Does cleaning algae and moss off an asphalt shingle roof prolong its life?

I have this on parts that are always in shadow. It's an asphalt shingle roof 9 years old rated 40 years. Generally in good condition.

Power washing could harm the roof. I can't do the work myself because it's a tall house with mostly steep roof lines way outside my comfort zone. I'd have to pay someone quite a lot to do it.

So the question is: Is it a good investment in the long term health of my roof to do it? Or is it the opposite, should I avoid having people walking, scrubbing, spraying, my shingles? Is it purely a matter of appearance? The appearance doesn't bother me.

  • 1
    put a strip of zinc on the roof above the mossy area ... rain will carry small amounts of zinc into the moss and kill it
    – jsotola
    Jun 15, 2021 at 21:37
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    You can extend the life of the roof with a little maintenance. I purchase 20 lb bags of zinc power it takes longer than copper sulfate but at 1/3 the price I have time. It’s cheaper in the bags compared to the very expensive cans of moss be gone. Absolutely it will save you in the long run in my neck of the woods a treatment every other or third year can double the roof life, well worth it but don’t scrub or power wash. As jsotola +states zinc can help keep it clear but it needs to be cleaned first.
    – Ed Beal
    Jun 15, 2021 at 22:22

2 Answers 2


There is no way in hell you power wash an asphalt shingled roof. You will ruin the shingles and possible squirt water under. Shingles are made to cover the roof from water at all angles, they are designed to cover the roof from water generally shooting down.

I had a roof that had a few trees over it. It too got moss, some algae. The best way to deal with the moss is to go up on the roof (summer is best) the day after it rains on a hot day. The moss will still have water it is retaining. Bring a small semi-stiff broom with you and literally nudge/pop the piece of moss out with the broom. They pop out generally really easy.

After you do that hit the roof with a leaf blower and get all of the debris off. Best to blower with the shingles not under them. You really want to get the loose dirt the moss has collect as you don't want anything lifting the shingles up.

For the algae there are numerous products that you just spray on - always good to do it about 1-2 days before a storm. These products require no washing after. I also would concentrate on just the problem areas not the whole roof.

On my old house this was just a yearly routine that I did every June. A small amount of moss will probably not hurt your roof but as it grows it gets big enough to pull up the shingles and wicks water under. Also I have had shingles deform and get brittle after detached (thinking about houses I flipped). I have had to repair/replace a few roofs in my life that probably could have made it another 5-10 years if maintained.

Summary: Nobody should be scrubbing or power washing your roof. A small broom and a leaf blower is all that I have ever used to clean off a roof and I don't use the broom to sweep, I used it to pop off anything stuck to the roof. An asphalt shingle roof that is getting moss means it is shaded or partially shaded. Maintaining it well without overdoing it means that thing could literally last forever. These shingles fail due to long sun exposure, too much wind/rain, and the wear layer coming off (wind, branches, cleaning...). The house I mentioned had 15 year rated asphalt shingles that were 40 years old with no leaks, cracking or tears... And only replaced them to sell the house.


I live in the land of moss and funguses (Oregon) we are in a drought and there is moss on my roof bright green. It rained last week it is raining this week and in all reality it will rain in the next 2 weeks it’s oregon.

I don’t treat it every year but every few years I have to on 1 side of the roof the other side the zinc strips have kept it clean.

I get on the roof after a rain and sprinkle copper sulfate , ok it got two expensive and I now use zinc I will put 3 rows down and a few weeks later go up and rinse or blow the dead moss and other fungus off I don’t want to rub the shingles or you find all the gravel that protects the shingles in your gutters.

If you allow the moss to grow it will get under the edges of the shingles and cause them to curl up then they hold water the moss gets further and soon it’s time for a new roof.

I have used a broom on houses I did not have weeks to wait and because of all the moss the bank report was the roof was in need of immediate repair, after a good cleaning and in some cases a bit of heat (probably not a diy trick) when the house was inspected the inspector estimated 10+ years on the roof, we picked up several houses in similar condition and all but 1 we were able to clean up and not have to put a new roof on.

Zinc strips help but it takes several not just 1 and on my current 1930 farm house a large oak creates enough shade and moss that we do have to treat it every few years.

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