Home Repair

Trouble killing moss on my roof

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From an email received:


I am having trouble with moss on a steeply sloped roof. and have not had much success on ridding myself of it by using a mixture of 50/50 water and bleach.... I am afraid that if I make it stronger, I might possibly bleach the roofing material.... is there any safer or more sure way of getting rid of this for a DIY'er?

I removed several trees from the property near the house, so that it gets a full day of sunshine, and believe that was the source of the moss.

I shall be so greatful for any help you can give me... thank you,

D.C. B.
Hello D.C.

I would suggest that you again scrape the moss (gently!!!) from the roof, then again try to kill it with a liquid solution as you've tried (protect the shrubs under the roof!) and then install a zinc strip along the length of the roof up near the ridge (close to the top). You'll have to lift a row of shingles and install the strip; being sure to carefully seal around any nails you install, then re-seal or glue down the course of shingles that you've lifted.

The zinc should provide many years of protection.

As for a solution to use, it seems that your 50/50 solution of bleach to water is quite highly concentrated. Some sources recommend a slightly different mixture of 1 cup liquid chlorine bleach, 1 cup of laundry detergent and 1 gallon of hot water.

Spray it on with a garden sprayer, allow to sit for 15 or twenty minutes then wash off. Be careful!!!!! Any place that has gotten wet with the solution will bleach your clothes if you touch it before you further dilute it by washing it off with your garden hose, and it will be VERY SLIPPERY. Also, don't forget your eye protection when working with and around that bleach solution.

If you don't like the thought or the curb appeal of the zinc strips, there are some chemicals that you can apply twice a year that will keep the moss from returning, and they may be more effective than the strips over the long term, but vigilance and discipline are a must.

Feel free to ask any further questions about this right here! Just follow the link above then click on reply.
I have been told that bleach can damage composition roofing as it dries out the roofing material and can lead to pre-mature leaks.
Also, avoid the new laundry detergents. The old ones had phosphates,
which did the job on moss, but was very bad for the environment. The new ones have degreasers that eat away at the shingles.
Zinc sulfate, while a naturally-occurring mineral, can pollute rivers and
streams and is toxic to aquatic animals. Zinc strips have disadvantages. Even though each strip releases a small amount of zinc,
the cumulative effect of widespread use will still
pose a pollution threat to rivers and streams.

Oxygen based cleaners are the best bet for killing the moss.
There are various products, but are based on Hydrogen peroxide.


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