Jim Rooney On The Level

Q. Our community has a periodic inspection of all our homes. It’s a covenant here. Recently we were advised that our roof was stained. Since many of the homes seem to have gotten the same advisory, the Homeowner’s Association has since informed us to ignore the advisory for this year. I seem to remember that you may have had a column concerning roof stains. I am interested in finding what the best solution may be if we are required to address this in the future.

I have talked with a reliable roofing company and they tell me they do not do roof cleaning. They recommend a zinc strip be installed to address this problem now and for the future. It is, however, very expensive. What's your opinion?

A. I’ve discussed these stains before but due to the greater than average amount of warm and wet weather we’ve had over the past few years, conditions have been right for dark roof stains to occur so it’s become the number question I get even after wet basements. Most want to know what it is and, like you, what, if anything, can be done about it without tearing the roof off or breaking the bank. In the overall scheme of things those zinc strips may not seem so pricey.

It is air-borne algae. The spores are always floating around in the air and if you looked at the surface of a roof shingle under a magnifying glass you’d see that it’s a rough surface with lots of tiny crevasses into which these tiny creatures land, lodge and flourish. Ambient temperatures and moisture permitting.

Moss seems to prefer shady, north facing or tree covered roof surfaces but algae doesn’t seem to care. Moss can be destructive and troublesome to roof surfaces and create water back-ups and blockages in valleys and at roof intersections. Algae merely makes the roof look dirty and shabby without hurting it in any other way. That’s what gotten into your Homeowner’s Association’s knickers and they apparently haven’t quite developed a strategy for it yet.

Some try to power-wash these stains away. The word powerwash and roof should never be in the same sentence. Too much nozzle pressure and you've blown your roof off in the worst case. At the bare minimum, high-pressure-- and by that I mean water nozzle pressure greater than what comes out of a household faucet-- will shorten shingle life. Roof shingles are more delicate than people think.

The common deck and siding wash recipe that I give out, consisting of one up liquid laundry bleach with one quarter cup of automatic dishwashing detergent in a gallon of warm to hot water, will work too. It’s cheap and easy but be careful doing anything up on a roof if working on a roof is something you don’t do for a living. One small slip and your whole world changes—it’s not worth the chance. If you try, use a garden sprayer and work from the bottom up. Be careful to be even. I’ve seen botched jobs and they look as bad as the original problem.

Some area businesses offer roof cleaning and anyone with a cedar shingle roof I’m sure has contemplated hiring one from time to time. Now homeowners with asphalt shingles think about shingle cleaning. For future stain prevention there are strategies to consider.

If the time for re-roofing is approaching you can specify a replacement roof shingle that is manufactured with copper and magnesium granules imbedded in the surface that will inhibit if not prevent the growths from getting started. Most roof shingle manufacturers offer them and the cost isn’t that much more than regular shingles. They are very popular in the Deep South where roof algae and moss growth is relentless.

If you've got problems now with a young to mid-age roof you can buy metal strips which you place up near the peak of your roof for the length of the house and as the rain washes over the strips the oxides of the metals travel down the roof inhibiting growth. One source they can be obtained from the Chicago Metallic Co., South Austin Ave., Chicago IL 60638 for about $3.00 per lineal foot (www.chicagometallic.com/product). They come in three foot strips. Measure the length of your house and multiply that by two for the amount you'll need. Call the supplier for a quote to include shipping and handling. They can be reached at 1-800-638-5192. I'll bet these strips will take a couple of years to clean the roof off if the staining has taken hold but will certainly work to prevent it if applied to a newer roof. The company also sells a cleaner called Shingle Shield Roof Cleaner that is essentially bleach based.

Or you can buy a special roof and deck cleaner from K&B Custom Building Products Inc., P.O. Box 1323, Albertville AL 25950. Their phone is 1-800-776-9830. So far as I can tell this too is a bleach based product. A franchise called American Roof-Brite has an authorized dealer in Edgewater through Exterior Concepts. I’d wait until the weather gets cooler because just walking on a hot asphalt shingle can damage it and the roof stain police promise they wont be back for a year-- so you’ve got time.