Unlike roof moss which is easily identified, those ugly black streaks and stains on your shingles though appear to be some sort of roof mold, a more accurate description would be to call it roof algae. This is a hardy species of algae called Gloeocapsa Magma, and if you aren’t using the right chemicals or methods it can be extremely difficult to remove. Call it roof mold, roof algae, roof mildew, or whatever else you want, but just be sure to clean it off in a timely and safe manner.
Just to be thorough, there are other types of organic growth that can form on a roof other than roof algae (or mold). There’s also the possibility of lichen or moss growth. Lichen is usually a whitish color, but it can also have tones of green, yellow, and brown. It often forms in patches of individual circles, each averaging about the size of a dime. It’s also noticeably raised from the surface, unlike the black algae stains.
Roof moss, on the other hand, almost always has a green color and if left untreated for several years will become so thick as to be noticeable from the ground. I’ve seen some situations where it’s been ignored for so long that it literally looks like a roof is covered with green carpet. Honestly I don’t know what people are thinking when they allow this to happen to their home especially when you can remove roof moss fairly easily most of the time.
So how does one go about treating a roof with lichen and/or moss? Well, in most cases it should be handled in the same manner as the black algae roof stains (or “roof mold“), which has already been described in length on this site. In a nutshell, a bleach or chlorine-based solution applied with non-pressure methods will kill lichen and moderate moss growth almost instantly. It should turn a whitish color within minutes, which tells you that it’s dead. Unlike black algae stains which come off immediately with the rinse phase of the cleaning, dead lichen and moss will require a few heavy rains to finish rinsing off the roof. It could take awhile but rest assured that lichen and most moss situations, once dead, will eventually dislodge and rinse off the roof thanks to mother nature.
If you are the impatient type and want the lichen and moss removed immediately, you’ll have to use a pressure washer, but as you should know by now I highly discourage the use of high pressure on a roof. In those rare cases where the moss is extremely thick and out of control (this is more common in the northwest) your only choice might be to use a pressure washer, but even in these extreme scenarios you should dial down the pressure and use extreme caution.
In summation, black roof “mold” stains (algae) should come off immediately if using the proper methods. Roof mold removal doesn’t have to be rocket science, people. White or green lichen and roof moss removal on the other hand, can be achieved by the same chemical solution but will need a few heavy rains to finish rinsing away. If this all just sounds like too much of a hassle and you’d rather keep your feet safely on the ground (good idea) then do take a look at our directory of non-pressure roof cleaning services. There’s more than likely a company in your area that knows how to remove your roof algae in a professional and safe manner.
The other reason you shouldn’t be scrubbing or pressure washing your roof stains is that in most cases it’s simply not necessary. I go into this in a lot more detail throughout this site, but the bottom line is that if your contractor is using the correct chemicals then no surface agitation should be required. You simply spray on the chemical with the help of a non-pressure pump, allow several minutes for it to kill the algae, and then rinse gently with a garden hose. The only rare instance where a power washer might be useful is with very thick, green moss, but if all you have are black algae roof stains then you should have no need for scrubbing or power washing. Make the mistake of cleaning your roof with high-pressure or aggressive agitation and you will probably only shorten its lifespan. Use the right roof stain remover without pressure and you will extend your roof’s lifespan.
on every job. Theoretically, a roof cleaning could be done with one person, but the ideal scenario would be to have two roof cleaners on site for your job, one to apply the chemical and do the rinsing at the roof level, and the other to remain on the ground for perimeter rinsing and just as a “safety valve” in case the roof-man needs assistance.
However, it’s important to understand that even though the sun helps to slow the growth of algae on southern-facing surfaces, it does not stop it. If you have stains beginning to develop on the northern-facing surfaces of your roof, it means that it’s just a matter of time before the entire roof is covered with algae stains. You might not yet see black stains on the southern-facing surfaces, but that doesn’t mean that algae hasn’t already taken root and begun to multiply in these areas.
store will work fine. Again this will help in keeping chem off your skin.