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Here's How: Roof Stains

James Dulley on

Dear James: My house has a light-colored roof and it needs to be replaced. It has always had a problem with dark stains on it. What is causing the stains and how do I avoid them on the new roof? -- Peggy K.

Dear Peggy: The staining problem is very common and unattractive, but it can be eliminated. Don't switch to dark shingles to hide the stains when you reroof your house. A dark roof will make your house much hotter during the summer and can cause excessive heat buildup in the roof itself. This high temperature is good for neither the shingles nor the supporting lumber.

It is generally algae that causes the dark stains on a light-colored roof. You probably have fiberglass shingles on the house now. They are durable and good-quality, but they do tend to support the growth of algae more than the older asphalt shingles which used a cotton or other natural fiber base. Limestone granules are often used in the fiberglass shingles and this creates a friendly environment for this particular specie of algae.

This is not to say that fiberglass shingles are bad. I have them on my own home and they function very well and have looked great and clean for many years. If you have a particularly bad problem with the algae stains, select new shingles which are algae-resistant and follow a few simple tips to control it.

The algae-resistant shingles have fine particles of copper and zinc in their composition. Copper ions, in particular, will impede the growth of algae. Many new swimming pool filter systems introduce low levels of copper ions into the water to stop algae growth, so it is safe. Many ancient cultures also used copper and silver containers to purify drinking water.

Most major roofing shingle manufacturers offer algae-resistant shingles. If you have trouble finding them at your home center or building supply outlets, contact the following companies for names of local sources: Atlas Roofing, www.atlasroofing.com, (800) 933-2721; Certainteed, www.certainteed.com, (800) 782-8777; GAF, www.gaf.com, (877) 423-7663; and Malarkey Roofing, malarkeyroofing.com, (800) 545-1191.

If you are not going to replace your roof for a while and you want to reduce the algae staining problem, first clean off the stained areas. A solution of 25 percent bleach with water or deck cleaner should remove and kill it. Don't use an excessive amount of the bleach solution because it is hard on the landscaping which it drips on near your house.

Place a strip of copper sheet metal over the peak of the roof. When it rains, the water will pick up copper ions and they will flow over the algae. It is commonly available in seven-inch-wide strips. Nail it to the roof and use a little roofing cement or sealer under each nail head before you hammer it in. Stretching a few bare copper wires across the shingles will also give off more ions.

Your roof is probably well shaded or you would not have had the staining problem initially. Algae does not thrive well in a dry sunny location. Cut back some of the tree branches if possible to reduce the roof shading. This will also reduce the amount of fine organic debris which settles on the shingles from the trees.

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Send your questions to Here's How, 6906 Royalgreen Dr., Cincinnati, OH 45244 or visit www.dulley.com. To find out more about James Dulley and read features by other Creators Syndicate writers and cartoonists, visit the Creators Syndicate website at www.creators.com.

Copyright 2017 Creators Syndicate Inc.

 

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