Soft Washing in San Antonio, TX

Although these dark spots and ugly black streaks on your roof may look like dirt, mildew, soot or mold, what they really are is algae. The most common type is known as gloeocapsa magma — also known as blue green algae. This algae growth usually begins as small spots and then eventually becomes visible streaks. By the time this algae is noticed by the homeowner, it has usually been on the roof at least two or more months.

Why does these algae appear to be black? Gloeocapsa forms a protective darkly pigmented outer coating that shields the algae from damaging UV rays. This is what makes those unattractive black streaks on your roof! Although algae can be found on all types of roofing, it tends to be most common on asphalt shingles.

Algae spores are airborne. They can be carried by wind, animals and even on your clothing. Because these spores are airborne, they can quickly spread from rooftop to rooftop in a neighborhood. Why does roof algae seem to be more common today that it was 20 years ago? Traditionally, asphalt shingles got their name from being made up of mainly asphalt, an oil-based product, and felt material.

To save money, most shingle manufacturers have switched to shingles containing asphalt but mostly made up of fillers such as fiberglass and crushed limestone, which encourages the growth of algae. These algae use the crushed limestone filler as a main food source.

Weather is a factor in algae growth on shingles

Coastal, warm and humid climates tend to create the friendliest environments for algae growth, although the use of cheaper shingles has made algae growth a problem in almost every part of the United States. Even parts of the country that have cold winter seasons, such as the northeast or Midwest, still have problems with roof streaks caused by algae because they also experience hot and humid summers.

Often homes in algae prone areas will see roof algae on the north side of the house. Why? Because when the sun goes through the sky during the day, the northern part of your house’s roof is shaded for most of the day. This shade allows moisture to accumulate and provides the ideal environment for algae growth.

Gutters draining directly onto the roof and overhanging trees are also contributing factors for roof algae. A shady or damp surface also prevents the sun from drying the roof quickly, encouraging stuff to grow.

Is this roof algae harmful or dangerous?

Roof algae is not harmful or dangerous, but after some time, the algae can cause the protective UV granules that cover roofing shingles to begin to come off, eventually drying them out. Fungus, which also travels through the air, can combine with algae already present on your roof and form into lichen. This lichen feeds off both the algae and the shingle filler. Unlike algae, lichen can develop roots, which makes it harder to remove than algae alone.

Roof algae can be removed by a  roof cleaning.

The important thing to know is that while an occasional cleaning should not harm your roof, doing it yourself may void any roof warranties or homeowner insurance policies you may have.

An internet search on how to clean black streaks on your roof will turn up several different homemade formulas as well as commercial brands for getting rid of roof algae.

Cleaning the roof yourself

If you decide to clean the roof yourself, never, ever use a power washer, even on its lowest setting. Not only is using a power washer pretty much guaranteed to void any roof warranties, it can damage shingles by causing the protective coating, or even the shingles themselves, to come off.

Cleaning your roof will require some preparation. Remove any lawn furniture and cover vegetation and landscaping. Overspray is inevitable, and even if the product you use is not considered toxic, the runoff from your roof can cause plenty of mess on the ground as well.

Check the weather forecast and plan on doing your cleaning on a cool or overcast day with little or no wind to reduce the chance of the spray going other places besides your roof. A cloudy or overcast day prevents the cleaner from evaporating too quickly.

If you know who manufactured your roofing shingles, check their website for specific cleaning recommendations or products. When using a commercially available roof-cleaning product make sure to follow the manufacturer’s instructions exactly.
Be sure to wear eye protection, slip resistant shoes, protective clothing and rubber gloves. It's good to have a friend with you for safety’s sake and to easily give you any equipment you might need.
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It is best to start at the top of the roof and spray down since spraying water up at your shingles can loosen them. Each strip of shingles that you clean should only be about 4 foot wide. Do not stand on the wet part of the roof while you are cleaning, because it will be very slippery. You might want to wear a fall-protection harness.
After wetting down the roof with the solution, allow it to remain there for 15-20 minutes before rinsing. If you are on the roof at this time, it’s best not to walk around much since the combination of the roof algae and the solution can cause the shingles to be slick.
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Once the mixture has been absorbed, rinse off the solution using a regular garden house. Make sure you go slowly and use even strokes. If not, you may end up with random dirty patches because you skipped over parts of your roof too quickly.

If you don’t want to climb around on a slippery roof or your shingle manufacturer will void your warranty if you try to clean your roof yourself, you should contact a professional roof cleaning service to get rid of those ugly black algae stains on your roof.

Softwash Pros USA is your local roof cleaning experts. We are a local veteran and family-owned business and only use algae treatment products that are biodegradable and non-corrosive. We never power wash, but apply our eco-friendly treatment using a gentle “garden sprayer” that does not require any rinsing. We also do not walk around on your roof which protects your roof and our applicators. The result is a beautifully restored roof with no potential damage to people, pets, or property!