[Greenbuilding] Polyiso strength on roof

[John Salmen]

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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