Putting on second course over moss/mold covered shingles?

Old 04-22-01, 03:21 PM
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I need to add a second course of asphalt shingles to an old garage with very old (first course) shingles. There is some rotted wood I plan to repair and possibly put a different roof on later. But for now, I'm losing shingles in wind storms and would like to put on a second course of cheap shingles over the old to get a few years out of it.
The question is... the old asphalt shingles have something growing on them. Mold? Moss? I'm not sure. Can I just put the second course over it, or should I clean/strip it first. The garage is not attached to the house, so there are no real health concerns. I'm only hoping to get 3 to 5 years out of it.
Old 04-25-01, 01:08 PM
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Well, if you want 3 to 5 years then leave it alone, as is.
But, It you are going to do the labor, do it right.

Even a cheap shingle put on correctly will last 15 years, or more. Why would you do this for anything less?

As far as the organic matter goes, as long as it is not causing an obstruction, it does not have to be dealt with and can shingled over. It is this kind of organic growth that causes pre-mature death in asphalt/organic shingles.

It is in a protected are or under a tree. Right?

If you are going to tear out and replace some lumber, why not tear off the whole roof anyways? Start fresh.

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