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Roof Moss Prevention Service in Portland Oregon

Moss starting to grow on needle strewn shingles. Photo by Bradly Lewis
It is more economical to prevent moss than to let it grow and then remove it. This needle-strewn roof in Portland, Oregon is nurturing new moss growth. Photo by Bradly Lewis, Portland Oregon USA
Steps Towards Roof Moss Prevention
- Encourage Air Flow - Keep your tree branches at least 10 feet away from your roof so that air flow is not restricted.
- No Branches Over Roof - Keep your tree branches from encroaching on your roofs vertical airspace (no branches over the roof). Overhanging branches will drop sap and other tree debris onto your roof and significantly slow water from evaporating from your roof.
- Minimize Shade - Prune, thin or remove trees that are within ten feet or your roof or shade your roof (sometimes people would rather have the shade than this form of moss prevention). This especially important if you have a concrete tile roof. If it is your neighbor's tree, it is polite to contact them first and let them know of the problem their tree is causing. If the tree is encroaching into your property, you have a right to prune it back to the property line. It's better if they take responsibility for it though. If you need a referral to a good arborist, please contact me. I keep tabs on arborists with good prices and service.
- Neighbor's Trees - Talk to a neighbor about their trees if they encroach into your property's airspace. Keeping their branches away from your roof will help prevent moss.
- Keep Roof Clean - Keep debris blown off the roof in moss prone areas so that the roof can dry out with the sun and wind. This is especially important in valleys, shaded areas of the roof and in the areas of the roof closest to the gutters. If you're nervous about going on the roof, give me a call. This is a service I provide also.
- Moss Preventative Applied - Have a moss preventative solution applied to your roof as often as it needs it. Please talk to me about this because while the pesticide manufacturers suggest yearly applications, I've found that many roofs can go 4 to 5 years or more between preventative moss applications. Preventing moss is a service I provide. A moss preventative application will prevent moss when most everything else fails.
- Reduce Moss Spores - If your upwind neighbors have moss on their roof, talk to them about moss treatment. If you have neighbors with moss on their roofs, the moss spores will travel via wind and birds to your roof. This makes it much more likely for your roof to grow moss sooner or speed up its rate of growth. While stopping moss on all your neighbors' roofs may not be possible, the more neighbors are actively preventing moss on their roof, the better for your roof moss prevention efforts.
How a Roof Moss Preventative WorksTo prevent moss growth on composite/ 3 tab/ fiberglass shingle roofs, I use and recommend zinc sulphate. It is non staining, residual and very effective. I spray the moss preventative onto the areas of your roof that need it, let it dry and then it is done. The spraying process usually takes from one to two hours for the average sized roof. It takes about half to 6 hours for the moss preventative spray to dry depending on sunlight and wind. The moss preventative spray stays on the roof until the rains eventually slowly wash it away (about one year). The increased zinc concentration on the roof makes it inhospitable for moss. It takes from one to four years before moss will get started after the moss preventative has washed off your roof. As long as enough zinc concentration is on the roof, moss cannot get started. Zinc on the roof also has the side effect of stopping and killing mildew. This helps prevent roof staining. Click on the link to the left "request a quote" to get a quote on moss prevention for you and or your neighbor's roof.

A darker roof with the temporarily salty look of the moss treatment. It will last until the first rain or a few heavy dews. Photo by Bradly Lewis, Portland Oregon USA
Dark colored roofs will have a salty appearance that goes away in a few days or during the first rain after it has been sprayed with zinc. This appearance is normal and temporary.
My Roof Moss Prevention and Roof Moss Treatment Pesticide LicenseI am licensed in Oregon by the Oregon Department of Agriculture Pesticides Division to kill and prevent moss on buildings with registered moss preventatives. My License number is AG-L1004124CPO which you can verify at Oregon Dept of Agriculture website (put "bradly lewis" in the "name" search field.)
!WARNING!Some businesses operate without the Federally required pesticide license and do not carry insurance to protect your property and/or the people living there. Some do not have the required training to apply pesticides either. If you are solicited by such a business then please do your part in notifying the Oregon Department of Agriculture Pesticides division at 503-986-4635.
In addition, if you have roof moss removed by pressure washing or other methods, if a roof moss preventative is not applied, the roof moss may return within 6 months to one year. This is the reason that I've made efforts to obtain and keep my roof moss preventative license active with the Department of Agriculture Pesticides Division.
What does not work as a roof moss preventative
- Bleach water is effective at killing moss growth on tile roofs, however it is not effective at preventing moss.
- Some people try zinc strips. I don't recommend them because of their lack of effectiveness, expense and appearance. Read more about zinc strips. For zinc strips to be effective, you would need on average about a six inch wide exposed area every three to four feet along your roof. This would be expensive and also it would be unsightly in my opinion.

Moss readily grows on roofs with zinc strips. Photo by Bradly Lewis, Portland Oregon USA
 Branches shade roof encouraging roof moss to grow.
 Trees drops leaves, twigs and sap throughout the year, making this apartment roof dirty and encouraging moss growth.
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