[Greenbuilding] attaching 2" rigid foam

[Jeff Martin]

Reuben,

We've recently installed quite a bit of 2.4" EPS on the interior of a 
cathedral ceiling and some side walls, to reduce thermal bridging. As 
Lynelle noted, the spiral or ring shank nails with plastic washers work 
well for holding the foam in place. We used 3" nails that come 
pre-assembled with white plastic washers, from Ideal Security. You would 
be able to use 2.5" nails. There are also metal washers available for 
the purpose. They're sturdier than the plastic ones, but I haven't seen 
them sold already paired with nails or screws.

When we did our installation, we just used the plastic washered nails to 
hold the foam in place until strapping over it with furring strips (1 x 
3s and 1 x 4s) onto which we installed the drywall. If you're going to 
install the drywall directly on top of the foam board, I wouldn't trust 
the plastic washers to hold everything in place over time. For your 
situation, I think I would use 3" drywall screws to drive all the way 
through to the studs. If you want to use glue, I'd make sure the foam 
was very firmly attached, before gluing the drywall to it (if gluing 
drywall without also using fasteners is allowed there). Maybe a good 
quantity of 2.5" screws paired with the metal foam washers?

Out of curiosity, what kind of glue were you thinking of using for 
attaching the drywall? Here (Quebec), all the fast-grab adhesives I've 
seen are quite expensive and would add noticeably to the cost of 
installing the drywall.

Jeff

On 2016-11-30 5:14 AM, Lynelle Hamilton wrote:
>
> I used a nail with a green plastic ring/washer to attach rigid board 
> here. Worked well.
>
> Lynelle
>
>
> On 2016-11-30 2:50 AM, Reuben Deumling wrote:
>> I got what seemed to me like a great deal on a bunch of 4'x4' panels 
>> of rigid foam at my local Habitat ReStore. It is apparently actually 
>> 1.8" thick and labeled as Polyiso Roof Insulation (=R10.3). The 
>> backing is some sort of fuzzy paper. I was planning on attaching 
>> these panels to the inside of a fiberglass batt insulated 2x4 stud 
>> wall, figuring I'd get a bit more R without the extra thickness of 
>> another stud wall. Are there nails or screws with large washers that 
>> are used with these? Can I glue sheet rock to the exposed face? Or is 
>> there some other method recommended?
>>
>> Thanks for any and all suggestions.
>>
>> Reuben
>>
>>
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