De Marne: Mossy roof doesn't need to be replaced
Question: The asphalt shingles on our house were replaced with fiberglass shingles (CertainTeed 40-year) in 1999. Moss is now growing on the roof to the point of causing concern, and roof replacement is under consideration.
Shade trees may contribute to a small area of moss, but the roof is generally exposed to the sun and is as dry as possible in the Pittsburgh area.
What is your opinion of algae-resistant fiberglass shingles? It seems that the algae resistance guarantee is short-term — 10 to 15 years.
What is your opinion of a metal roof? Would a metal roof eliminate the moss problem? (There would be no limestone, and some metals would be galvanized.) What metal and finish do you recommend? Do you have recommendations for installation techniques?
Thank you for any help that you can provide.
— Pennsylvania, via email
Answer: Moss on a shingle roof is not a reason for replacing the shingles, but the age of the shingles and their condition are. Your shingles are 17 years into the 40-year warranty listed for the type you have. But, in my experience, the great majority of shingles do not last as many years as the stated warranty, and collecting on warranties is an excruciating hassle, often leading to frustrating litigation.
You can have the moss removed by professional roof cleaners or do it yourself by spraying a solution of one of the several roof-cleaning chemicals on the market.
Here are some chemical preparations available online: Wet and Forget, which claims to be biodegradable; Spray and Forget; and Roof Wash.
I have used Wet and Forget successfully for a variety of cleaning jobs around the house. Follow the directions on the containers.
You can also make a solution of equal parts white vinegar and water and spray it on the affected areas. It will make the environment acidic and kill the moss over time.
Algae are not the same thing as moss, and the limited time warranty for algae-resistant shingles is far less than the expected life of the product.
Metal roofs are free of the vegetation growing on roof shingles. Screw-on-type metal panels would be competitive with shingles, but standing-seam roofs are more expensive. It does not seem to be the time to go to that expense, considering that the roof can be cleaned.
Send questions to Henri de Marne at First Aid for the Ailing House, Universal Uclick, 1130 Walnut St., Kansas City, MO 64106; or email firstname.lastname@example.org.