Ask the Carpenter: How to keep algae off your roof

Ask the Expert Home Improvement

Q. I am replacing my roof, and because of past algae problems, I asked the contractor if he could install a zinc strip just below the ridge line to prevent algae formation. He said there are new shingles (GAF Timberline) that have an element embedded in them that will do the same thing as the zinc strip. He said roofers have been using that type of shingle rather than the zinc strip since 2012. I have never heard you or the late Peter Hotton (who wrote the Handyman on Call and Ask the Handyman columns) refer to this as a remedy. Is this the common practice now?


A. The GAF Timberline has a feature called StainGuard protection. StainGuard is a specially formulated granule that inhibits algae growth. Other than that, I don’t know much about them, having heard about them only a few years ago. To me, it’s too soon to tell; five years old is still a new roof, and it is unclear how long it would take algae to form. You could ask the roofer for references from clients who have had this roof installed.


Q. We have a medicine cabinet with a mirrored front in our master bathroom. The edges of the mirrored surface are worn away in the back, so you see an ugly, uneven, and dark surface instead of the mirror in the front. Is there any way to fix this without replacing the medicine cabinet? If we can’t fix the mirror, is there any way to paint a stripe or put on a decorative decal/sticker to hide the defect?


A. Can you remove the mirror easily from the medicine cabinet door? If yes, then simply have a glass company cut you a new one. If the medicine cabinet door is wood, chances are the back panel can be removed to access the mirror.

Rob Robillard is a general contractor, carpenter, editor of, and principal of a carpentry and renovation business. Send your questions to or tweet them to @robertrobillard. Subscribe to our free real estate newsletter at