Removing Black Algae and Roof Moss

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While your roof may look great and be uniform in color while new, over time that can start to change. Eventually you might start to notice black patches on your roof and even directional lines where water seems to run off your roof and sometimes moss will be present. The black you are seeing is Gloeocapsa Magma, which is known as black algae or roof mold and is spread by airborne spores. Typically the presence of black algae occurs only on the north side of your home as that is the area least exposed to sunlight. This problem is also more prevalent in humid parts of the country and can affect entire neighborhoods as algae spread by air between homes, feeding on limestone filler in rooftops.



To remove this unsightly roof staining, you have a couple of options. One of those options is diluted bleach. With a mixture of 50% water and 50% bleach, spray your roof and let this mixture sit for a few minutes before rinsing. You will know when the algae and moss begin to die as the blackness on your roof will begin to whiten. Once you see this occurring, rinse the roof thoroughly but do not use a pressure washer as that can harm shingles. Do note that using bleach will get the job done but it some cases it can be damaging to shingles, causing them to become brittle and stiff. Also be careful using bleach if you have plants around the edges of your roof-spraying them down with water both before and after applying bleach to your roof will aid in keeping your plants safe throughout the bleaching process.



Safer than bleach is a product known as oxygen bleach, which comes in a powdered form such as OxiClean. Per the instructions on the package, mix oxygen bleach with water and the proper dilution, then spray onto your roof. Follow up with a scrub brush to further remove stains. In some cases when the algae discoloration is especially bad, a second application may be necessary, but this product is worth the extra work due to being safe for plants and gentle on shingles. Once the oxygen bleach has done its job, rinse the roof clean.



Moss and lichens can take extra time to dislodge and rinse away, even after being killed by cleaning products. Mother Nature has a way of taking care of this on her own with rain, but if she is being uncooperative, hosing your roof off a few days after the initial cleaning will help. If you have been plagued by roof algae in the past and do not wish to endure it again, when it comes time to replace your roof, do so with algae resistant shingles which will be marked with an AR. These shingles have the addition of zinc or copper which deter the growth of algae. Alternatively, applying strips of zinc or copper beneath shingles will accomplish the same thing.

For both the sake of appearance and the health of your roof, tackling roof algae, mold, and moss are necessary jobs. If you are not comfortable with roof work, professional services are available to do so for you and can be found in your local yellow pages. Should you decide to go ahead and attempt roof cleaning, do so with assistance and take great care to avoid falling, especially on roofs with an extreme pitch. In the case of roof algae, cleanliness, while important, should take a backseat to safety at all times.

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