Specifying combustible construction in Canada

Heavy timber supports the roof at École de la Vérendrye in Thunder Bay, Ont., also shown at right. Photos courtesy Form Architecture Engineering
Heavy timber supports the roof at École de la Vérendrye in Thunder Bay, Ont. Photos courtesy Form Architecture Engineering

Combustible elements
From an esthetic or constructability standpoint, it is impractical to construct a building entirely of non-combustible material. Taking this into consideration, in structures of non-combustible construction, NBC allows combustible elements such as:

  • millwork;
  • flooring;
  • glazing;
  • electrical outlets;
  • wiring;
  • ductwork;
  • insulation; and
  • partition elements.

While allowing such combustible elements provides some leeway to specifiers and designers, strict definitions preclude use of other combustible elements.

By moving to an objective-based code in 2005, designers and owners were no longer restricted to the ‘one-size-fits-all’ approach of the prescriptive-based code. This allowed for different building arrangements, more cost-effective solutions, and specific site issues to be addressed by means of an ‘alternative solution’ to NBC (Division B, “Acceptable Solutions”).

To include combustible elements in a building of non-combustible construction, which are not specifically permitted by NBC, the Authority Having Jurisdiction (AHJ) often requires an alternative solution application be submitted. This must provide rationale and technical justification in support of the deviation from the acceptable solution.

Non-combustible construction is described in NBC Sentence 3.1.5.1.(1). The objective and functional statements associated with this are:

To limit the probability that fire or explosion will impact areas beyond its point of origin by limiting the severity and effects of fire and explosions and retarding failure of collapse due to the effects of the fire.
To limit the probability of collapse of physical elements due to fire or explosion by retarding failure or collapse due to the effects of fire.

In support of the alternative solution, the applicant must demonstrate the objective and functional statement are satisfied and the proposed alternative solution performs at least “as well as” the acceptable solution.

This two-storey wood-frame school was built using sustainable building practices. The Form design qualifi ed for the Commercial Buildings Incentive Program (CBIP).
This two-storey wood-frame school was built using sustainable building practices. The Form design qualified for the  Commercial Buildings Incentive Program (CBIP).

Alternative solutions are often supported by material testing, in comparison with the acceptable solution, trade literature (i.e. product properties), or other assessments. To justify the inclusion of combustible elements, compliance with the intent of NBC can be demonstrated by a consideration of the following factors:

  • comparison of the flame-spread rating;
  • contribution to the fire load;
  • burning characteristics of the proposed elements when compared to permitted ones;
  • location of the combustible elements (i.e. proximity to other combustible elements); and
  • provision of a sprinkler or other either inherent or voluntary fire safety features.

Essentially, the alternative provides evidence the proposed combustible elements do not increase the risk level acceptable under provisions within NBC.

Current movements within legislation
At national level, a task group of industry experts are currently reviewing potential changes to the 2015 NBC to allow an increase in height and area of buildings of combustible construction.

Provinces are also considering this change. In Ontario, Bill 52, Ontario Forestry Industry Revitalization Act, 2012—currently under consideration by the Legislative Assembly of Ontario—is seeking to make modifications to the 1992 Building Code Act to allow the height of wood-frame structures to increase from four to six storeys. The proposed change reads as follows:

Building code restriction, wood frame buildings:
(1) The building code shall not prohibit a building that is six storeys or less in building height from being of wood-frame construction.
(2) For greater certainty, subsection (1) does not prevent the building code from:
(a) imposing requirements on buildings of wood-frame construction; and
(b) prohibiting specified classes of buildings from being of wood-frame construction.

The proposed bill does not state the building types that will, if passed, be permitted to be wood-frame construction. Additionally, while the bill may be passed, it may take some time for changes to be made to OBC.

Exposed wood was used to create exterior architectural features.
Exposed wood was used to create exterior architectural features.
A wood-frame building during construction.
A wood-frame building during construction.

 

 

 

 

 

 

 

 

 

Future considerations
Historically, constructing buildings of non-combustible materials was the only method to prevent large-scale conflagration. To this day, a major concern with combustible construction is how such structures will perform during a fire. Fire safety features of modern facilities include sprinkler protection, compartmentation, and the use of limited flame-spread materials. These features limit a fire’s ability to grow or spread beyond its area of origin. Structural integrity and fire resistance can be achieved by using:

  • heavy timber (to allow for charring);
  • suitable assemblies;
  • increased density sprinkler systems; and
  • fire-retardant coating or coverings.

To move building regulations forward, and to successfully prepare alternative solutions, one must understand where the individual code requirements originated. Many started as a ‘quick-fix’ measure to address specific concerns within the industry at the time.

With advances in the understanding of fire science and behaviour, fire suppression systems, and fire service capabilities, certain requirements in the code may be outdated and no longer mandated to serve their original purpose. Moving forward with a performance approach allows for the suitability of a construction type to be determined by its quantitative performance in fire—performance based on statistics, testing, and hard data.

Jack Keays-2_ppJack Keays, MSc., P.Eng., is a project engineer at Sereca Larden Muniak Consulting Inc. Based in Toronto, he holds a master’s degree in fire safety engineering from the University of Ulster in Northern Ireland. Keays has more than five years of both national and international experience and is a licensed professional engineer with the Association of Professional Engineers and Geoscientists of British Columbia (APEGBC). He can be contacted via e-mail at jack@lardenmuniak.com.

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