Roofing plywood

hrajotteMarch 25, 2013

I need to re-shingle my shed roof, which will also entail replacing 3 rotting plywood sheets.
Is there a particular type of plywood used for roofing, or can I just use standard 4' x 8' panels? (Haven't measured the thickness yet, but looks like 5/8" or 3/4")
Is it acceptable (or desirable) to screw the plywood to the rafters (2x4's) instead of nailing it?
Should there be some type of underlayment before shingling? Currently, the shingles are mounted directly to the plywood, and they lasted 25 years.

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millworkman

CDX or OSB is exterior sheathing normally used. Match the thickness that was used originally (probably 1/2"), then minimum of 15# felt then the roof shingles.

    Bookmark   March 25, 2013 at 9:26AM
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brickeyee

1/8 in gap between sheets.

    Bookmark   March 25, 2013 at 1:16PM
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millworkman

Yes, good point brick and thanks for picking me up!

    Bookmark   March 25, 2013 at 2:45PM
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hrajotte

Many thanks for your advice!

    Bookmark   March 26, 2013 at 7:19AM
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renovator8

The thickness of the sheathing depends on the spacing of the rafters and you didn't tell us that so I would recommend at least 5/8" CDX plywood or Oriented Strand Board.

Asphalt saturated felt (building paper) underlayment once weighed 15 lb per 100 s.f. but it is now much lighter and therefore called No. 15. To match the original standard it is necessary to use No. 30 building paper.

The shingles may have lasted 25 years but obviously they did not protect the sheathing so the design was inadequate possibly because of a low slope. If you want the roofing and sheathing to last another 25 years install an underlayment of self-adhering Ice & Water Shield from Grace without substitution.

    Bookmark   March 30, 2013 at 9:01PM
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millworkman

A little overkill in my mind for a shed, Reno.

    Bookmark   March 31, 2013 at 9:01AM
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renovator8

Making a building last more than 25 years is not overkill to me.

    Bookmark   April 4, 2013 at 10:33AM
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brickeyee

"Making a building last more than 25 years is not overkill to me."

Depends on how large it s.

Not everything needs to have a long life.

    Bookmark   April 4, 2013 at 2:18PM
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