higher than 4%, it is anticipated that this proposed change will have a negligible effect on total building costs in the future.
Cost impact on NBC Part 9 of updated 1/50 snow loads
Refer to "Cost impact of climatic load changes on Part 9: Future projected climate data for snow and wind loads (PCF 1979)" in the supporting document for PCF 1979 for the full cost analysis. A summary is reproduced here.
For platforms subject to snow and occupancy loads (NBC Sentence 9.4.2.3.(1)), a 3.5 m by 4 m exterior platform was assessed as the archetype. Of the 42 locations impacted by the updated 1/50 snow loads, 29 locations had specified snow loads less than 1.9 kPa before and after the proposed change, resulting in no impact. Of the 13 remaining locations, 6 locations had specified snow loads that remained within the same range before and after the proposed change, resulting in no impact. Of the 7 remaining locations, using the archetype, span tables, and costs from RSMeans, only 2 locations had a cost increase—$47.77 in Tungsten, NT, and $126.43 in Kugluktuk/Coppermine, NU.
For performance of windows, doors and skylights (NBC Sentence 9.7.3.1.(2)), the magnitude of the cost impact could not be determined without industry knowledge of the structural design of skylights, including the capacity of the skylight frames and glazing.
For columns (NBC Sub 9.17.1.1.(1)(b)(ii)), a 2.44 m by 4 m exterior platform that is raised 3 m from the ground by 3 columns was assessed. In 41 of the 42 locations impacted by the updated 1/50 snow loads, the sum of the specified snow load and the occupancy load remained below 4.8 kPa before and after the proposed change, resulting in no impact. It was found that there was no change in cost in the last location—Resolution Island, NU—as the same column size was applicable before and after the change.
For ridge support (NBC Sentence 9.23.14.8.(5) and NBC Table 9.23.14.8.), a 120 m2 bungalow was used as the archetype. In 32 of the 42 locations impacted by the updated 1/50 snow loads, the specified snow load remained within the same range before and after the proposed change, resulting in no impact. Of the 10 remaining locations, 3 were not impacted because the same number of nails were sufficient before and after the proposed change. In the 7 remaining locations, the maximum number of additional nails required was 3 nails, resulting in an additional material cost of $5.45 in Eureka, NU.
For ICF lintels (NBC Sentence 9.20.17.4.(3) and NBC Span Tables 9.20.17.4.-A, 9.20.17.4.-B and 9.20.17.4.-C), an approximately 120 m2 bungalow was used as the archetype, assuming 150 mm thick ICF walls. ICF lintel sizes before and after the proposed change were analyzed where the ground snow load exceeded 3.33 kPa. In 31 of the 42 locations impacted by the updated 1/50 snow loads, the ICF lintel size was sufficient to support the snow load before and after the proposed change, resulting in no impact. In Resolution Island, NU, the ground snow load exceeded both those listed in the NBC span tables and those provided by an ICF manufacturer and will likely require a structural engineer to design using NBC Part 4 with additional material and labour costs. For the 10 remaining locations in the Yukon, Northwest Territories and Nunavut, there was an increased cost for ICF lintels of $6.71 to $32.63.
For spans for joists, rafters and beams (NBC Sentence 9.23.4.2.(1)), an approximately 120 m2 bungalow was used as the archetype. In 38 of the 42 locations impacted by the updated 1/50 snow loads, the specified snow load before and after the proposed change remained within the same range, resulting in no impact. The impacts on the remaining 4 locations—Fort Smith, NT; Tungsten, NT; Eureka, NU; and, Kugluktuk, NU—are as follows:
For roof joists (NBC Span Tables 9.23.4.2.-D and 9.23.4.2.-E), there was no impact in Fort Smith, NT, and Tungsten, NT, because the same roof joist size was sufficient before and after the proposed change. The cost increase in Eureka, NU, and Kugluktuk, NU, was approximately $1,850.00.
For roof rafters (NBC Span Tables 9.23.4.2.-F and 9.23.4.2.-G), there was no impact in Kugluktuk, NU because the size of the roof rafters was sufficient before and after the proposed change. There was a cost increase of $255.30 to $1,342.89 in the 3 remaining locations.
For built-up ridge beams and lintels supporting the roof (NBC Span Table 9.23.4.2.-L), there was no impact in Tungsten, NT, because the size of the built-up ridge beam was sufficient before and after the proposed change. There was a cost increase of $140.24 to $262.66 in the 3 remaining locations.
For lintels of various wood species (NBC Span Tables 9.23.12.3.-A, 9.23.12.3.-B, 9.23.12.3.-C and 9.23.12.3.-D), there was a cost increase in all 4 locations of $32.13 to $84.47.
Uniform hazard vs. uniform risk
The introduction of new data for snow and wind loads reflects a change in the approach used to assess reliability in NBC Part 4 from "uniform hazard" to "uniform risk":
New specified wind and snow load values are proposed that reflect a uniform risk by reducing the current load factors of 1.4 and 1.5, respectively, to 1.0 and by using 500-year recurrence wind loads and 1000-year recurrence snow loads.
New parameters, winter average temperature and wind speed, are introduced (for snow drifting calculations on roofs).
The impacts of these changes are addressed in PCF 1980, which incorporates proposed climate-related changes in NBC Part 4, including the uniform risk approach.
Most importantly, this new approach will provide a more uniform level of safety across the country, depending on the site-specific climate, that accounts for climate projections over a 50-year horizon but keeps the same target level of safety (currently, a probability of failure of 0.001 during the 50-year assumed service life). In addition, this will harmonize the approach used for climatic loads with the approach used for seismic effects (2475-year recurrence of design earthquake).
Overall, the proposed changes to NBC Table C-2 will result in buildings with a lower risk of failure during their entire service compared to past practice. While the changes in some locations may seem significant, the proposed approach remains reasonably simple and is not disruptive to the current practice.
In most cases, it is expected that common construction methods, material spacings and design considerations would prove to be resilient enough that no significant additional measures or costs would be needed to satisfy the engineering design resulting from the shift to the proposed uniform risk approach and climate change factors.
Enforcement implications
There are no foreseeable enforcement implications.
Who is affected
Designers, architects, building regulators and building owners.
