[Greenbuilding] Polyiso strength on roof

[Alan Abrams]

<I plan to fill the cavities between the rafters with cellulose so the
polyiso would not be exposed. Just another fact...not sure it addresses
your point.>

Bill--not unless the cellulose is labeled for that application. however, 1
1/2" of mineral fiber would also do the job.
-aa

Alan Abrams

*certified professional building designer, AIBDcertified passive house
consultant, PHIUS*
*certified passive house builder, PHIUS*
cell     202-437-8583
alan at abramsdesignbuild.com
HELICON WORKS *Achitecture and Education*
<http://www.heliconworks.com/index2.html>

On Sun, Dec 7, 2014 at 1:53 PM, Bill Allen <bill.allen at verizon.net> wrote:

> Steve,
> I am suggesting a sip type assembly only without the bottom plywood.  The
> insulation will rest on the 1x2 nailers. This is the inverse of what you
> discribed.
>
>
> Sent from my cell phone
>
>
> -------- Original message --------
> From: Steve Houlihan <sho11 at comcast.net>
> Date:12/07/2014 1:28 PM (GMT-05:00)
> To: greenbuilding at lists.bioenergylists.org
> Cc:
> Subject: Re: [Greenbuilding] Polyiso strength on roof
>
> There are many thousands of roofs out there with a layer of plywood then
> rigid foam above.  I'm under one right now.  I have never seen the Building
> Department to have a problem with this.  I suggest you check with your
> local jurisdiction to be sure.
> I don't see any difference to this from using SIPS on the roof.
>
> Steve Houlihan
>
> On 12/7/14 10:08 AM, John Salmen wrote:
>
>  Ply sheating wouldn’t qualify as a barrier. Glas mat roofing board would.
>
>
>
> *From:* Greenbuilding [
> mailto:greenbuilding-bounces at lists.bioenergylists.org
> <greenbuilding-bounces at lists.bioenergylists.org>] *On Behalf Of *Alan
> Abrams
> *Sent:* December-07-14 9:55 AM
> *To:* Green Building
> *Subject:* Re: [Greenbuilding] Polyiso strength on roof
>
>
>
> 'nuther factor is the prohibition against exposed plastic foam in the
> attic. even foil faced polyiso does not fulfill the requirement.
>
>
>
> -aa
>
>
>   Alan Abrams
>
> *certified professional building designer, AIBD certified passive house
> consultant, PHIUS*
>
>
> *certified passive house builder, PHIUS *cell     202-437-8583
> alan at abramsdesignbuild.com
> HELICON WORKS *Achitecture and Education*
> <http://www.heliconworks.com/index2.html>
>
>
>
> On Sun, Dec 7, 2014 at 12:44 PM, Ron Cascio <roncascio at verizon.net> wrote:
>
> 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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