Roof Decking

[Uncle Bob]

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

 

[mtlogcabin]

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

I don't worry about it.

 

[David Henderson]

I agree with mtlogcabin

 

[ICE]

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.

 

[SCBO1]

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

 

[JMORRISON]

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