I get a LOT of questions from potential customers on roof cleaning or roof washing. Here are a few of the most commonly asked ones: What’s growing on our roof? Will the “stuff” on my roof damage it or does it just look ugly? What’s the best process or method to clean our roof? Will the roof cleaning get rid of all the black streaks, moss, and lichens? In other words, what can I expect my roof to look like when you’re done? I’m going to answer these questions from the perspective of an asphalt shingle roof since that is by far the most common roofing material in the northeast. However, most of the information below is applicable to various roof types and materials.

Living in the northeast, what’s growing on your roof is likely one of three things: Algae, moss, or lichens. We frequently find that all three will be present on the same roof. The most common algae that causes roof discoloration, such as the black streaking, is called Gloeocapsa Magma. You may have never heard of lichens so I’ve included a picture below of what lichens will look like on your roof. Bear in mind that lichens vary greatly in color and may be much more prevalent on your roof than you realize if their color is similar to your actual roof color.

Lichens Growing on an Asphalt Shingle Roof

Firstly, they definitely affect the aesthetics of your home. Secondly, they can damage your roof although not in the same way or to the same degree. For example, according to ARMA (Asphalt Roofing Manufacturers Association), there is no scientific evidence to suggest that the algae which causes the roof discoloration is damaging to the roof itself. However, the dark discoloration would certainly negatively impact a highly-reflective “cool” roof. For most home owners, the algae which causes the black/brown streaking and discoloration is generally only a cosmetic or aesthetic issue.

Lichens and moss can be much more detrimental to your roof as they will cause the roof to retain excessive moisture.  ARMA states: “Moss can be detrimental to asphalt shingle performance. Moss can cause the leading edges of the shingles to lift or curl, which increases the risk of shingle blow-off during wind events. In severe cases, moss build-up can cause lateral water movement resulting in moisture damage to the roof deck or may even cause leaks.” No one wants to replace their roof any sooner than needed and we certainly don’t want water damage to our home. Thus, if you notice that moss or lichens are growing on your roof, it is best to address it immediately rather than wait. Since the environment on your roof is conducive to the growth, the moss and lichens will only continue to spread if left untreated.

If you want to know how to clean your Ninja blender, do you take out your George Foreman grill owner’s manual? If you want to know what the warning light means on your 2016 Audi, do you grab the 1997 Honda Accord owner’s manual you’ve got from your first car when you were 16 years old? Of course not! Maybe it is silly or just obvious, but when we want to know how to maintain, fix, or clean something, we go to the person or company who made the product so they can tell us how to do it, right? I’ve referenced ARMA a couple times already. Why? ARMA stands for the Asphalt Roofing Manufacturers Association. You can find their Website at this URL:  http://www.asphaltroofing.org/  They are an association made up of companies that actually make asphalt shingles, companies such as Owens Corning, Atlas, and GAF. ARMA has issued technical bulletins on how to properly clean asphalt shingle roofs. I’ve included links to two of them at the end of this post. The bottom line is, the method outlined by ARMA is the method a professional roof cleaner should be using to clean your roof. Never assume that this is the case. Always ask, always! Below is a short video of an Epic View roof cleaning in progress.

When following the process as outlined by ARMA you will find that the black discoloration and streaking will be gone by the time the roof cleaning pro leaves your home. The lichens and moss are killed by the cleaning solution and will turn white followed by brown as they dry out. This means that the lichens and moss are dead. However, the lichens and moss will not be removed right away? Why not, you’re wondering. Because we want to remove them in the gentlest manner possible for your roof’s well-being. Removing them right away would require scraping them off, power washing them off, or some other ‘not-so-gentle’ method. Mother Nature is a gentle mother and the one best to care for getting all the dead moss and lichens off your roof. How long will she take to do that? Usually she takes 3 to 6 months, although it can be less, and in some cases more. Take courage! Your roof will continue to look better! Just a bit of patience is needed.

Well that’s it. Hopefully I was able to cover the basics with enough supporting detail without completely boring you to death!

As mentioned above, here I’ve included links to two of ARMA’s technical bulletins on cleaning roofs.