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Fire Retardant

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Fire Retardent Treated Wood

Learn more information about fire retardant treated wood in the FRTW Labels Guide from Western Wood Preservers Institute. The 2-page overview explains the information found on quality marks for interior and exterior fire retardants, as well as building code references guiding the use of FTRW.

Fire Retardant Treated Wood

Fire Retardant Treated Wood

While wood offers many beneficial features, it also burns when exposed to fire. Fortunately, for some uses the wood can be treated to protect against fire. 

Today's fire-retardant treatments change the chemistry so that when the wood is exposed to fire, non-combustible gas and water vapor are produced so the flames do not advance. In addition, the outside fiber will char and provide an insulating layer that will protect the wood underneath.

Fire retardant treating does not make the wood impervious to fire. However, it does slow the natural progression of flames and smoke caused when wood burns and helps keep structures intact long enough for occupants to exit safely.

Fire retardant treated wood, or FRTW, is available for a variety of uses. Typically, it is used in roof and attics, wall assemblies, stairways, floors, subfloors and interior construction in public areas. Developers and others specify FRTW as an cost-effective alternative to sprinklers.

Building codes guide the use of FRTW in specific applications. Formulations used in fire treating must undergo rigorous fire tests to earn approval under the codes. Review the typical uses for FRTW and corresponding building code references in the publication FRTW Labels and Codes

Like pressure-treated wood, fire retardants are impregnated into the wood to provide lasting protection. There are two types of FRTW products: interior and exterior.


FRTW products treated for interior uses are the most commonly specified materials. Interior FRTW can only be used in areas where there is no significant exposure to water. While used in residential homes, interior FRTW products are typically used in multifamily structures, schools, hospitals and commercial structures that host large public gatherings, including theaters, shopping centers and hotels.

Most interior fire treatments are clear in appearance, so it looks similar to untreated wood. It can be handled safely and can be finished or painted, as long as you follow the manufacturer's recommendations.

The following are the most common interior FRTW brands for interior uses. Click on the links for each for additional information:

Wood that has been fire retardant treated for exterior use combines the durability to withstand outdoor elements while protecting against the advancement of flames and smoke in the event of a fire. Typical uses include storefronts, exterior siding, trim, shakes, shingles, balconies, stairways, canopies and open-air roof systems.

FRTW products treated for exterior uses have undergone extensive testing that replicates the outdoor conditions it may face. For example, one test subjects specimens to the equivalent of more than 800 inches of rain over a 12-week period, followed by fire exposure.

A popular exterior FRTW brand is FRX, made by Lonza Wood Protection.