Fire-treating cedar shakes

Q: I have a low-cost source for heavy butt #1 red-cedar shakes. Is there some way I can treat the shakes with fire retardant before I apply them? If so, what retardant should I use, and where can I get it?

A: Michael M. Westfall, president of the Cedar Shake & Shingle Bureau, replies: The only permanent fire-treating method that is recognized and approved by building codes (UBC standard 32-7) is the full-cell vacuum-pressure process. Shakes and shingles are locked inside a chamber where a vacuum is created, and fire-retardant chemicals are injected into the innermost layers of the cedar. Several treating companies have been authorized by the Cedar Shake & Shingle Bureau to perform this process. In your area, Cascade Pacific Industries (Jasper Treating Div., P. O. Box 1351, Eugene, Ore. 97440; 800-331-0656) treats shakes using the approved process.

If you’re bent on doing it yourself, the Texas Forest Products Laboratory (P. O. Box 310, Lufkin, Texas 75901) has found that liberal applications of diammonium phosphate (a chemical fertilizer) dissolved in water achieve the UBC’s minimum fire-resistance rating. Unlike the full-cell vacuum-pressure process, this coating is not permanent. If the roof is in a fire-prone area, the researchers recommend monthly applications, especially during the fire season.