In alt.home.repair, on Sun, 16 Feb 2020 17:29:10 -0500, Clare Snyder
wrote:

On Sun, 16 Feb 2020 12:43:46 -0500, micky
wrote:

In alt.home.repair, on Fri, 14 Feb 2020 09:23:09 -0500, micky
wrote:


I need a new roof, or a repair of the old one.

Another question has come up.

It seems the original roof had 3/8" plywood and one roofer wants to
patch it with some sheets of 1/2" plywood, which he says is better.

The other roofer says it will leave valleys that water will collect in,
and that's bad.

I can certainly see if the thicker stuff is below the thinner stuff,
there would be a 1/8" dip, at an angle** which makes the dip a little
less, and a bit of water would sit there until it evaporated or sunk in,
but isn't the roof supposed to be waterproof?

**Roof is 2:5 I think. Prefab trusses.

Will every replacement sheet of plywood be noticeable from the street,
two stories down, because plywood is 1/8" thicker. Should they use
3/8th to patch 3/8ths?
Thicker above thinner won't cause an issue, but you WILL see it from
the street with 3-tab shingles. With "high def" architectural shingles
the line will virtually dissapear with the new roof installation - but
MAY telegraph through over time.
A roof is supposed to be "highly water resistant" and "weatherproof"
but don't necessarilly count on it to be "waterproof" as in being able
to hold standing water like a pail or a swimming pool.

How many sheets of plywood would it take to do the complete street
side of the roof?

15 at $65/sheet for CDX plywood. $975

Street side, that is, just for appearance?

I'd be sorely tempted to replace the whole face
with 1/2 inch. I know I'll never put 3/8" plywood - or anything other
than fir - roof decking on anything bigger than a dog-house again
after the issues Ihad on my shed roof.

What issues on the shed?.

Here it did pretty well the first 39 years.