Design requirements for fire safety are specified in the Building Codes. Fire-resistance ratings,
based on standardized tests, are a measure of the fire resistance of roof and floor assemblies. A
rated roof or floor truss assembly includes the truss members, the floor or roof sheathing on the
upper surface, the ceiling finish on the lower surface and insulation material in the cavity.
Depending on sheathing, ceiling construction, and insulation, truss assemblies have achieved
fire resistance ratings up to 2 hours. Not all truss assemblies require a fire resistance rating. The
building occupancy, the building size, number of exits and the use of sprinklers will determine
what fire resistance rating is required. In some cases additional options may be available when
using fire retardant treated wood. For more information on such products see
Section 10 of the Wood Reference Handbook
outlines the code requirements for fire safety and height and area
potential for buildings making use of light frame trusses. As well, details are provided on how to calculate the
fire-resistance rating of floor and roof assemblies made of plate-connected wood trusses.
One example of a code requirement is the compartmentalization of attic spaces by fire stop material to divide them
into spaces with an area of less than 300 m2 or 20 m in greatest dimension (width/length). To accomplish this an
additional truss sheeted with ½" gypsum board, lumber or 1/2" wood-based panels attached to verticals at 24" o.c.
may be required. If the space is protected by automatic sprinklers, no firestopping is required.
Floor truss assemblies can also be optimized to reduce sound transmission. In apartments,
this limits noises from upper or lower units.
For more detailed information in the U.S consult the fire and Wood Trusses section of the WTCA website or the American Wood Council's publications on fire at http://www.awc.org/Codes/dcaindex.html#FirePubs.
Other items of interest:
CMHC's Best Practice Guide - Fire and Sound Control in Wood Frame, Multi-family Buildings (On the CHMC website, select "Building & Design" then "Highrise & Multi-Unit Design").
CodeCHEK - CodeCHEK is a tool for determining fire safety provisions affecting building construction and requirements for roof assemblies and concealed spaces for Canadian building codes.