Home>Discussions>EXTERIORS>Washing roof, mildew etc.
5 posts / 0 new
Last post
Washing roof, mildew etc.

I would like to clean my roof for two reasons, nearby trees have created a lot of shade and mildew, two, I will probably paint the shingles in the next year or two.

So, my question is what type of soap, solvent. I expect bleachwater would do it, but I am concerned about the run off.

Re: Washing roof, mildew etc.

If you trim the trees and increase air flow the mildew will die on its own.

If you don't trim the trees the mildew will return.

Re: Washing roof, mildew etc.

I've had good luck with applying bleach with a garden sprayer. 100% bleach - a gallon for about a square (100 sf). Spray enough but don't let the bleach run. Don't slip and fall off the roof.
The Mold will be gone in 20 minutes.

Re: Washing roof, mildew etc.

I have used a product called "Jomax" for over 30 years. It is very effective at killing mold, mildew and algae at a much lower concentration of bleach. A quart bottle of the Jomax concentrate goes in a five gallon pail with 3 quarts of household bleach and four gallons of water. It can be sprayed with a garden sprayer. The surface should be kept wet with the solution for several minutes, and then rinsed off.

Wooden roof shingles become immediately and unbelieveably slippery when wet. I always carried a pair of strap on shoe cleats in the truck for such occasions. Mere tennis shoes or such just don't hack it.

There are also high pressure power washing injector tips available. This will allow you to spray bleach out about 20 feet, often avoiding having to get on the wet roof at all. I would siphon directly out of the bleach bottle to which I had added a big slug of Ivory Dish Washing Soap. The Ivory was a nice mild soap which aided in cleaning, but its main purpose was to indicate where I had sprayed with bleach by virtue of the visible foam. A zero tip would then spray water high up on the roof without doing damage when sprayed from a distance. The water would then naturally drain down the roof.

Re: Washing roof, mildew etc.

Here is what I like to do:
Option 1: Use 1/4 to 1/2 cup bleach to 1 gallon to water and use a garden spray to spray the area. This will give you just enough bleach to kill the mildew and you won't have to worry about staining your roof or killing the plants below.

Option 2: Use Shingle Shield. It is a premade mixture that you use in a garden spray that kills mildew on your roof.

When you are done look into getting a zinc strip for the peak of your roof. Shingle Shield also makes zinc strips.

When you put a zinc strip at the top of your roof, as rain hits the strip and washes down it kills the mildew it runs over. This keeps the mildew from coming back.

I hope this helps.

Sponsored Stories

TV Listings

Find TV listings for This Old House and Ask This Old House in your area.