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Roof Shingles with Copper – Algae Resistant

Asphalt shingles are a very common building material in many new homes built in the Midwest. Even homes that cost a cool seven figures can sport premium cut shingles that look like slate or cedar shakes. But no matter how much you spend on your new home or its roof, the shingles can develop ugly black streaks in short order if you do not purchase special algae-resistant shingles.

The ugly stains I am talking about often look like upside down ice cream cones. Far up on north or east facing roofs you may see a small black spot and a widening fan of black that grows ands spreads as it heads towards the gutter line. There can be multiple areas of this streaking. In the worst cases, the entire roof turns a disgraceful color of deep gray or black.

The cause of this streaking is a simple organism - Gloeocapsa magma. This microscopic organism or algae actually eats an ingredient found in many asphalt shingles. The algae is harmless and the feeding does not cause any damage whatsoever to the shingles. The dark coloration is simply a buildup of the dead dark discolored cells that sluff off of the actively growing algae.

The algae organism has been around for years but it only recently became a problem because of a significant change in how asphalt shingles are made. Years ago a heavy felt paper was used as the foundation of the shingle. This thick felt mat absorbed the liquid asphalt that creates the waterproof barrier on your roof. The felt was made from cheap cotton rags. But the introduction of polyester fabrics 35 years ago caused the cotton rag market to shrink. Due to a dwindling supply of raw materials, the felt manufactures developed fiberglass mats and thus fiberglass shingles were born.

But the trouble with fiberglass is that it didn't absorb as much asphalt and the resulting shingle was simply too lightweight. Shingle manufacturers decided to add weight to the shingles by combining powdered limestone with the liquid asphalt. It worked. The resulting shingles were close to the original thickness and weight of those made with the traditional thick felt mats.

Everyone seemed to be happy for a few years but all of a sudden roofs in humid climates started to develop the black streaking. Upon investigation, it turns out that the powdered limestone was a scrumptious food for the algae! The algae had been on roofs for years, but it never was able to grow as there was nothing to eat.

It didn't take too long to figure out how to prevent the growth of algae on roofs. Those roofs that sported copper or zinc metal flashings at plumbing vent pipes, chimneys or ridges had no algae growth below those areas where the flashing was exposed to the weather. These metal flashings sacrifice small amounts of the actual metal due to weathering forces. Each time it rained, some of the copper or zinc washed down on to the roofs. This microscopic bits of metal poisoned the algae and it simply would not grow.

The good news is that you can buy new shingles that have copper built in to the colored granules. You can't see the copper, but it is there. It weathers just the same as a solid metal flashing and the entire roof surface becomes unpalatable to the algae. These special shingles cost a little bit extra, but they are well worth it if you want your roof to look like new for its entire life.

If your existing roof is stained with the algae and you need to clean it so you sell your house for more money, you can clean the roof. I have found that oxygen bleach is the safest way to do this job. Oxygen bleach is a powder that is mixed with water. You apply the solution to a cool roof and let it soak for 20 to 30 minutes. It is important to keep the roof surface wet with the solution. At the end of the wait period, lightly scrub with a push broom and rinse with a garden hose. Difficult stains may require multiple cleanings.

Once the existing roof is clean, you can keep it algae-free by installing strips of copper at key locations. You simply want rain water to be able to hit a 3 or 4 inch wide area of copper. Install the strips at the top roof ridge and any other place at the top of a roof so that you are fully protected. This copper can be readily purchased at a roofing supply wholesale business that sells tin, stick solder and other sheet metal supply to roofers. Simply look in the Yellow Pages under "Roofing - Supplies".


Message from Tim:

Years ago while researching a column about cleaning decks, I discovered the wonders of Oxygen Bleach. It is perhaps the 'greenest' cleaner I know of as it uses oxygen ions to break apart stains, dirt and odor molecules. There are no harsh chemicals, and it works on just about anything that is water washable.

I decided to create my own special blend using ingredients made in the USA. In fact, the raw materials in the active ingredient are food-grade quality registered with the FDA. I call my product Stain Solver. I urge you to use it to help with cleaning your roof shingles. You will be amazed at the results!

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