Contrary to concerns over its combustibility,
wood can be an excellent performer under fire conditions. This
is because of wood's unique charring properties, which actually
protect it from fire. Properly designing a building for fire
safety means faithfully executing building code regulations.
For more information about fire endurance, refer to the SPC
Southern
Pine Use Guide.
Framing Around Chimneys and Fireplaces
Wood framing must be adequately separated from fireplace and
chimney masonry. See Figure 5 for fireplace
framing details. All headers, beams, joists, and studs must
be kept at least two inches from the outside face of chimney
and fireplace masonry. Prefabricated metal fireplace and chimney
assemblies must be installed in accordance with the manufacturer's
recommendations and approved by the code authority.
Fireblocking
Fireblocking is an important fire safety feature in wood-framed
buildings with concealed spaces that can serve as ducts or chimneys
for the spread of flames, gases, and smoke. Fireblocking is
an integral part of a building's passive fire protection. Fireblocking
can protect against the passage of flames, deadly gases and
toxic smoke through hollow vertical spaces created by joints
and gaps in walls, floors, and floor/ceiling assemblies. In
short, hollow vertical spaces need to be firestopped at every
floor level.
In light wood-frame construction, 2" dimension lumber has proven
to be very successful in fireblocking if tightly fitted in place.
Codes recognize 2" lumber for use as fireblocks, as well as
wood panels if the joints are backed. For sealing around vents,
pipes, and ducts, the codes permit the code official to approve
other fireblocking materials available in cans, tubes, and strips
for ease of installation. Typically, materials meeting ASTM
E814 Standard Method of Fire Tests for Through-Penetration Firestops
for use with tested commercial firestop systems are acceptable
for fireblocking around ducts and pipes.
Although fireblocking between floors is automatically built
into the framing in most instances, care still needs to be exercised
where certain designs require studs to pass floor levels. The
bottom sill plate of wall framing usually acts as a fireblock.
The use of furring strips, which create horizontal or vertical
concealed spaces, must be fireblocked. For example, in ordinary
construction, the space created when a masonry wall is furred
needs to be fireblocked.
Fireblocking should be installed in these locations:
Concealed spaces of stud walls and partitions, including
furred spaces at ceilings and floor levels.
Concealed spaces between stair stringers at the top and
bottom of the run.
Openings around vents, pipes, ducts, chimneys, and fireplaces
at ceiling and floor levels.
Interconnections between concealed vertical stud wall
or partition spaces and concealed spaces created by an assembly
of floor joists. With respect to concealed spaces created
by an assembly of floor joists, fireblocking should be provided
for the full depth of the joists at the ends and over supports.
