Hi, just wandering if it’s normal on a cold flat roof extension on top of the rafters to use 18mm plywood,,, but then use osb on top then grp to finish . Is this a normal thing to do as I thought the 18mm ply would be sufficient to then fibreglass over the top. Why use 11 mm osb on top then fibreglass ,, thanks for any replies .
Plywood then osb
- Thread starter Tiger01
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