# drywall, hung, interior 1" rigid insulation?



## Lar77 (Mar 28, 2016)

I am on a building committee for my church, the architect wants to use 1" rigid foam insulation on the interior side of the outside wall. This project is in Wisconsin, we are using 2x6 studs, w/batt insulation, exterior building wrap over 5/8" o.s.b. and an interior vapor barrier.

My concern is nail pops if the foam is screwed tight and under pressure and in time expends and creates the nail pops or worse.

Not mention the added difficulty of hanging the drywall over the rigid foam, which could add to the cost of hanging the drywall.

Any feed back is welcome, thanks in advance.

Larr77


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## MrWillys (Mar 10, 2014)

You could run 1" Z-furring 24" oc applied perpendicular to the framing members and then stand the board up on the walls. If the foam is 1" then I'd order the z-furring 1 1/8". This will achieve the insulation goal and provide positive attachment for the drywall.
Also, your insulation requirements most likely are in excess of the 2x6 stud wall and the foam is needed.


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## Lar77 (Mar 28, 2016)

Thanks Mr Willys,
I follow what you are telling me, with using the z-furring strips.

Follow up question to your response; If no furring strips are used would you recommend not attaching the drywall directly over top of the 1" rigid foam?

Forget the 1" foam altogether, would that be the way the better alternative? We would meet the insulation requirements without the 1" rigid foam.

Lar77


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## MrWillys (Mar 10, 2014)

Clearly the Architect thinks it's an acceptable method and most likely documented in your region. Where I'm from we put it on the outside and call it EIFS (exterior insulated foam system). You're paying someone with an 8 year degree so maybe he deserves more trust. I have never done what you're asking and it bothers me a bit to in theory. I guess it's not much different than going over the top of sound board though?


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## endo_alley (Nov 2, 2013)

Why not spray foam insulation into the stud cavities?


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## Lar77 (Mar 28, 2016)

Thanks guys,
We are going to have spray foam priced out as well as batt insulation.

Regarding the Architect; I am questioning his application with the 1" rigid foam under the drywall with no furring strips. Do not care for the look of EIFS for this application.
Don't know if anyone even in Wisconsin would hang drywall over 1" rigid foam on 16 ft. high sidewalls. I don't about the 8 years of education either, 4 years for sure and than 5 years working experience before they can take the test to become licensed. Just because some has a degree and a title doesn't mean they can do whatever on a project I am helping pay for and responsible for as a member of the building committee. If this was done on another project with no issue that is something all together different.


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## P.E.I.Taper (May 4, 2015)

I finished a house where the used that insualtation on the interior walls years ago. The guys hanging the board hated it. Which meant I had a harder time covering the screw misses. Weather or not it held up as well, I do not know.


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## endo_alley (Nov 2, 2013)

In my personal home, I admit (20 years ago) that I used R39 batts in the rafters, and then 2" blue foam insulation over the bottom of the rafters to give me another r-9 or so. I hung the drywall over the foam with 3 1/2" screws on the high ceilings. It was truly a pain in the butt to hang. But I haven't noticed any screw pops yet. It would be much easier to just spray the foam. There are probably other cheaper spray in insulation products that would work fine also.


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## Canadian_wood (Jan 22, 2017)

On rigid foam we always use 1×4 strapping either on top or 'let in' the foam


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## Canadian_wood (Jan 22, 2017)

Spray foam is very expensive and the longevity of the product relies a lot on the skill and knowledge of the inslator. It is rendered useless by even the tiniest of gaps, crushing or seperation from the substrate. In areas with extreme differences between outside and inside, sudden temp swings, or framing that may flex more (ex. Species of wood available, age) there may not be ideal conditions for spray foam in the long run. Architects tend to be very thorough when addressing the bulding envelope. It would be wild to assume he doesn't know the pros and cons of spray foam.


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## endo_alley_revisited (Aug 9, 2016)

Canadian_wood said:


> Spray foam is very expensive and the longevity of the product relies a lot on the skill and knowledge of the inslator. It is rendered useless by even the tiniest of gaps, crushing or seperation from the substrate. In areas with extreme differences between outside and inside, sudden temp swings, or framing that may flex more (ex. Species of wood available, age) there may not be ideal conditions for spray foam in the long run. Architects tend to be very thorough when addressing the bulding envelope. It would be wild to assume he doesn't know the pros and cons of spray foam.[/QUOTE
> 
> 1. We have an R50 requirement for all roof insulation. Spray foam or foam roof panels are the only way to achieve this. From what I have seen when remodeling older homes that were sprayed with foam in rafter or wall stud cavities, once it is sprayed, nothing moves. It would take a powerful earthquake to get the foam to move. It sticks to wood soundly. So any very minor shrinkage of wood would pull at the foam. And plywood or OSB does not shrink. Foam insulation does not readily delaminate from wood or anything else.
> 2. Also, Rigid foam insulation could be applied over the external sheathing, and under the building finish, regardless of what that is. It needn't be EIFS. You can even apply conventional stucco over rigid exterior insulation if you so choose.


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