Archived – Public Review on Proposed Changes to the National Model Codes — Fall 2009

Care Occupancies (NBC Part 3 and Part 9; Appendix Note in Division A)

Some of the proposed changes originally submitted to the fall 2008 public review have been revised in light of the comments received and are now being resubmitted for public review in 2009. They deal with issues such as corridor widths for wheelchairs and stretchers, construction requirements for buildings up to 3 storeys in building height, and hold-open devices for doors.

Climbable Guards (NBC Part 3 and Part 9)

These proposed changes represent a compromise solution that respects both industry concerns (i.e. sales of various configurations of guards) and regulatory authority concerns (i.e. child safety). Design limitations are being removed for certain applications, such as in homes (where it is assumed that parents monitor children), and in other types of occupancies, such as bars and prisons (where children are absent); design specifications for other applications are being replaced with a simple statement that the guards cannot be climbable. The proposed changes leave it up to the authority having jurisdiction to determine whether a guard is climbable or not.

Protection Against Falls from Residential Occupancy Windows (NBC Part 3)

Concerns from various advocacy groups, coupled with recent incidents of children falling through openable residential occupancy windows, prompted the development of this technical change to the NBC. As part of the overall initiative to harmonize Parts 3 and 9, it was noted that protection against falls from such windows was not addressed in Part 3. The proposed change introduces window opening protection requirements by way of a guard or mechanism to control the window opening to not more than 100 mm.

Protection Against Radon Ingress (NBC Part 5, Part 6 and Part 9)

In June 2007 when Health Canada published the new guideline for indoor radon concentration, which establishes an annual average concentration of 200 Bq/m³, there was widespread acknowledgement by industry and the Canadian public that the lower limit was justified. It was also generally expected that the National Building Code would reference the new guideline. Because the current NBC requirements are written based on the previous limit of 800 Bq/m³, it was not clear whether buildings constructed according to those requirements would provide acceptable levels of protection relative to the 200 Bq/m³ limit.

The Joint Task Group on Protection Against Radon Ingress reviewed the NBC Part 5, 6 and 9 requirements related to soil gas control in light of the new Health Canada guideline and discussed whether the applicable provisions:

• are adequate to protect occupants from the ingress of radon in the context of the lower concentration limit specified in the guideline
• provide viable compliance options for builders and designers, and
• are clear enough for designers, builders and building officials.

Measures on how to provide protection for occupants in buildings (Part 5 and Part 6) as well as in housing and small buildings (Part 9) were developed based on health impact statistics provided by Health Canada and based on acceptable solutions for radon mitigation provided by CMHC. Through a small data acquisition study in new homes situated in three locations across Canada known to have a radon problem, the Joint Task Group established that the proposed changes would minimize the ingress of radon in the context of the lower annual average concentration limit specified in the guideline and that they would facilitate radon mitigation, should the need arise. And so, the resulting proposed NBC requirements address the new Health Canada radon guideline, which states: "The construction of new dwellings should employ techniques that will minimize radon entry and will facilitate post-construction radon removal, should this subsequently prove necessary."

The Task Group members reached consensus to reference the 200 Bq/m³ limit in the appendix rather than the body of the Code because of the difficulty to enforce this limit at the time of construction.

Fall 2009 Public Review
The Standing Committee on Environmental Separation (NBC Part 5) is proposing to insert a performance target related to radon to the requirements for air leakage so as to prompt designers to consider the occurrence of radon when designing the air barrier system at assemblies in contact with the ground.

The Standing Committee on Building and Plumbing Services (NBC Part 6) is proposing to reference a good engineering practice document on how to mitigate the effect of a potentially high concentration of radon in buildings.

The Standing Committee on Housing and Small Buildings (NBC Part 9) is proposing prescriptive measures on how to provide the rough-in for future radon mitigation systems in all buildings to which Part 9 applies.

Revisions to Table C-2 of Appendix C of NBC Division B

The revisions to Table C-2 presented for review are the result of three separate initiatives: the update of the climatic data, an examination of the localities for which there are entries in Table C-2 and an improvement to the equation derived to fit the seismic observational data. Each initiative is explained in more detail below.

Update of Climatic Data
The climatic data in Table C-2 have not been seriously re-analyzed and updated for many years. In the case of wind loads, for example, the vast majority of the reference wind pressures have not changed since the 1960s. The accuracy of the statistical analysis of wind, or any other climatic parameter, can be greatly improved with the addition of another 30 or 40 years of data. An update of this data is necessary to maintain the currency of design in Canada. The work on updating the data is now underway and has been completed for the hourly wind pressures and heating degree-days. This material is presented for information purposes only, and is shown as changes to the hourly wind pressure and heating degree-day values.

Localities
The sites for which the climatic and seismic data are presented in Table C-2 have been reviewed and it is proposed to revise the locations as follows:

• add new locations to facilitate determination of seismicity for designers
• delete locations that do not correspond to the name of the locality noted in Table C-2 or where there is no town at the location (only 2 sites are affected)
• shift some established locations to better suit representative values for seismic and climatic data in that municipality (the shift of locations does not impact the climatic data; only the seismic values are affected).

Seismic Data
The basis for seismic data for structural design was revised from the zonal values used in the 1995 NBC to site-specific spectral acceleration values in the NBC 2005 generated by a quadratic equation to fit the observational data. An 8-parameter relationship has been derived that produces a better fit across all zones, particularly in lower earthquake zones in eastern Canada. It is proposed to use that improved 8-parameter relationship in the seismic data presented in the NBC 2010. The 2010 values differ on average from the 2005 ones approximately as follows:

• geotechnical design levels (based on PGA values) are reduced by 30%
• the design forces for short period buildings are reduced by 20%, and
• the design forces for tall buildings are increased by 30%.

Since zones of low seismicity cover a large part of the country, the climatic information for about 550 of the 650 localities listed in Table C-2 has changed (often in a minor way); only some western localities are unaffected.

Care Occupancies (NFC Part 2)

Some of the proposed changes originally submitted to the fall 2008 public review have been revised in light of the comments received and are now being resubmitted for public review in 2009. They deal with issues such as corridor widths for wheelchairs and stretchers, construction requirements for buildings up to 3 storeys in building height, and hold-open devices for doors.