Re-roof sheathing question
Dadams
| Posted in GBA Pro Help on
Aged and damaged shingles to be replaced prior to PV install. Discovered decking is only 3/8 plywood, with soft flexy areas and visible Hi/Lo wave on West pitch. 2X rafters on 12’s and some 16 with H clips. Prior mold remediation, hip roof. Ridge and soffit venting will be maximized. Attic is fully air sealed and now R50. My thought was to reinforce w/ 1/2 in CDX overlay. Roofer A dislikes 2 layers: leave it alone or replace with min 1/2″. B suggests add 5/8, doesn’t seem to care / my option whether to overlay or remove 3/8″. What say we, please?
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Replies
Dadams,
Don't re-roof on 3/8" plywood. The only reasons not to use a second layer are if:
- There is enough damage on the existing layer you have to replace so many sheets of it prior to the overlay that you would have been better off just to remove it all.
- The roof can not support the additional dead-load of two layers.
- The existing sheathing is so wavy there will be deep voids between the two layers, which can cause moisture problems.
Thank you, Malcolm. Always a calm wise voice here, you are highly appreciated.
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Dadams,
Cheers - and good luck with your project.
Malcolm's advice is spot-on!
Remove the clips before you add a layer of sheathing. If there is variability in the roof, 5/8" tongue and groove Advantech will insure the edges of the deck align, otherwise 1/2" will suffice.