Whats that green stuff (algae) on my roof and how do I get it off?

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We’ve all seen it, either on our roofs or passing by a home that has either green or black streaks. Looks rather unsightly right? Well believe it or not it can develop on your roof in as little as 1-2 months. What can often be misinterpreted as dirt, mold and mildew when in fact it is actually algae! Often times it can be green in color but typically it is usually black streaks that fade right down your roof.

Why do shingles get algae?

So what is algae exactly? Algae is typically air born. They typically can be carried by the wind, your pets or even by your very own clothing! Since they are usually in the air, they can spread from roof top to roof top pretty quickly in your neighborhood. To save money, most manufacturers have switched to shingles containing asphalt. They are mostly made up of fillers such as fiberglass and crushed limestone. These types of fillers encourage the growth of algae.

Weather Is a Huge Factor

Hot, humid and moist conditions tend to create the best environments for algae growth on your roof. But with the use of cheap shingles, it can be a problem in nearly every state of the United States. Typically, roof streaks or algae usually form on the north side of the house. Why you might ask? Because that side of the roof usually stays in the shade the entire day which tends of build up moisture on that side of the house, this, harboring the potential for algae growth.

Is algae harmful?

Algae is not harmful to your health, plain and simple. But after a period of time, algae growth can damage the UV granules that cover the roof that may eventually cause it to come off.

How can you get rid of the algae and black streaks?

While cleaning your roof is an okay thing to do occasionally, it can usually void any roof warranties that you may have as well as any insurance polices as well.

Typically most formulas contain chlorine bleach and trisodium phosphate as well as water. Lye is much more effective then bleach but it is also much more corrosive as well and should be applied using full protective gear.

Install a Copper or Zinc Strip

Another way that you could help prevent algae from getting worse is by installing either a copper strip under the row of shingles closest to the peak of the roof. You could also install galvanized sheet metal as well, which does the same job and is also much cheaper as well. How will doing this help the cause? During a rainstorm, the water will first interact with either of these materials then run down the entire roof with algae killing molecules killing any potential growth.

While you cant permanently get rid of algae or even stop it from ever happening again, the best option in cleaning your roof is just to call the professionals to do it.

Craig McPeck