Washing January: How Do I Get Black Streaks on my Roof

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After a long winter many homes in our area have ugly streaks running down your asphalt shingled roof. Not only is it unsightly, it can also damage your roof. If you are experiencing this problem Elite’s team members can help you.

What causes Those Black Streaks?

If you live in a humid area you probably see those black streaks on homes pretty frequently. Those dark streaks look like dirt, or soot as they flow down your roof. But that’s not what’s causing the problem. It is actually a plant called blue-green algae.


Blue-green algae will start in small spots on your roof, but within a few months, they are already looking like streaks. You might expect algae to be a greenish color, however, the algae forms a protective coating from UV rays that cause it to appear black. Most of the time it forms on asphalt roofing but it can appear on other types of roofing as well.

How Does the Algae Get on My Roof?

Algae start from spores that spread by the wind, animals or birds, and even people. Once it gets a start on one rooftop it spreads to other homes in the community. You’ll notice it on many homes in the same neighborhood.


Algae became a problem when shingle manufacturers started adding limestone to asphalt shingles. Limestone is food for algae. That’s why the appearance of algae on roofs is a relatively new problem.

Does the Weather cause Algae Growth?

Algae likes a humid environment. If you live in an area like ours you are probably seeing algae appear. Algae has also started appearing on roofs in that experience very cold winters but still have humid summers.


Algae is not harmful by itself but can cause premature drying and aging of your roof. If a fungus joins the algae it can form a lichen. Lichen is a living plant that will send roots out, and that will damage your roof.

How Do I Get Rid of the Black Streaks?

You can clean algae off your roof with a solution of trisodium phosphate (TSP), bleach and water or using a commercial product. Before you get started to check with your roofing manufacturer to make sure it does not void your warranty.

Check the weather forecast and choose an overcast and calm day. If the sun is shining it will dry the solution that is applied to the shingles. If it is windy the wind will carry the solution where you don’t want it.

You’re going to need some safety equipment. Safety glasses, protective coating, rubber gloves, and slip resistant shoes are needed. You might also want to use a harness in case a fall happens.

Remove anything that could potentially get sprayed by the solution such lawn furniture on your deck or patio. There is a chance the solution used may kill landscaping, so be careful and thoroughly check out the product you use.

Put the cleaning solution in a pump style garden sprayer. Start at the top of your roof and use long strokes to apply the solution to a small area, about 4 feet square. Allow the solution to soak into the algae about 20 minutes. Do not walk on the sprayed area as the cleaning solution and algae can become very slippery!

How to Powerwash Your Roof to Get Rid of Streaks

Get in touch with our company in order to powerwash your roof if the cleaning solution doesn’t work. Our team will come out and take care of it for you. We recommend you only use a professional for this job to make sure you don’t destroy your roof. 

After the solution has soaked into the algae take a garden hose and hose off the solution and algae.

Call Us and We Can Help

If you would rather not get on your roof give the Elite Power Washing team a call. We can restore your roof and have it looking beautiful again.

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