Fire experts get research results in support of the use of encapsulated mass timber exit shafts in mid-rise wood buildings in Québec
In 2015, the National Building Code of Canada introduced prescriptive provisions to allow mid-rise buildings (up to 6-storeys) to be built using combustible construction. These provisions include many features to ensure the safety of occupants and fire fighters in the event of a fire, such as being sprinklered throughout (meeting NFPA 13) and 1-hour fire resistance rated construction assemblies, including floors, roofs, walls, and exit stair shafts. The Ontario Building Code (OBC) and the Québec Construction Code opted to require exit stair shafts in these buildings to be built using noncombustible construction; in addition, the OBC further requires exits meet 1.5-hour fire resistance rating (FRR) requirements.
In 2017, FPInnovations conducted a research project to study the fire safety of mid-rise wood exit shafts. The scope of the project included an investigation into concerns related to the use of wood exits in mid-rise buildings, an analysis of recent Canadian fire statistics in residential multi-family structures, and a fire demonstration of a mass timber wall and supported wood-frame floor. The large-scale fire experiment was intended to demonstrate that a mass timber exit stair wall, for use in a mid-rise building, would be a suitable method of construction to ensure that code objectives and functional requirements are met.
A custom-designed demonstration structure was conducted at National Research Council Canada’s fire research laboratory, where a gypsum protected nail-laminated timber (NLT) wall supported a 1-hour FRR wood-frame I-joist floor assembly. A 2.4 kPa load was applied to the floor and the assemblies were exposed to the CAN/ULC-S101 standard fire.
The floor deflected until failure after 83 minutes. The overall structural fire resistance of the wall was not greatly impacted by either the failure of the floor assembly or charring of the encapsulated NLT wall. The mass timber successfully prevented the passage of smoke and prevented temperature increase on the unexposed side, which simulated the interior of the exit stair. This reaffirms that exits using combustible construction can perform well in a fire by providing sufficient time for occupants to evacuate and fire services to safely perform their operations. This is consistent with the results from the full-scale CLT shaft demonstration fire conducted in 2015 (MFFP Full-Scale Mass Timber Shaft Demonstration Fire – Final Report). FPInnovations is continuing research in 2018-19, funded by BC Forestry Innovation Investment, on the fire resistance of NLT to further improve confidence of the fire performance of mass timber.
This research was directly used as supporting data in a code change request jointly submitted by Cecobois and Technorm Inc to allow exit shafts in mid-rise wood buildings to be built using encapsulated mass timber (combustible) construction with a 1-hour FRR in Québec. The proposal was received favourably by the Régie du bâtiment du Québec (RBQ). Its implementation and construction details are currently under review by Cecobois and the RBQ.