It’s black and unsightly, and you’re probably thinking it’s mold, soot, or worse. The truth is, those ugly black spots on your roof are likely caused by gloeocapsa magma, a very persistent and common type of roof algae. This unwelcome guest invades roofs when they find what they need to feel at home — moisture — which is typically abundant due to shade and dew.
The first signs of this unattractive black staining on your roof almost always appear on the roof’s north sides because they receive less sunlight and are usually the areas where there is substantial tree cover. Algae can appear elsewhere first — but that’s the exception, not the rule.
Where Does This Algae Come From?
This type of roof-invading algae travels via the air, and it is quite aggressive. If your neighbor, for example, gets a few spores taking a foothold on their roof, then the entire neighborhood is subject to experiencing the same unsightly black algae growth eventually. Once it gains a foothold, it’s not likely to leave on its own. If you’ve got asphalt shingles, that’s doubly true since it simply adores the calcium carbonate they contain.
Over time, algae can affect the integrity of your roof. While algae bloom on your roof is mainly an aesthetic detractor, as time goes by, it can cause premature aging of your shingles due to the moisture it retains.
How Do I Get Rid of It?
A temporary solution to getting rid of algae from your roof is to spray it with a solution of one cup of trisodium phosphate, one gallon of bleach, and five gallons of water. Allow the solution to sit on the roof for around 20 minutes, then rinse it off. Be sure to protect any landscaping from the bleach and chemical runoff. A more permanent solution? Turn to the experts!