Ask Tom & Leslie

Ridding Your Roof of Alage Stains

My 6-year-old roof has some nasty black staining that I believe is a moss or algae. Can you suggest a product to get rid of this and prevent it from returning? Also, is this a do-it-yourself project?
Mark F.
Westfield, NJ

Sounds like your asphalt shingle roof has been marked by blue-green algae or "moss", a typical phenomenon in areas with hot, humid summers. Removing this is certainly a DIY project as long as you have the proper gear to reach the affected area safely (depending on your roof’s pitch and design, a ladder or scaffold, along with extra rigging, will be required). To remove, you can either purchase a ready-made cleaning/antifungal solution at your local hardware store or home center, or make your own using one part bleach, three parts water and some tri-sodium phosphate (TSP) for extra cleaning action.

Before you begin, make sure to wet down any plantings around your home’s foundation in order to protect them from damage caused by the cleaning solution (even if you plan to cover them with tarps while you’re working). Then head for the roof and use a plastic garden pump sprayer to apply the solution to affected areas, letting it sit just as long as is specified by package instructions or, if you’ve made your own mix, 15 minutes. Then rinse it away using a garden hose (do not use a pressure washer, which can damage your shingles). If some stains remain, allow the roof to dry completely before making another pass with your cleaning solution. Also repeat the rinsing of those landscape plantings once you’re done with the job.

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