Will Pressure Washing Damage My Composition Roof?


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The straight answer is yes. If you asked if water will damage a composition roof the answer is also yes. If you asked if direct sunlight will damage a composition roof the answer would also be yes. All three of the above are going to create wear and tear on your roof but not to the extent that a person should feel concerned each time their roof is exposed to one of them. Having worked several years in the roofing trade I often heard you should never pressure wash a composition roof, now that I am in the pressure washing business I hear that sentiment expressed with increased frequency. The fact of the matter is that in most cases that is very true. I have been on many roofs where someone preceded me with a pressure washer and destroyed every section of the roof they had set out to clean via pressure washing. If a person is not familiar with roofing systems and experienced with the accessories and functions of a pressure washing machine KEEP THEM OFF OF YOUR ROOF.

Now on the other hand I have yet to hear someone who is experienced and well practiced in the pressure washing trade express that a composition roof should never be cleaned with a pressure washer (they all do express a need for caution). Someone who knows how to regulate the output pressure (psi*) of their machine can easily drop it down to a much safer working level. Knowing the different accessories available for pressure washing is another must. Some nozzles have an output spray which is many times more abrasive than others. Being familiar with using a pressure washer also allows a professional pressure cleaner to account for the angle at which the spray is directed at the roof as well as the resulting deflection spray. Instead of being a danger to your roof, when the above credentials are met, having your roof pressure cleaned becomes a valuable tool in ensuring the longevity of your investment.

Moss is Dangerous

The opening comment of this article affirmed that pressure washing does damage a composition roof. However when done correctly the advantages outweigh the risks of failing to take action against invasive moss growth on your roof. By all means Practical Pressure strongly suggests that you take every effort necessary to keep moss from ever growing on your roof so that pressure washing is never needed. However at times it is necessary given the circumstances. To Illustrate: Chemotherapy is not "good" for the human body but when cancer strikes it may be absolutely necessary for a person to be treated with it, and many people have enjoyed a satisfying and prolonged life as a result of accepting the treatment. Pressure washing a composition roof covered in moss is very much the same, though pressure washing is obviously going to produce a limited amount of wear and tear, in the long run it can, in large measure, actually increase the life of the roof. The effects of moss growth on your roof can be devastating even after a relatively short period of time. Moss often strips the protective granulated surface off of the shingles it grows on and can even go so far as to eat holes clear through the roofing. The sooner you have it removed the longer your roof will last. Even roofs which have been pressure washed multiple times by a professional pressure cleaner have proved to be in much much better condition than a roof that was left uncared for when moss began to appear.

It is true that there are other ways to remove moss from your roof but usually the alternative is not an improvement over pressure washing. Some common instruments I have observed or heard reported to have been used to remove moss are: screw drivers, flat bars, pry bars, putty knives and wire brushes. Certainly it could not be said that these instruments provide a less abrasive or less damaging method of removing moss from a composition roof. It is possible to kill the moss with out pressure washing by using things such as granulated and powdered moss killers but even then the moss will most often stubbornly cling to the roof and continue to hold moisture. Live or dead moss will retain water on your roof subjecting it to decay and it will also assist in collecting other debris to pile up on your roof.

So in consideration of the above factors Practical Pressure can, in good faith, state that your roof is being well served when it is properly pressure washed by an experienced professional.

Looking for a New Comp Roof? May We Please Recommend - Pritchett's Roofing


In view of the potential dangers in damaging your roof via pressure washing and the possible fall hazards we recommend that you do hire a professional to care for this maintenance should the need arise. Practical Pressure has experience not only in pressure washing but has also spent years in the professional roofing trade. We can assure you that with our experience in pressure washing as well as with roofs that your composition roof is in good hands with Practical Pressure.



What About Algae on my Roof?

How can I Prevent Moss and Algae from Growing on my Roof?

What About Lichen?


* PSI - pounds per square inch








See Picture of Shingles Damaged By Inexperience


See Shingles Damaged by Moss


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Practical Pressure

Professional Pressure Washing Services

"Keeping the Green State in a Clean State"

We provide professional exterior cleaning services for the Greater Puget Sound Region of Washington State. Practical Pressure is based in Tacoma, Washington and offers cleaning in the following cities and towns.

Seattle, Tacoma, Lakewood, Lacey, Olympia, Tumwater, Auburn, Kent, Black Diamond, Puyallup, Bellevue, Redmond, Renton, Tukwila, Federal Way, Milton, DuPont, Steilacoom, Spanaway and more.

Our services include roof cleaning (tile, shake and composition) maintenance and repairs as well as moss removal and moss prevention. We power wash decks, driveways, siding, gutters (we also do gutter cleaning), and just about anything else that you may want cleaned.

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