Mold on roof

Old 12-06-03, 12:43 PM
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Mold on roof

We live in TN, where the summers are hot & humid. We've noticed a couple areas on the roof we have some mold on the shingles. The areas are shaded, so it probably makes the conditions right for mold.

The questions:
1. Does it hurt the roof?
2. Assuming it does (or at least assuming it does the roof no good), what's the best way to clean/kill it?

Old 12-06-03, 01:25 PM
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Not mold, but probably algae and/or moss.
There are roof cleaning products on the market, but a 10% solution of household bleach along with a bit of liquid soap should help remedy the problem. It should be sprayed/mopped on then hosed off after about 10 minutes. A light pressure washing between 500 and 700 psi will help remove the dead material. Do not use a higher pressure, as it could remove the stone granules from the shingles. Start from the gutter and work your way up to the peak to avoid streaks.

Old 12-06-03, 04:45 PM
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This needs to be a "sticky"..............

Anyway, the mold (I agree, it is most likely algae or fungus) does not "hurt" your roof. It is just unsightly and it will spread very fast.

It can be cleaned:
You can use bleach on your roof. The stronger the solution, the better it will work. However, the most common suggestion is 1/3 bleach, 1/3 water, 1/3 TSP (detergent). There are also some solutions already prepared. I am most familiar with SHINGLE SHIELD by Chicago Metallic. Check with your local shingle retailer to see if you could get some. I think Chicago Metallic has a website.


Bleach and foliage do not mix well. Be sure to water down all of your plants, grass, shrubs, whatever, both before and after you treat the roof. (Wherever you have runoff)

A common practice is to put the solution in a garden or other LOW pressure sprayer, soak the area needing treatment, wait 15 minutes or so, then rinse it off. It may take more than 1 treatment, depending on how bad the algae is.

You could/should then put a copper or zinc strip at the top of your roof because the mold/fungus/algae WILL come back. The average return after cleaning is around 2 years. This copper/zinc strip will keep the fungus from returning for awhile. There is also zinc strip made by Shingle Shield as well.

Zinc strips and copper strips will perform the same function.

If you want to spend some money, there are businesses that clean roofs and give guarantees.

Good luck.
Old 12-07-03, 12:23 AM
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This is a common question, I wouldn't say make it sticky because then the whole top of the forum would be cluttered with stickys

Everyone is correct in their answers. Just because I feel like typing I will say: You can use a bleach water solution to clean the algae from your roof. This will harm your flowers and bushes etc...

When you have your roof replaced consider an algae resistant shingle. In my area, Chicago, Tamko has it standard in all their shingles. Most manufacturers make algae reistant shingles but not available everywhere.

Keep trees trimmed away from the house. They will drop sap and vegitation on the roof which will cause moss and algae. Also they shade the roof so no sun can penetrate.

On a side note, excessive gravel loss is commonly misdiagnosed as algae because it darkens the shingle in splotches just like algae.

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