Recent wildfires have brought attention to the vulnerability of wood shake roofs and along with it offers of spray-on treatments claiming to make wood roofs fire resistant. The California Fire Chief's Association, Northern California Fire Prevention Officers' Public Education Committee has these answers and recommendations for anyone considering a spray-on treatment.

Will spray-on treatments make untreated wood roofs fire-resistant?
No spray-on application has passed standard tests recognized by the fire and building code industries. Demand copies of test results from recognized laboratories, like Underwriter Laboratories (UL) or recognized building code agencies which will support the seller's claims
Will spray-on treatments produce a class A (the best) flame-spread rating.
Flame-spread ratings and treatments are applicable only to materials used in the interior of buildings. Don't accept applications with flame-spread ratings in place of fire resistant ratings.
Is the material and process approved by the State Fire Marshal?
The State Fire Marshal has not approved any spray-on treatments for roofs. Please notify the State Fire Marshal's office or your local fire department about such claims.
What about a 5-year guarantee?
Guarantees usually do not assure fire resistance but refer to a re-spray if the material fails. Obtain a specific definition of the guarantee. Demand a bond if you are unsure that the company will continue in business.
Will spray-on applications extend the life of wood roofs?
We know of no documented studies to support this claim. Demand to see test results from recognized laboratories.
Do spray-on applications control fungus through the application of a fungicide?
Some do; however, the application of fungicides requires environmental agency approval. Determine if the company has obtained the required permits to apply the toxic materials.
Does the spray-on process include cleaning the roof?
The cleaning process may improve the appearance but can severely damage the roof. Foot traffic cracks the dry shakes and shingles and high water pressure can also damage the roof. Replace combustible wood roofs with approved fire resistant roofing, none of which require re-treatment.