[Greenbuilding] Polyiso strength on roof

[Clarke Olsen]

It does sound like too much plywood. You should use 5/8" plywood for your one layer: it is rumored to have twice (exaggeration?) the nail holding of 1/2".
Clarke Olsen
clarkeolsendesign.com
373 route 203
Spencertown, NY 12165 
USA
518-392-4640
colsen at taconic.net




On Dec 7, 2014, at 10:52 AM, Bill Allen <bill.allen at verizon.net> wrote:

> Hi all
> I am about to reroof my 1926 colonial and am looking to also insulate per the BSC "deep energy retrofit" plans consisting of plywood sheathing, 2 layers of 2" polyiso, another layer of plywood, then roofing (in my case, standing seam metal roofing).
> The original roof was wooden shingles that are still in place with 2 layers of asphalt on top. Also still in place are the nailers for the wood shingles...roughly 1x2s, 5.5" on center across the rafters.
> 
> My question is: if I leave the 1x2 nailers in place during the demo can i exclude the first layer of plywood and install the polyiso directly on the nailers? It would then have plywood on top, secured with long screws into the rafters. Less material and less cost.
> 
> Thanks for any thoughts/comments.
> 
> 
> Sent from my cell phone
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