[Greenbuilding] Polyiso strength on roof

[Sacie Lambertson]

Recommend highly staggering the EPS on the roof, using the foam
sealant/glue John mentions AND covering all with thick layer (s) of felt.
We have had a condensation problem with a similar combination (metal roof
attached to straps etc).  I am pretty sure it is because the foam was not
staggered and or sufficient foam/glue was not used in all the nooks and
crannies.  Needs some real hands on supervision and frankly better if the
details are handled by you rather than the construction people.

Plywood not necessary.

We're in NE Kansas.  Lots of wind.

Sacie

On Sun, Dec 7, 2014 at 9:03 AM, John Salmen <terrain at shaw.ca> wrote:

> 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
> <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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