Standard fire endurance tests were performed on a full-scale floor assembly and a full-scale wall assembly constructed with cross-laminated timber (CLT) as the main structural element. The full-scale floor assembly consisted of CLT panels encapsulated with fiberglass wool and a single layer of 15.9 mm thick Type X gypsum board on the exposed side and with two layers of 12.7 mm thick cement board on the unexposed side. The full-scale wall assembly was constructed from CLT panels encapsulated with two layers of 15.9 mm thick Type X gypsum board on both faces. Nine thermocouples were installed on the unexposed face of both assemblies to monitor the temperature rise throughout the test and nine deflection gauges were installed on each assembly to monitor deformations. The superimposed load applied on the floor assembly was 9.4 kN/m² and the load imposed on the wall assembly was 449 kN/m. The fire endurance period of the full-scale floor assembly was 128 minutes and that of the full-scale wall assembly 219 minutes. Both the full-scale floor assembly and the full-scale wall assembly failed structurally afterwards under the applied loading. No hose stream tests were carried out on the fullscale floor and wall assemblies.
Recent architectural trends include the design and construction of increasingly tall buildings with structural components comprised of engineered wood referred to by names including; cross laminated timber (CLT), laminated veneer lumber (LVL), or glued laminated timber (Glulam). These buildings are cited for their advantages in sustainability resulting from the use of wood as a renewable construction material. Previous research has shown that timber elements contribute to the fuel load in buildings and can increase the initial fire growth rate – potentially overwhelming fire protection system and creating more severe conditions for occupants, emergency responders, and nearby properties.
The overarching goal of this project Fire Safety Challenges of Tall Wood Buildings Phase 2 (involving five tasks) is to quantify the contribution of CLT building elements (wall and/or floor-ceiling assemblies) in compartment fires and provide data to allow comparison of the performance of CLT systems against other building systems commonly used in tall buildings.
Client Report (National Research Council Canada. Construction)
In early 2018, with funding support from Natural Resources Canada and the Province of Ontario, the National Research Council of Canada conducted a series of room scale fire tests of Encapsulated Mass Timber Construction (EMTC). The goal of this test series is to further quantify the contribution of mass timber elements to fires and provide additional data for forming the technical basis for exposed mass timber elements in EMTC buildings without significantly increasing fire risks to life and property. The goal includes studying the fire performance of the 2nd generation cross-laminated timber (CLT) in resisting char layer fall-off, which could cause fire regrowth in the cooling phase of fully developed fires. The issues of char layer fall-off for the 1st generation CLT panels resulting in fire regrowth during the cooling phase of the fire were clearly revealed in the previous large scale CLT compartment fire tests under the auspices of the Fire Protection Research Foundation.
A research project, Wood and Wood-Hybrid Midrise Buildings, was undertaken to develop information to be used as the basis for alternative/acceptable solutions for mid-rise construction using wood structural elements. As one approach, encapsulation materials could be used to protect the combustible (wood) structural materials for a period of time in order to delay the effects of the fire on the combustible structural elements, including delay of ignition. In delaying ignition, any effects of the combustion of the combustible structural elements on the fire severity can be delayed. In some cases, and depending upon the amount of encapsulating material used (e.g. number of layers), ignition of the elements might be avoided completely. This scenario would primarily depend upon the fire event and the actual fire performance of the encapsulating materials used. The effectiveness of the encapsulation approach in limiting the involvement of wood structural materials in fires was demonstrated in the research project through bench-, intermediate- and full-scale fire experiments.
A research project, Wood and Wood-Hybrid Midrise Buildings, was undertaken to develop information to be used as the basis for alternative/acceptable solutions for mid-rise construction using wood structural elements. The effectiveness of the encapsulation approach in limiting the involvement of wood structural materials in fires was demonstrated in this research project through bench-, intermediate- and full-scale fire experiments. These results for encapsulated lightweight wood-frame (LWF) systems and encapsulated cross-laminated timber (CLT) systems are documented in a series of reports [3, 4, 5, 6].
In addition to developing the encapsulation approach for protecting the wood structural materials to meet the above code intent, research was undertaken to examine standard fire resistance of encapsulated wood structural assemblies for use in mid-rise wood/timber buildings. One of the major differences between structural LWF assemblies used in mid-rise wood buildings (5-6 storeys) and low-rise wood buildings (= 4 stories) is the wall assemblies for the lower storeys. For mid-rise wood buildings, loadbearing wall assemblies on the lower storeys have to be designed to resist higher axial loads due to the self-weight of the upper storeys, which often result in the need for larger-size stud members and/or a greater number of studs, and higher lateral loads in case of seismic events or wind loads, which often requires the use of wood shear panels within the wall assembly. These wall assemblies very often will need to meet standard fire resistance requirements, and therefore, information regarding their standard fire-resistance ratings should be developed. This report documents the results of fullscale furnace tests conducted to develop standard fire-resistance ratings of encapsulated LWF assemblies for use in mid-rise applications.
The acceptable solutions provided in the 2010 National Building Code (NBC) Division B  limits the use of combustible (wood) construction based on building height. For example, for Group C (Residential), Group D (Business and Personal Services) and Group E (Mercantile) occupancies, combustible construction can be used up to 4 storeys, and up to 2 storeys for Group A – Division 2 (Assembly) occupancies. In addition to the building height limitation, there are also building area limitations in the 2010 NBC for the use of combustible construction for these occupancies. For buildings that exceed the height and area requirements for combustible construction, the prescriptive requirements in the 2010 NBC require that noncombustible construction be used for the primary structural elements.
Three materials were selected for investigation as encapsulation materials for combustible structural elements: Type X gypsum board (12.7 mm thick and 15.9 mm thick), cement board (12.7 mm thick) and gypsum-concrete (25 mm thick and 39 mm thick). This report documents the results of intermediate-scale furnace tests conducted to investigate the performance of the three encapsulation materials.