Professional Roof Cleaners Association

Asphalt Roof Cleaning

AsphaltRoof PRCA

What is Asphalt Roof Cleaning?

Asphalt roof cleaning is the removal of organisms, such as algae, lichen, and moss from asphalt shingles.  While many surfaces can be easily cleaned with a good rain shower, most roofing materials require a more in depth cleaning process to remove these organisms and prevent the growth of large colonies.  Algae, lichen, and moss growth on asphalt shingles is most common in the Southern region of the United States, but can be found throughout the U.S. and Canada.  They thrive in moisture rich areas, but have been known to withstand antarctic conditions and droughts.

Does my roof have organic growth?  Where did it come from?

Have you noticed black stains on your asphalt roof?  These stains are usually heavier toward the bottom and taper up as they near the roof ridge.  These black stains are evidence of algae.  The reason the roof appears dirty with black streaks is because the algae has a protective cover, giving it a black color and protection from UV rays.

Algae and other growths spread from one infected roof to another. The spores will land on any surface as it is blown by winds or carried by animals. Once the algae spores make it to the roof, they will begin to accumulate.  The algae growth starts slowly and accelerates during rainy seasons.  Typically, algae first appears on the northern and most shady sections of your roof, which is why you may have only recently noticed its appearance.  Once the algae starts, lichen and moss will soon follow, opening up the possibility for roof damage.  These three support each other within the environment and will usually be found co-existing on most roofs.  Most of the time, homeowners are unaware that the lichen and moss are present until the roof has been cleaned, where the lichen and moss will turn white from the roof cleaning application. They usually blend in very well and are not visible from the ground. Take a look around your property.  If you can see moss and lichen growing on tree trunks, it may be a good precursor to your roof’s condition.

Why should an asphalt roof be cleaned?

Asphalt roof cleaning is a sound choice in extending the lifespan of your roof. The build-up of algae, lichen and moss will damage your asphalt shingles, resulting in an early roof replacement.  The Asphalt Roof Manufactures Association (ARMA) highly recommends regular cleaning and maintenance of your roof. The choice to maintain your roof’s surface should be an important and informed decision. If left untreated, the shingles will accumulate more organic growth and retain excessive moisture, causing deterioration and decomposition.  The valleys of your roof are especially vulnerable to deterioration due to the channeling of rain water, creating a breeding ground for the organisms.  Essentially, a roof that retains moisture is a roof that will eventually fail.

How should my asphalt roof be cleaned?

PRCA supports and recommends the same cleaning process that is suggested by the Asphalt Roof Manufacturers Association (ARMA), the National Roofing Contractors Association (NRCA), and all shingle manufacturers. These authoritative associations have studied and researched proper asphalt cleaning procedures.  They clearly state that a roof cleaner should not power wash a shingle roof with any kind of equipment attached to a power washer. PRCA members use the recommended non-pressure washing procedures and chemicals that the shingle manufacturers recommend.  Make sure that the contractor you choose uses the non-pressure process.  Ask them the most important question: Will you use a pressure washer on my roof? Pay close attention to their answer, specifically low-pressure answers.  Even the lowest setting on a pressure washer will cause damage to the shingles.  It will not extend the life of your roof and could void your existing warranty.

Who are ARMA and NRCA?

The Asphalt Roof Manufacturers Association (ARMA) is the professional collaboration of major roof manufacturers like GAF, IKO, Certainteed, Tamko, Pabco, and Owens Corning.  It also includes the suppliers of raw materials, like 3M, who make the granules used within the asphalt shingle production.  More information on ARMA can be found at asphaltroofing.org

The National Roofing Contractors Association (NRCA) is a professional association that is seen as the leading authority in the roofing industry.  They are the voice for various roofing contractors throughout the United States, and works with manufacturers to improve the industry as a whole.  More information on NRCA can be found at nrca.net.