[Greenbuilding] Polyiso strength on roof

Alan Abrams alan at abramsdesignbuild.com
Mon Dec 8 08:13:54 CST 2014


and now comes Building Green, to out the news on polyiso: that its
performance plummets as the temperature drops...

http://www2.buildinggreen.com/article/polyiso-manufacturers-turn-blind-eye-problems-cold-temperatures?utm_source=BuildingGreen.com%20Mailing%20List&utm_campaign=c7088d50b1-BGB_2014_12_08_members&utm_medium=email&utm_term=0_d558b0594a-c7088d50b1-157062105&mc_cid=c7088d50b1&mc_eid=d0e88c5192

-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 5:53 PM, Sacie Lambertson <sacie.lambertson at gmail.com
> wrote:

> 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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>
>
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