[Greenbuilding] Polyiso strength on roof

Bill Allen bill.allen at verizon.net
Sun Dec 7 12:50:03 CST 2014


John,
I did not mention the air, water and vapor barrier the metal roofing contractor spec'ed on top of the plywood, under the metal...titanium psi-30 I think it is called.
The fastening system is typical staggered hidden clips for the male side of the panel that the femail side of the next panel snaps over.
Why Epson over polyiso?
Thanks

Sent from my cell phone


-------- Original message --------
From: John Salmen <terrain at shaw.ca> 
Date:12/07/2014  1:03 PM  (GMT-05:00) 
To: 'Green Building' <greenbuilding at lists.bioenergylists.org> 
Cc:  
Subject: Re: [Greenbuilding] Polyiso strength on roof 

I would strongly recommend eps rather than polyiso for the roof insul. There are a number of benefits you can research. 2” foam can span the 5.5 centres but I would bond the staggered foam layers together using some foam adhesive (spray poly foam works well). Depending on the type of metal roofing (fastening) it could be laid directly on the foam (with a wrb) eliminating the ply layer. Metal roofs are very prone to condensation inevitably wetting the sheathing so the ply is a weak component. If ply is used a a very well applied wrb is crucial (membrane). The ply is really just there for fastening so if a z strip or other fastening system could be used it would minimize material in the assembly.
 
John
 
 
From: Greenbuilding [mailto:greenbuilding-bounces at lists.bioenergylists.org] On Behalf Of Ron Cascio
Sent: December-07-14 9:45 AM
To: 'Green Building'
Subject: Re: [Greenbuilding] Polyiso strength on roof
 
Sounds good to me.
 
Ron
 
From: Greenbuilding [mailto:greenbuilding-bounces at lists.bioenergylists.org] On Behalf Of Bill Allen
Sent: Sunday, December 07, 2014 10:52 AM
To: Green Building
Subject: [Greenbuilding] Polyiso strength on roof
 
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
< dy>
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