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Roof Moss Prevention Service in Portland Oregon

Composition roof with pine needles and moss
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

  1. Encourage Air Flow - Keep your tree branches at least 10 feet away from your roof so that air flow is not restricted.
  2. 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.
  3. 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.
  4. 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.
  5. 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.
  6. 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.
  7. 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 Works

To 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 this link to request a quote/contact me to get a quote on moss prevention for you and or your neighbor's roof.
Dried roof moss treatment with temporary chalky look
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 2006 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.

How Long Does the Moss Prevention Last?

Great question. The photo above was taken after I treated this roof in 2006. After doing a neighbors house four years later, I asked these customers if I could look at the roof that was treated. They said "ok" and so I took some pictures so you could see results on their roof. On a typical 3-tab roof with no trees around and no close neighbors with moss, the treatments last over six years. I've done many houses like this and they are still in fine shape with no sign of moss. On this house, there was moss starting. I didn't brush any moss off. It weathered off the roof, even on the North side. I have a page with photos on it. The link is at the end of this paragraph. On the other hand, if you have a flatter pitch roof, with laminate shingles, under pine trees and you don't blow it off every year and avoid cleaning gutters (oofta), then you can expect from 1 to 4 years depending on rainfall and cloud cover for the years. Each roof I do comes with a minimum one year guarantee to kill the moss and no regrowth during that year. I have a very specific technique for applying the zinc that makes it last so long. Untrained applicators often yield poor results that require annual treatments. I repeat, my treatment lasts a long time. The application technique that I learned (partially by accident) works very well and saves customers repeated applications and maximizes the use of the same amount of pesticide used in a poorly applied treatment. See moss prevention duration photos of a roof treated four years earlier.

My Roof Moss Prevention and Roof Moss Treatment Pesticide License

I 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.)
I would like to highly recommend Bradly Lewis for the excellent work that he has done in the removal of moss and algae on our roof and in its preventative maintenance. Brad showed up on time, offered reliable advice, and did exactly what he stated. Brad was very professional in his interactions. I told my next door neighbor about his services. Mike B, Vancouver, WA."


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

  1. Bleach water is effective at killing moss growth on tile roofs, however it is not effective at preventing moss.
  2. 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 growing on composition roof that has zinc strips installed
    Moss readily grows on roofs with zinc strips. Photo by Bradly Lewis, Portland Oregon USA

    Roof moss growing in shade
    Branches shade roof encouraging roof moss to grow.

    Tree shading apartment roof causing moss to grow
    Trees drops leaves, twigs and sap throughout the year, making this apartment roof dirty and encouraging moss growth.

This page was last updated on 2011-04-09

Bradly Lewis Home Maintenance INC 503-481-8872
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