An engineer or architect is required when the design of a building falls outside the prescriptive provisions of Part 9 of the National Building Code, and for certain occupancies that exceed three storeys in building height or 600 m2 in building area. Building area is defined as the greatest horizontal area of a building above grade within the outside surface of exterior walls. Building height is defined as the number of storeys contained between the roof and the floor of the first storey.
The occupancies permitted to be constructed within Part 9 of the code, if they do not exceed three storeys in building height or 600 m2, are as follows:
- Residential (Group C)
- Business and Personal Services (Group D)
- Mercantile (Group E)
- Medium-Hazard Industrial (Group F, Division 2)
- Low-Hazard Industrial (Group F, Division 3)
Energy efficiency requirements from Section 9.36 of the National Building Code can be used for any of the above occupancies if their building area does not exceed 300 m2. If this limit is exceeded, the energy requirements must be designed by an engineer using the National Energy Code of Canada for Buildings, NECB 2017.
Although these occupancies are permitted to be constructed under Part 9, if any of the proposed construction falls outside the prescriptive provisions provided, those portions of the construction must be designed by an engineer of architect. Some common examples of this are as follows:
- Foundation walls with backfill height that exceeds the values in Table 9.15.4.2.-A of the NBC 2015.
- Foundation walls that are not provided lateral support at the top (i.e., foundation walls at a stairwell with no floor system on top), foundation wall openings greater than 1.2 m wide, or when the total width of all openings constitutes more than 25% of the total length of the wall as per Article 9.15.4.3. of the NBC 2015.
- Pile and grade-beam foundations with living space above. Although there are no provisions for piles in Section 9.15. of the NBC, local experience has proven over time that these foundations, commonly used for garages, are an acceptable solution. These foundations are commonly used for garages. When these foundations support living space above the garage, an engineer is required to design the foundation to ensure occupant safety.
- Preserved wood foundations that fall outside the prescriptive provisions of the CSA S406-14 standard.
- Wood-frame walls with a height that exceeds the values provided in Table 9.23.10.1. of the NBC 2015.
- Any structural member with a span exceeding 12.2 m, when individual framing members are spaced more than 600 mm apart, and when the specified live load on supported subfloors and floor framing exceeds 2.4 kPa as per Article 9.23.1.1. of the NBC 2015.
- Tempered glass that is used as a guard and is not provided with a top rail. An engineer must confirm the glass can withstand the forces required for guards in Table 9.8.8.2. of the NBC 2015.
- Buildings that fall outside the scope of Part 9 are buildings that exceed three storeys in building area or 600 m2 in building area, or fall under the occupancies listed below:
Assembly (Group A)
Detention (Group B, Division 1)
Treatment (Group B, Division 2)
Care (Group B, Division 3)
High-Hazard Industrial (Group F, Division 1)
These buildings and all building systems require professional designer involvement to ensure compliance with the requirements of Part 3 (Fire Protection, Occupant Safety, and Accessibility), Part 4 (Structural Design), Part 5 (Environmental Separation), and Part 6 (Heating, Ventilating, and Air-Conditioning). These buildings also require a professional designer to ensure compliance with the energy code, NECB 2017.
A building code analysis is required at the discretion of the building official for these types of projects. It provides valuable information related to the project such as:
- Occupancy classification and design
- Building area and height
- The number of streets the building faces
- Fire-resistance ratings for floor, wall, and roof assemblies
- Occupant loading and travel distances
- Construction types, etc.