Non-combustible, as applied to an elementary building material, means such material has been tested and found to comply with the relevant provisions of CSA B54.1-1960. The current standard for testing non-combustible construction is Underwriters Laboratories of Canada (ULC) CAN 4-S114, Standard Method of Test for Determination of Non-combustibility in Building Materials. While the test standard has changed, the definition and intent in the current code is primarily the same as the 1965 definition.
Building height restriction can be traced back to the height where a fire-hose stream could reach when fighting a fire from the structure’s exterior. The height of combustible construction was also limited due to any increased fuel load in the building, or anticipated issues associated with additional fuel load and potential fire spread within the facility.
Up until 1990, a residential building of combustible construction was not permitted to exceed three storeys in height. That year, however, the code recognized the benefits of sprinkler protection in controlling fires, as well as limiting the resultant smoke and heat. This paved the way for residential building height to increase to four storeys, provided a sprinkler system was installed throughout.
At a provincial level, the British Columbia Building Code (BCBC) was amended in 2009 to allow residential buildings of combustible construction to increase from four to six storeys. This change came after a review of potential risks and mitigating features, and after exploring how mid-rise wood construction has been regulated in other jurisdictions. (For more on wood buildings, see “Mid-rise Makeovers: B.C. Code Changes Encourage Building with Wood,” by Jim Taggart, Dip. Arch., MA, MRAIC, and “The Sky’s the Limit: Designing Airports with Wood,” by Eric Karsh, M.Eng., P.Eng., Struct.Eng., MIStructE, Ing., in the September 2012 issue of Construction Canada. )
Building area restriction was originally intended to control a fire’s size by limiting the amount of combustible contents in a floor area. This constraint was due to concerns with how the facilities performed in fire and increased fuel load. Before the 1941 NBC, the area of buildings of combustible construction was regulated by municipal building departments and local bylaws. As NBC evolved, the maximum area permitted for a structure of combustible construction has increased, and the current code permits a residential building of four storeys high to have an area up to 1800 m2 (19,375 sf) when there are sprinklers throughout.
Increases in building area have been associated with the introduction of sprinkler protection. However, this author feels the rationale behind permitting expanded areas has largely been arbitrary and opinion-based as opposed to statistics or analysis.