Fire-resistant coating

A fire-resistant coating is a paint, stain or spray applied to wood or another combustible surface to slow how it ignites or how fast flame spreads across it. The word covers several different products: intumescent paints that swell into a char when heated, clear and pigmented fire-retardant coatings, and field-sprayed retardants. What they share is that the treatment sits on the surface, which is why the wildfire codes on this site treat them differently from fire-retardant-treated wood, where the chemical is pressure-driven into the lumber.

What the codes do with it. Where Oregon R327 is adopted, the exterior-wall list is noncombustible, ignition-resistant, heavy timber, log, or an ASTM E2707-tested assembly, with Type X gypsum behind the cladding as a named exception. Coatings are not on that list, and presenters at the 25 June 2026 Central Oregon seminar said coatings are not accepted to meet R327 (siding). The deck walking-surface list in R327.3.5 names tested assemblies, ignition-resistant material, exterior fire-retardant-treated wood and noncombustible material; a coating is none of those. Spray-applied retardant, where a jurisdiction considers it at all, may need a third-party special inspector the jurisdiction has approved (guide). California's OSFM handbook lists siding by model in category 8140 and decking in 8110; no coating appears there as a wall or deck covering.

What a rating on the can means. A coating's flame-spread figure comes from a surface test such as ASTM E84 run on a treated specimen; that is a property of the coated sample, not of your wall, and it is not the extended-run ignition-resistant test R327 names or the ASTM E136 noncombustible test. A coated board is still combustible wood.

Where it can still be useful. As a maintenance product on wood the code does not reach, an existing fence or an outbuilding, a coating does what its test says and no more. It does not change what the first five feet must be made of, and it does not turn a deck or a wall into one of the paths above.