# Roof Decking



## Uncle Bob (Sep 30, 2013)

I have been getting inquires about adding a layer of 3/8" osb over lumber roof decking.  The inquires come from what is reported to be a requirement of the asphalt shingle manufacturer that you cannot have over a 1/4" gap bettween the decking boards.  We recently had a hail storm and many of the homes are being reroofed.  My first thought is remove the boards and redeck the roof.  Could roof loads be a factor?  Engineering required to add load?  Has anyone worked with this type problem or request?  How do you handle this type of inquiry?  Thanks, Uncle Bob


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## mtlogcabin (Sep 30, 2013)

3/8" OSB adds about 1.2 psf to the dead load of the roof.

I don't worry about it.


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## David Henderson (Oct 1, 2013)

I agree with mtlogcabin


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## ICE (Oct 1, 2013)

I haven't seen 3/8" used in a new application....it is always 1/2"...it hasn't been an engineering problem.  I have seen plenty of old roof sheathing that is 3/8" plywood.  It is my understanding that the shingle makers require a minimum 1/2" sheathing.


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## Pcinspector1 (Oct 1, 2013)

I agree with mtlogcabin too!

I think GP and LP OSB require a 1/8" gap but not sure if its needed when laying over an existing lumber roof deck. I think the sheets may allow for the gapping and don't measure exactly 4x8.

pc1


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## JMORRISON (Oct 2, 2013)

Put 7/16 over rough sawn 1x on my roof. Nailed through 1x to framing, screwed to 1x where it didn't hit.  Less dead load than a layer of roofing. The space as per manufacturer to avoid joints from raising due to expansion


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