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Question DetailsAsked on 5/2/2012

What is the best method for removing and treating moss on composition roof?

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5 Answers


This is really a 4 step process.

1) A manual cleaning to try to broom sweep as much debris from the roof, including moss and vegative debris composting between the channels in the shake/shingle.

2) A very light power wash performed only by a professional. It's very ez to destroy your roof and cause leaks if not properly trained on the use of a power washer. The pressure must be adjusted properly.

The use of chemicals, such as a bio-cide bleach can be attached to better power washers so that you are killing the moss, lichen and algae that remains after the power wash. However take warning, if using any of these chemicals it is IMPERATIVE that the bushes, plants, lawn, garden etc... be heavily saturated with water to prevent the killing of your lawn and gardens. Where the down spots drain, if the drain to grade should also be heavily flooded to dilute the checmicals that run off the roof while washing.

3) A preservative such as Total Wood Protectant (TWP) can then be applied. This preservative is optional but highly recommended to revitalize the lost natural resins in the wood. You'd treat your deck or fence. Why not your roof? Please keep in mind that water or acrylic based coatings are primarily useless, and the use of a deck or fence grade coating or preservative on your roof is also almost useless as the roof take much more beating and is much more important than a deck or fence. Only use quality oil based products for preserving your roof or don't waste your money.

4) Prevention of future vegative growth is also optional but recommended if you don't want to repeat the washing every few years. You really should consider a 5 year maintenance cycle of washing and preserving though. I recommend heavy metal strips such as zinc or copper be installed on the roof to help reduce the vegatitive growth from occuring. Plants don't like heavy metals and as the rain water rushes over the exposed strips, it takes micrscopic particals and washes those particles over your cedar roof.

If you plan to do this your self, be very careful as a wet cedar roof is slipperier than a slip-n-slide. Proper fall protection is a must as it's super ez to slip and fall.


Answered 8 years ago by ReliableAmericanRoof


Apparently the last person who answered doesn't know enough about roofing to know what a composition shingle is. They aren't cedar shakes. Anyway, a 50/50 bleach & water solution can work but can be hazardous to other vegetation below the roof. I've used it many times for patches of growth on roofs. Many roofing suppliers sell a chemical that kills the algae and moss. Some home improvement stores do as well. Be careful about sweeping your roof as you can pull the gravel from the shingles and ruin your roof. If the problem has been left unmaintained for some time you will only be able to clean so much from the roof. Also, be careful because it can get slick once you get it wet.

Todd Shell
Todd's Home Services

Answered 8 years ago by Todd's Home Services


Woops. It was late at night when I answered. Thanks for being so CRUDE with your response, Todd! Keep up the awesome work buddy!

I obviously only half read the question. Since around here nobody consideres washing an asphalt shingle roof, I assumed it was cedar without really reading. However much of what I said absolutely still applies. A bleach water mixture will kill just about anything, and heavy metal treatment will help prevent it from growing back.

On the flip side, you must be aware that a power washer has the potential of causing the illusion of black streaks, which is actually a result of removing too much granual. This means damage has been caused to the roof exposing the asphalt matt, which the granual is there to protect.

My suggestion is to make sure when it comes time to replace the roof, use a shingle with an algae relief type treatment such as CertainTeed Landmark which have copper granuals mixed with the ceramic granuals. Also make sure all your trees are cut back from the roof as well, make sure to manually remove any leaves, branches, seeds etc... when cleaning the gutters routinely twice annually.

Answered 8 years ago by ReliableAmericanRoof


"Reliable," crude I wasn't but looking at your other roofing answers I can say you do seem to know what you are talking about. The one answer here just doesn't match the the other knowledgeable answers you've given so based on the one someone may be led to believe the wrong thing about you. I'm glad you responded to clarify the reasoning for the answer so others don't discount you. We all make mistakes and I'm glad to see it was just caused by misreading and not intentionally giving bad advice.

Answered 8 years ago by Todd's Home Services


Have seen a chemical sold at local CostCo that kills algae on roof with very little effect on vegatation,, Copper strips with exposure of 4" are used by some Southern contractors algae proofing roofs. They suggest every 10 feet.


Answered 8 years ago by jccasper

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