Residential Use

Wood has always been a preferred building material, for many reasons. It is highly workable in the shop or on site; it is both available and renewable; it is relatively inexpensive; and when manufactured into pre-engineered construction components, wood will carry an increased structural load without losing any of its desirable structural properties.

By treating with fire- retardant chemicals, wood will maintain its structural integrity at even higher temperatures than steel, without losing favorable construction properties. And Fire-Retardant Treated Wood (FRTW) maintains its fire retardant properties for the life of the structure.

Thus, pressure treating with a fire retardant chemical allows for expanded use of both dimensional lumber and plywood in the National Building Code, with no sacrifice in design flexibility or good carpentry practices.  In fact, the reverse is true, since the use of FRTW allows the designer greater flexibility in dealing with some of the fire safety aspects of the code where wood is the preferred construction material, or where a potential fire hazard exists.

How FRTW Retards the Spread of Fire

No building is completely fireproof.  However, the inherent integrity of FRTW in fire situations is a major point in its favor, compared to other, non-combustible construction materials.  Intense heat can cause steel beams, girders and trusses to buckle and collapse.  Steel begins to lose strength rapidly: at 550°C it has lost one-half of its breaking strength; at 750°C it has lost 90%.  Most aluminum alloys are even more vulnerable to heat, losing half their original strength at 300°C and melting at 600°C.

Now consider the performance of interior FRTW in the event of fire. The fire retardant chemicals, impregnated into the wood under pressure, begin to react when the temperature approaches 272°C, the point where wood will ignite.  These chemicals convert the wood tars to a carbon char, which in turn acts as a thermal barrier to retard the rate at which the cross-section is reduced by fire.  Non-flammable gases and water vapor are formed and released at a slow, steady rate, to extinguish flammable gas normally produced when wood burns.

FRTW maintains its structural integrity much longer than even non-combustible materials in a fire situation. When the flame source is removed, the treated wood ceases to char, and since it will not support combustion, the flame will not spread.  A further benefit: FRTW does not add to the production of smoke and toxic fumes, the major threats to human life in fire situations.

Produced under Stringent Controls

Fire retardant treated wood is manufactured in Canada by a group of experienced, reputable stable companies who are, in turn, members of Wood Preservation Canada. Their integrity ensures they will fully support the products they offer, and allows them to undertake the rigorous testing required to pass Canada’s building codes and standards.

The National Building Code of Canada (primarily Part 3) requires that all FRTW must be produced through a pressure impregnation method by a licensed treater, in accordance with specific CSA standards; CSA O80.1 Clause 9.9 and CSA O80.2 Clause 9.8. These two standards specify the condition of the material before and after treatment, and specify the UL standard, which determines the product’s performance criteria.  In fact these two standards should be written into a specification, to clarify the type of product to be installed, and to protect the architect against liability should the contractor mistakenly substitute another product such as one surface-treated with fire-retardant paint.

One final condition applies. To ensure its structural stability, all FRTW must be kiln- dried after treatment: lumber to 19% moisture content and plywood to 15% moisture content.

FRTW Passes Flamespread Test

All FRTW used in Canada must have earned the flamespread rating determined under the test know as “CAN4-S102, Standard Method of Test for Surface Burning Characteristics of Building Materials and Assemblies”.  This performance test can be carried out only by an accredited third-party testing agency.  At the same time, a smoke development rating is also assigned to FRTW. After testing, each species of wood is assigned flamespread and smoke development ratings. Ratings are then imprinted on the Underwriter’s Laboratory of Canada label applied to every 100 board feet of FRTW lumber and every 32 square feet of plywood.  Some manufacturers go the extent of coloring the wood to permit clear identification on the job site.