[Greenbuilding] attaching 2" rigid foam

[Topher Belknap]

Greetings,

Firstly, be sure you have the moisture issue figured out.  Polyiso has
low permeability even without foil.  And so, it should be taped, and
considered a vapor barrier.  No wall should have 2 vapor barriers, of
course.

Secondly, I have used plaster washers for screwing in polyiso, and it
works fine (if not perfectly).  Other methods may work better.

Thirdly, R-10 will probably double the insulation value of a 2x4 wall,
perhaps more.

Fourthly, While batting is required to take advantage of any radiant
benefits of foil backed insulation (which if yours have none is moot),
it may not be necessary for construction purposes (or it might).

Thank you kindly,

Topher

-- 
Topher Belknap
Green Fret Consulting
Kermit didn't know the half of it...
http://www.GreenFret.com/

On 11/30/2016 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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