Q: I'm reroofing with red cedar shakes treated with a fire retardant. They have a class C fire rating, the minimum required by state law. We'd like to keep them looking light and new as long as possible. But mostly we just want to preserve them and maintain their fire resistance. Any suggestions?
—Raymond, San Jose, Calif.
A: Tom Silva replies: Just one: Forget about keeping your roof looking like new; wood is going to turn gray no matter what you do. As for fire resistance, do not apply any coating that claims to be a fire retardant. Shingles that are certified as fire-retardant will be permanently protected from fire. As for preserving them, the main thing is to keep the roof clean. An annual sweeping (or blowing) removes pine needles, leaves, and other debris that can accumulate on the roof and trap water against the wood. Pruning overhanging tree branches will help reduce the debris and discourage the growth of moss, another surefire killer of wood roofs. There are any number of products that claim to prolong the life of a cedar roof, and little agreement about their effectiveness. Even the Cedar Shingle & Shake Bureau doesn't come right out and recommend anything. It simply suggests that if you're going to put them on, you should at least enlist the services of a reputable contractor with a solid record locally. According to the bureau, the most suitable products will be formulated specifically for wood roofs, and contain a UV inhibitor, a water repellent, and/or an EPA-registered wood preservative. Before you apply anything, check with the company that made your shakes to be sure it's compatible with the fire retardant.