NRC fire researchers making strides in mid-rise wood research project

Volume 17, Number 4, December 2012

Fire testing for the mid-rise wood building project

Fire researchers at NRC Construction are progressing on a comprehensive project designed to develop fire-safety performance data to facilitate the use of wood-based structural products in mid-rise buildings (see Construction Innovation, March 2012).

With mid-rise buildings currently required to be of non-combustible construction, alternative fire safety solutions are needed before wood-based structural systems can be approved for the same use. (see related story: Changes to allow six-storey wood construction under consideration for national codes)

NRC is working in collaboration with the Canadian Wood Council and FPInnovations and in partnership with Natural Resources Canada and the governments of Ontario, Quebec and British Columbia, where the wood industry occupies a position of great economic significance.

An encapsulation approach

In their efforts to develop solutions to limit the severity and effects of fire in mid-rise, wood-based construction, researchers are evaluating an encapsulation approach. The concept is to encapsulate or cover the wood materials used in the structural assemblies in order to limit their susceptibility to burning in a developing fire. The intention is to provide fire endurance comparable to that of a building made of non-combustible construction. The encapsulation materials selected for the research were gypsum board, cement board and gypsum-concrete.

Following the completion of bench and intermediate-scale experiments to test the concept and establish parameters, researchers planned two large-scale experiments to study the potential of encapsulation in a realistic setting. These experiments feature two different ‘encapsulated’ combustible systems, one a lightweight wood-frame (LWF) system and the other a cross-laminated timber (CLT) system. The large NRC burn hall near Ottawa enabled the construction of an elaborate test set-up of several stories intended to double as a portion of a mid-rise building. The LWF experiment has been completed and the CLT one is in preparation.

Following completion of the CLT experiments, researchers will build another full-scale test to study the fire performance of a code-conforming lightweight steel-frame system for a six-storey building required to be of non-combustible construction. They will then compare the results of this steel-frame experiment to those of the encapsulation projects.

Evaluating fire-safety solutions

Researchers are also evaluating various fire-safety solutions for exterior wall assemblies for use in mid-rise wood buildings. One test arrangement simulated an exterior wall for platform construction using wood studs. The stud cavity was insulated using medium-density spray polyurethane foam while the insulation and combustible framing were protected using gypsum sheathing. A second arrangement simulated an exterior wall system using CLT. The CLT assembly included an outboard insulation system consisting of wood studs and extruded polystyrene in the cavity. The combustible elements of this assembly were also protected using gypsum sheathing.

Both of these exterior wall arrangements met the NBC 2010 requirements to limit fire spread, as tested in accordance with CAN/ULC S134.

Researchers are now conducting a second series of tests on the same two arrangements with the combustible elements protected by fire retardant treated plywood instead of gypsum sheathing.

In their evaluation of these generic exterior wall assemblies for mid-rise buildings, fire researchers are working with NRC building envelope specialists to address NBC Part 5 requirements relating to protection against heat, air, moisture, and precipitation ingress into the envelope.

Using the full-scale wall furnace

In yet another series of tests related to mid-rise construction being conducted in the NRC full-scale wall furnace, researchers are evaluating five generic lightweight wood-frame wall assemblies using standard fire resistance tests. These assemblies, when used on lower floors, are required to have a high load-bearing capacity.

A shear wall assembly will also be tested. These fire resistance tests are being carried out in concert with NRC acoustics researchers to ensure that the assemblies meet sound transmission requirements in addition to the fire resistance requirements.

This extensive wood research program carried out by NRC and its partners will go a long way toward creating opportunities for the use of wood-based structural products in mid-rise construction. The current experimental work is expected to be completed by the spring of 2013. The results will be passed to the Canadian Codes Centre for use in the National Construction Codes.

For more information

Contact Joseph Su at joseph.su@nrc-cnrc.gc.ca or 613-993-9616.