Composition roofs come in a variety of styles from relatively inexpensive 20 year 3 tab to very durable “presidential style” high profile 50 year products. According to Scott Harris of Shipshape Property, Oregon’s only board certified Master Inspector, composition roofs should be treated for moss every 3 years.
Moss treatment for your roof is a critical maintenance component. The rule of thumb is, if you can see moss on your roof from the ground, it’s time to treat it. If you let the moss grow, it will reduce the effective life of your roof, deform your shingles and cause them to be more prone to leak, and more prone to catching the wind and being blown off the roof, all of which will sooner or later require expensive repairs or replacement.
Once moss starts growing, it should be treated with an herbicide to kill the moss and retard its regrowth. There is no permanent cure, the moss will always grow back. There are some areas of your roof that almost never get sun, those may need treated every year, or perhaps every other year. All composite roofs should have preventative treatment every three years.
There is a difference between cleaning and treating roofs. Roof cleaning can be done by a company with general liability insurance. The cleaning is done by literally scraping and sweeping the moss off the roof. You should think carefully before allowing your roof to be pressure washed, since in addition to potential damage to composite roofing, pressure washing may void many manufacturers’ warranties.
Roof cleaning does remove most or all visible moss, but the roots (rhysomes) and spores that will be left behind will regenerate quickly, making cleaning only a not very cost effective option.
Roof treating, however, is regulated by the Oregon Department of Agriculture. The law requires that anyone who commercially treats roofs with any substance must be licensed by the ODA. There really aren’t any exceptions. And the product used must carry an EPA label that permits its use for killing moss.
What is important to you is that liability insurance to cover moss treatment is not easy to get, and it is expensive. What this means is that your general, non-ODA licensed company is not going to have a policy that covers any damage from the treatment process. And yes, there are things that can go wrong, including potential damage to your rain gutter system, damage to plants, animals, water resources and even children, if the moss killer is not applied properly. That being said, the moss killer is safe, provided appropriate precautions are taken. Knowing those precautions is part of the licensing process.
Timing is important for moss treatment. To get the best results, moss should be treated while it is growing, mostly in Fall through Spring, and for best results moss should be treated on a dry day, followed by at least one more dry day. So you are looking for two dry days in a row—sometimes a hard thing to do here in the Portland area! We have a special truck outfitted for treating moss, and we will often clean your roof and get it ready for treatment on one visit, and then return to treat it during an appropriate weather window.
You should almost always have your gutters cleaned at the same time you treat for moss, to make sure that none of the moss killer is left in your rain gutters. It can cause the gutters to rust and reduce the useful life of your gutters. Please see our package discounts information [lin]k.
There are several options for roof cleaning, ranging from pressure washing to blowing with an air blower, to sweeping. We discourage using a pressure washer on your composition roof. Your composition roof is essentially thick tar paper with sand and gravel imbedded in it to slow down the tar’s deterioration due to heat and ultraviolet rays from the sun. The natural process of wind and rain tends to wash away the sand and gravel over time, which is why your roof wears out. Pressure washing greatly accelerates that process. Sometimes it is the only solution, but you have to balance the wear on your roof against the cost of other methods.
If there are just leaves and needles on your roof, usually blowing or even sweeping is enough to keep it clean, and this is far easier on your roof.
However, if you have moss, just blowing off the roof isn’t enough.
Our usual process for cleaning a moss-infested roof is to brush off the large moss with a broom or brush, leaving the low-lying moss and rhysomes (roots) on the roof. Then we treat with an EPA labeled moss killer (herbicide). The moss will immediately start to die, and over the next few months will blow and wash away in the wind and rain, leaving your roof clean.
However, if you are getting your house ready for sale, or are concerned about the esthetic appearance immediately, instead of over the long run, then your choices for a clean roof are either pressure washing or hand removal of the moss. Hand removal means taking a tool, such as flat-bladed screwdriver, and literally scraping moss off the edge of every individual composition shingle. This is a labor intensive process, and is usually done after the moss is sprayed and dead. However, the result is that the roof looks clean immediately.
For a free estimate, or to schedule your moss treatment and roof cleaning, please call us at (503) 407-3346.
Cedar Shake Roofs. We do not do Cedar Shake roof treatments at this time. We can clean them by blowing and removing debris, but we don’t pressure wash or treat Cedar Shake roofs. We do know some good people in this area, and would be glad to provide a referral for you.