See the "Problem" section of the summary for the subject Alteration of Existing Buildings.

The requirements for the energy performance of fenestration, doors or skylights described in Subsection 9.36.2. of Division B of the National Building Code of Canada (NBC) theoretically already apply to the alteration of existing buildings, but the enforcement of the application of Code requirements to alterations and any relaxations depends on the interpretation of the authority having jurisdiction that balances the cost of complying with the Code against the benefits of achieving the Code’s environment objective.

Applying all requirements for the minimum energy performance of fenestration, doors and skylights in Section 9.36. to an alteration, as if the building were newly constructed, could result in alterations that go far beyond their original scope.

However, if voluntary upgrades to fenestration, doors and skylights are not required to achieve at least a reasonable level of energy-efficient performance, an opportunity may be lost to reduce energy use in the existing building (and gain the related cost savings in energy billing).

This proposed change would also potentially save installation costs compared to later upgrades to better products, which would involve reconstructing wall openings and flashing.

This proposed change clarifies the application of the requirements for the energy performance of fenestration, doors and skylights in Article 9.36.2.7. to existing buildings. This proposed change would also facilitate a consistent interpretation of the Code when the costs of compliance are balanced against the benefits of achieving the Code’s environment objective.

This proposed change allows for some relaxation of the requirements when they are applied to existing buildings, which prevents an alteration from going far beyond its original extent. This proposed change also contains sufficient detail for the voluntary alteration of fenestration, doors and skylights.

The costs associated with the replacement of existing windows, doors and skylights with products having higher thermal-resistive characteristics, such as lower U-values and/or higher energy ratings, and related installation were assessed. Using the widely recognized energy-savings estimation software program, RESFEN[1], input parameters were used to calculate the impact of windows on heating and cooling costs for residential houses in different locations (93 U.S. cities), house type (one- or two-storey, new or existing wood-frame or masonry), size (1 700 ft.² for one-storey and 2 600 ft.² for two-storey), foundation type (basement, crawlspace or slab-on-grade) and HVAC system type (gas furnace/electric air conditioning or electric heat pump). The total window area was assumed to be equal to 15% of the total floor area of the house, and the windows were equally distributed in the ordinal directions.

RESFEN allows the type of window to be selected, which was predetermined by the climate zone of the designated city. The annual energy saving cost was calculated for whole-house replacements for the existing types of window to be replaced by windows with a higher energy rating. Types of existing window can be selected from the window library as a built-in pull-down list. The prices for natural gas and electricity were based on the average price in each State in 2013–2014 and 2012–2013, respectively.

This impact analysis assesses the costs and benefits, as applicable, without providing user-specific information, which may differ greatly and add complexity (e.g., opaque/glazed doors, separate consideration on skylights with solar heat gain coefficient, energy rating contribution to heating vs. cooling, heating and cooling degree-days, percentage of fenestration areas to gross wall area ratio).

Calculation Basis

According to National Resources Canada, space heating accounts for 64% of the energy used in the average Canadian house as a result of Canada’s cold climate. Annual average energy use is 130 GJ, which implies 83 GJ is used for annual space heating. Average cooling accounts for 1.6% of the energy used in the average Canadian house. Annual average energy use is 130 GJ, which implies 2 GJ is used for space cooling.

According to the ENERGY STAR guide[2], typical annual energy savings of around 10% and around 30% are expected where replacing double-pane and single-pane windows, respectively, with ENERGY STAR-rated windows, which are typically available for purchase in most climate zones.

It follows that annual average energy savings of 10% represents 8.3 GJ and 0.2 GJ of energy savings in space heating and cooling, respectively, when double-pane windows are replaced with ENERGY STAR-rated windows. The average energy cost in Canada is around $0.179/kWh (1 GJ is 277.79 kWh). With the specified replacement windows, the annual average energy cost savings is expected to be around $412 and $10, respectively. Therefore, the combined total of annual energy cost savings is $422.

It also follows that annual average energy savings of 30% represents 25.5 GJ and 0.6 GJ of energy savings in space heating and cooling, respectively, when single-pane windows are replaced with ENERGY STAR-rated windows. With the specified replacement windows, annual average energy cost savings is expected to be around $1 267 and $30, respectively. Therefore, the combined total of annual energy cost savings is $1 297.

This information is summarized in Table 1.

Table 1. Calculation of Possible Energy Savings with ENERGY STAR-rated Replacement Windows

The average lifespan of residential windows is expected to be more than 20 years. The average cost of 20 new windows, including installation, that are ENERGY STAR-rated and widely available in the market, is around $20 000.

Benefits

This proposed change, linked to the energy objective of the Code, would have benefits that should be expressed in quantitative terms as monetary savings or as incremental annual energy savings.
For this impact analysis, benefits are measurable based on the reduction of both energy costs and total energy consumption associated with replacement windows having higher energy ratings.

References

(1) RESFEN Software, Windows and Daylighting (lbl.gov). https://windows.lbl.gov/resfen-documentation. Note: RESFEN software is free to download; the user’s manual contains complete details on archetypical houses used and other conditions applied when using RESFEN.

(2) National Fenestration Rating Council. Window Savings Estimates. https://www.nfrc.org/windows-doors-skylights/window-savings-estimates/

(3) National Resources Canada. Water heaters. https://natural-resources.canada.ca/energy-efficiency/products/water-heaters/13735

(4) Home Depot. Cost for Replacement Window Installation. https://www.homedepot.ca/en/home/ideas-how-to/windows-doors/window-replacement-cost.html

It is expected that a consistent set of provisions that apply to the alteration of existing buildings would help reduce the administrative and enforcement work of assessing the degree to which any particular requirement could be relaxed without affecting the level of performance of the building with respect to the Code objectives.

This proposed change would aid enforcement by identifying the work necessary to improve the energy performance of an alteration.

Designers, engineers, architects, manufacturers, builders, specification writers and building officials.