Roof algae, known scientifically as Gloeocapsa magma, is a widespread problem that many homeowners across the United States face. This organism has a tendency to make homes look ugly, and if left untreated, it can do some serious damage to roofs—algae can weaken roofing materials, and the stains they leave can lessen the appearance of a roof and even lead to decreased property values. Algae like to hang out in places that don't get much sun, and they tend to show up on roofs with dark shingles. Although they claim to not do much beyond appearance damage, what they really do is hang out and keep your roof moist, a condition that can lead to a lot of roofing problems. While roof algae might seem like an aesthetic issue, it can easily morph into a problem that's bad for the roof's health.
When it comes to roof algae, prevention is always better than cure. One of the most straightforward but effective preventative measures is to install zinc or copper strips along the roof's ridge. These roofs "rain metal," as the saying goes, and the ions released when it rains (or snows) create a very algae-unfriendly environment. The regular maintenance and cleaning of a roof can also go a long way in preventing its formation. Besides that, you can hardly be algae's friend if you allow tree branches to overhang your roof, since it is their second-best environment (after shady basements) to live in. At least trim back those branches, and if your attic isn't ventilated properly, ask a contractor to ventilate it. Otherwise, you're asking for just about any alga to live on your roof. Finally, algae-resistant shingles are a great idea whenever you have to replace your roof.
If algae have already taken hold, your roof is in danger. You need to move on this situation pronto. Of course, we are not going to start with harmful high-pressure washing, as that would only press the disease further into the shingle. Some gentle 'low pressure' (I paid an expert to use the right words here) cleaning is what indeed is best, followed up with a proper preventive regimen for the algae to not only not come back but also be physically impossible for any future algae to hold on. Should you find yourself in need of this kind of treatment, either do it yourself using a not-too-strong bleach solution (and following my thoroughly researched and reported advice on not harming yourself or your vegetation) or pay a professional who knows what they are doing and has the right gear, and who can get your roof back to Stage Zero without harming any shingles (you would have to take a course in shingle repair to know how to do it right).
