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BUILDING DESIGN Wood-frame housing may be built to various designs and specifications. Whether a standard design is used or a custom design is created, building code provisions and good design principles must be observed to provide a durable house; to maximize occupant health, comfort and safety; and to reduce a building’s environmental footprint. Building design should provide easy access for people of diverse physical capabilities and adapt to occupants’ changing needs. Obtain professional design assistance for special requirements such as barrier-free access for people with disabilities.
STRUCTURAL DESIGN To agree with the National Building Code, the metric spacing of wood framing members is expressed as ‘soft’ conversions from the actual imperial dimensions. For example, spacing of 12, 16 and 24 inches on centre are converted to 300, 400 and 600 mm on centre, respectively. In order to suit the imperial sizes of common 1220 × 2440 mm (4 × 8 ft.) panel products, such as gypsum board, OSB and plywood, the actual spacing of framing members has been adjusted to approximately 305, 406 and 610 mm on centre, respectively. The NBC contains provisions for bracing to resist lateral loads from earthquakes and high winds. The provisions are based on a three-level risk-based approach developed from environmental load data. There are no special requirements for areas where the risk is low to moderate. This means that normal sheathing, cladding and finishes provide adequate resistance. Most of the new requirements apply to areas of high risk, mainly the coastal area of British Columbia. For these areas, builders can incorporate adequate lateral load resistance without the need for further structural engineering design. The measures include providing “braced wall panels” in “braced wall bands” that are
continuous horizontally and vertically throughout the building and that extend from the top of the supporting foundation, slab or subfloor to the underside of the floor or ceiling above. There is also the option of designing in accordance with NBC Part 4 or good engineering practice such as that provided in the Canadian Wood Council’s Engineering Guide for Wood-Frame Construction 2009. Refer to Chapter 10 for more information. In the few Canadian locations where risk is extreme, bracing to resist lateral load must be designed in accordance with NBC Part 4 or good engineering practice such as that provided in the Engineering Guide for Wood-Frame Construction 2009.
FIRE SAFETY The NBC does not explicitly require fire-rated floor or wall assemblies in single-family houses. Wood-frame construction is considered to provide an acceptable level of fire safety, dependent to a degree on gypsum board finishes, which provide essential fire protection of structural components for a certain period of time. In addition, occupants are considered to be familiar with hazards and safety features of such buildings and to know how to safely exit the house. Wood-frame construction can satisfy the fire safety provisions of the National Building Code. Fire safety is a combination of many factors, some of which can be minimized by building requirements, and others that can only be controlled by the occupants. Examples of building code fire safety measures include:
limiting the area of unprotected openings (windows and doors) in buildings close to property lines to reduce the chance of a fire spreading from one house to another; requiring smoke alarms on every floor and in sleeping areas;