Changes in Parts 3, 4 and 5 of NBC 2015

Volume 20, Number 1

Over 360 proposed changes are incorporated in the National Building Code 2015 (NBC). The changes to Part 9 and those concerned with expanding combustible construction to six storeys are described in separate articles. This article highlights three important sets of changes in Parts 3, 4 and 5.

Updating of accessibility requirements in Part 3

According to the 2012 Canadian Survey on Disability, 14% of Canadians and one in three seniors report having a disability that limits their daily activities. With Canada’s aging population, the demand for accessible facilities in buildings will continue to increase. Code requirements in Section 3.8. are therefore aligned with current knowledge on accessibility and the design improved for accessible routes, doorways, controls and washroom facilities. Design requirements now include the option of complying with CSA-B651, “Accessible Design for the Built Environment.” These changes have little to no cost impact over the NBC 2010 requirements.

New hazard values for seismic design in Part 4 & Appendix C

The seismic hazard values for 679 geographic locations in Appendix C are updated based on recent earthquake data, to provide a better estimate of the actual seismic hazard. In NBC 2010, buildings at locations where the hazard was lower than a threshold value specified in the Code did not require seismic design. This exemption is withdrawn and now all buildings in Canada will be designed for earthquake forces regardless of the level of hazard. A new simplified approach is provided exclusively for low-hazard locations as an alternate to a complex seismic design. Other changes for seismic design requirements in Part 4 include introducing base isolation and supplemental damping systems especially relevant for retrofit projects, new cost-saving provisions for seismic design of large single-storey steel buildings, new requirements for buildings with inclined columns, and requirements to prevent breakage and falling of glass.

New metric for sound transmission in Part 5

Apparent Sound Transmission Class (ASTC) is introduced into Parts 5 and 9 to assess compliance with noise protection requirements between dwelling units. The new metric more accurately captures the sound level perceived by occupants as it also accounts for the noise transmitted through flanking walls, ceilings and floors. It will facilitate design optimization and shift the focus from separating walls, which tend to be over-designed, to the more critical wall-to-wall and wall-to-floor junctions, thereby resulting in more comfortable conditions for occupants and fewer complaints about noise.

The new provision requires a minimum ASTC rating of 47 between dwelling units. Compliance with this rating can be demonstrated by measurements on site, following prescriptive requirements, or by calculation and design. For the third compliance option, designers have at their disposal two publicly available tools; an explanatory guide and the web-application soundPATHS, developed by NRC’s Acoustics Group. The latter tool allows designers to identify areas of overdesign, weak links, and the potential for cost savings.


André Laroche
Telephone: 613-993-9586