Algae: What it is, what it isn't & what you can do about it

6/15/2017

While driving down the road and looking at the houses you pass, have you ever noticed the black streaking that forms on a roof? Your first inclination is mold or fungus, but believe it or not, it’s algae. More specifically, gloeocapsa magma or blue-green algae. Algae forms when moisture is present for extended periods of time. As it develops, it forms a protective sheathing that is dark colored, which gives the organism protection from harmful UV sun rays.

According to the Asphalt Shingle Manufacturers Association (ARMA), there is no scientific evidence that algae is damaging to asphalt shingles.  However, the dark-colored algae growth covers the reflective granules impacting the effectiveness of solar reflective roofs.

How to Prevent Algae Growth

In general, algae spores spread in two ways – by wind or by animal, which is why it is not unusual to find neighborhoods where algae growth is visible on multiple roofs. Since stopping the spreading of algae is difficult to stop, here are some of the best preventative actions to alleviate conditions that promote algae growth:

• Allow more sunlight to hit your roof by trimming tree branches.
• Ensure your rooftop is clear of debris such as leaves, sticks, acorns, etc.
• Regularly clean your gutters out to allow for proper water drainage.

The use of algae resistant roofing shingles on your roof replacement or new home roof installation will help significantly decrease algae buildup. Algae resistant roofing shingles are manufactured with granules containing copper which hinders the growth of blue-green algae. CertainTeed offers a variety of shingle designs and colors that carry the StreakFighter© Algae Resistance label, which indicates that they are warranted against algae for up to 15 years. If algae staining becomes apparent on shingles covered by the algae-resistant warranty, CertainTeed and most manufacturers will give customers the option of either cleaning or replacing the contaminated shingles.

Going to Combat with Algae

Unfortunately, the discoloration caused by algae is difficult to completely remove from roofing shingles, though, it can be lightened. To ensure proper maintenance, cleaning and repair of your roofing system, we suggest you contact a credentialed roofing contractor as they have the expertise and experience needed to take proper action. 

A recommended way to clean your roof would be using a 50:50 combination of laundry grade liquid chlorine bleach and water. This method is only temporary and can cause slight discoloration of your roof. However, other cleaning chemicals and methods should not be used as they are not covered in the product warranty, unless approved by CertainTeed.