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Roof Moss Treatments

About Roof Moss Treatments

This is a table giving you more information about the different ways of treating moss on asphalt/composition/comp/3-tab shingles (not tile or cedar-shake roofs). Composition roofs have granules on the surface that are made of a ceramic. They protect the water-resistant properties of the tar and asphalt in the shingles. When the granules are gone, it allows the tar to be exposed to the UV light and cause it to "spider" or crack. This also causes it to become more brittle and break off (in wind) etc. Granules on shingles are like paint is to your car. The granules need taken care of so that the shingles lifetime is maximized.

Table of Different Roof Moss Treatments

Zinc sulphate Kills moss completely. One trip. Makes moss shrivel up and darken in color (less noticeable). Leaves residue on roof (lasts about a year) that prevents future moss growth. So effective that I guarantee it will kill the moss and no regrowth for at least one year.
Laundry Detergent Kills moss quickly. Makes moss turn yellow and light green. It may dry out the roof and lead to granule loss if not washed off soon after application. This destroys the roof you are trying to protect. Only solution if you want to use this is to keep the detergent wet for 15 minutes and then wash it off the roof thoroughly. Bleach water solution is better alternative. It may help reduce or remove some roof stains by algae or mildew.
Zinc Strips Not very effective. Requires 4 inch exposure every 2 feet down your roof to prevent moss. Will not kill existing moss. Installation is time-consuming. Installation requires nails hammered into your roof. It weathers poorly, some strips break and flap around in wind. Cupping and curling cause uneven water distribution and appears to streak the roof. Very expensive to apply all required zinc strips to prevent moss. For all these reasons, I do not install zinc strips.
Bleach Water Solution A milder solution of bleach water can be sprayed on the roof to kill moss. This turns the moss lighter in color (yellow and lighter green) and helps remove some staining caused by mildew and algae. Do not treat your roof with using too strong of bleach solution. This will cause granule loss when the asphalt in the shingles lose their grip on the granules. A bleach solution will kill the moss quickly, but will not prevent future moss growth.
Mechanical brushing This causes granule loss unless the moss is killed first. Otherwise the moss' rhizomes (like roots) cling to the granules and the granules come off with the moss. Brushing off live moss causes the rhizomes to spread and causes the moss to spread. Only temporarily effective. This method is effective for treating small areas of very heavy moss growth prior to treating the moss. Alos effective after the moss has been killed. Labor-intensive process on live moss.
Pressure-washing Causes more granule loss than zinc-sulphate. Commonly known among contractors to remove 5-10 years from life of roof from granule loss. Commonly known to cause water damage and leaks around skylights. Removes moss quickly. Very messy when gutters overflow onto house siding and landscaping. Health issues with moss and mildew spores being blown into air. Moss pressure-washed off the roof may land in landscape and begin growing there. Not an option for older shingles that have fewer granules already. Better (if ever used) on newer roofs that will not show granule loss as much.Offers no moss prevention. Shingles may be torn off by pressure-washing hose. Water, mildew and moss particles can get blown between the shingles.


This page was last updated on 2009-01-21

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