According to ARMA (Asphalt Roofing Manufacturers Association) and CASMA (Canadian Asphalt Shingle Manufacturers Association), pressure washing of shingle roofs are not recommended. Why is this you ask? Well pressure, even so called low pressure, can dislodge the little granules on the surface of the shingle exposing the underlying membrane to UV rays. This can cause premature failure of the shingle. It can also be cause for voiding your warranty.
These granules are vital to the health of your shingle. It not only provides the coloring of the shingle but prevents the underlying membrane from damage by the elements. Imaging what a flock of birds would do to your unprotected roof!
There are several roof cleaning chemicals being marketed today and most of them require medium pressure to be effective. What this means is that instead of a 3000 PSI pressure washer with one nozzle they want you to use a device with 3 nozzles that reduce the individual pressure at each nozzle down to some where in the range of 800 to 1300 psi. WOW that is still a lot of pressure. Think about it, at one point or another most of us have cleaned our own gutters and have noticed the little granules in the gutter from the shingles. Now these were removed by RAIN. Just think how many can be removed with a pressure washer even at 800 psi. Heck your garden has less than 100 psi and us usually around 60 or 70 psi and it can remove granules. Try it one day on a scrap piece of shingle and see if you remove granules. Do NOT try this on your roof.
The next time someone tries to sell you one of these products just say no thanks. The best and safest way to clean your roof is with a chemical solution recommended by ARMA that will kill the algae on your roof without the need for any pressure. Just spray on the mixture and then you have 2 options, leave it on for it's systemic value and wait for the rain to do the washing or you can completely rinse the roof with a garden hose. Stay tuned for the next post where I discuss the proper method of cleaning your roof.
Keep in mind that even though these chemicals can be dangerous irritants when handled incorrectly, when handled by a professional the risk are much much lower. Let a professional handle the cleaning as they have the proper knowledge, tanks, chemicals, pumps and insurance. This will be the cheapest option in the long run for the home owner.
Visit our Roof Cleaning Clarksville and Nashville web site for more information and videos.