Q&A / 

Black-Streaked Shingles – Roof Algae

Are you suffering from the stained roof syndrome? It's that dark staining that looks like someone spilled coffee up on your roof. This problem used to be associated with mildew in years past. Mildew is a by-product of fungi. However, it has been determined that another organism has invaded millions of newer asphalt shingle roofs around the USA. This organism is an algae, Gloeocapsa magma. It has experienced an explosive growth curve during the past 15 to 20 years quite by accident.


A large number of homeowners who are experiencing these roof stain problems are doing so for the first time. Even though they live in areas where the climate has not changed, the problem appears out of the blue.

In years past, the algae simply didn't have a food source. This changed with the introduction of fiberglass shingles during the past 20 years. The fiberglass shingles made today contain massive amounts of food that the algae loves to eat -- that food being limestone.

How in the world does limestone get into fiberglass shingles you might ask? It's simple. The limestone is added to the asphalt mixture as a filler or thickener. This rock has been added for decades.

Years ago an organic felt mat was used as the base for the shingles. This mat was saturated with asphalt and then coated with granules. Because of the absorptive qualities of the mat, it was able to soak up enough asphalt to give the finished shingle sufficient weight. The materials used for the mat were derived from the cotton rag scrap market.

Well, about 20 years ago, this rag market dried up because of the widespread introduction of synthetic textiles, such as nylon and polyester. The shingle manufacturers scrambled and decided to use fiberglass as a mat.

However, a problem quickly arose. The thinner fiberglass mat didn't absorb asphalt like the old organic mat. Something had to be added to the asphalt to increase the weight of the shingle. BINGO! My guess is, based on the explosion of black stains on roofs all across the USA, some manufacturers decided to use more limestone which is plentiful and cheap. Well, you know the rest of the story.

Flashings Solve the Problem

As people complained to the shingle manufacturers about this problem, they began to notice that on certain portions of some roofs the algae wouldn't grow. Commonly, these areas were just downslope of a chimney or a plumbing vent stack. It didn't take too long for them to figure out that just above these areas were zinc or copper metal roof flashings.

Apparently, each time it rains, small amounts of copper and zinc wash down the roof in theses areas. The minute amounts of these metals seem to be enough to poison the algae.

Well, the shingle manufacturers called up the Industrial Mineral Products Division of the 3M Corporation. You see, these are the guys that supply the shingle manufacturers with all those nice colored granules.

The 3M people figured out a way to coat certain granules with copper. These granules are then covered with the same color as the rest of the granules. Anyway, the copper actually leaks through the coloring and makes the shingle unsavory for the algae.

These shingles carry a lifetime warranty from many of the shingle manufacturers, so that you don't have to worry as to how long the copper will last.

Newer, Existing Roofs

Millions of people have roofs that are stained. But, they are not yet ready to replace all their shingles. So what should they (you) do? It's easy! You just need to clean your roof and introduce some copper as high as possible on your roof.

Cleaning a shingle roof that has this algae infestation is not that hard. It is DANGEROUS work, but not hard. The trick is to apply standard treated wood deck cleaners to your roof and follow the instructions.

However, you shouldn't use just any deck cleaner. You must use a deck cleaning product that contains a safe cleaning agent such as oxygen bleach. Sodium percarbonate does the same job as chlorine bleach. However, chlorine bleach is harmful to you, your roof, your gutters and downspouts, and any plants it might come in contact with. Want more information as to how to get oxygen bleach? Just click the link!

If you decide to clean your own roof, BE CAREFUL. Wet roofs are slippery. These deck cleaners are slippery. You can easily fall off your roof and either die or become permanently crippled. I'm serious. So, if you still want to do this, and not hire a professional, be sure to wear an OSHA-approved safety harness. Also, do not direct the hose spray UP the roof! Water can get under shingles and leak into your house. Always spray down the roof.

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 clean algae off your roof. You will be amazed at the results!

Column B82


Leave a Reply

You have to agree to the comment policy.