insulating a house without exterior sheathing or vapor barrier

clintoOctober 6, 2005


I live in Atlanta, Ga and purchased a 1-story 1200 sf, 1930s bungalow on a +/- 2' brick crawl space. It is in need of updating and repair, which I am in the middle of completeing now. I have completely gutted a bathroom and kitchen and rebuilt from the piers up. I have subfloor down but still have exposed stud walls on the interior.

When I did the interior demo work I was amazed to see that the 1x12 exterior siding was nailed directly to the studs on the wihtout any exterior sheathing or vapor barrier. My question is before I install drywall what is the best way to insulate these walls and install vapor barrier if necessary without removing all the siding?

I've looked into open cell foam but my kitchen and bath are too small of a job making it very expensive (no economy of scale) I've also heard of using closed cell foam too but reports are not good with regards to its insulation value. My gut reaction is to just add fiberglass insulation (won't absorb moisture) and then use "greenboard" or some other moisture resistant wallboard or regular wallboard with a vapor barrier installed before hanging drywall. Unfortunately removing the siding is not an option as both are in mid stream of walls and I really don't want to add that to my already long to do list.

Any advice would be greatly appreciated.


Clint Tomasino

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I'm no expert, but I think that's the way most of the older houses up my way were built. Studs and 1x12 boards as sheathing with 1/4 gaps (or more) between. Your siding goes on top of that. I think that I have tarpaper under the clapboard siding on my place. Are you saying that you have 12" wide siding with no tarpaper?

So, don't people put the vapor barrier on the inside of the wall to keep the insulation dry? The outside should be protected from water, but still be able to breathe, right?


    Bookmark   October 6, 2005 at 12:59PM
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Clint, what you suggest sounds good to me. An alternative may be to but up blue rigid foam insulation sheets before the drywall. Studs radiate cold and if you put rigid foam on top of your studs, it's effectiveness is quite a bit higher than bats between wood studs. Cold walls are caused (mostly) by studs radiating the cold. Your order of vapour barrier is correct. Vapour barrier has to be on the warm-in-winter or cold-in-summer side of the insulation.

If your siding is leaking water, then that needs to be fixed and is a different topic than a vapour barrier. You can think of a vapour barrier as "when heating or cooling, a vapour barrier is where the condensation will form".

    Bookmark   October 6, 2005 at 2:05PM
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After living in the house he built in 1950, my dad decided to insulate in the mid-80's. The house was concret block, tar paper & stucco. The inside was plastered. Rather than face the mess of removing the plaster he put the insulation over the plaster and dry walled. He put the furring strips at right angles to the original studs because of the transfer of cold. I don't remember his reasoning but he put a vapor barrier against the plaster & a second one next to the dry wall. The house was wonderful when he finished.

    Bookmark   October 6, 2005 at 2:27PM
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Dear JF,
There isn't any sheathing or tar paper. The 1x12 on the outside is the siding. Does that change any of your thoughts?
Thanks for the help.


    Bookmark   October 9, 2005 at 10:42AM
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I just read this thread and want to add my question to the original.
I am in East Texas. I plan on converting an old woodworking room into a studio. It is 30 years old and was done the same way; i.e., rough plywood sheathing directly over the studs. It is paneled in the cheapest rough particleboard the owner could find (looks like a pile or large wood ships and shreds were simply saturated with resin, then pressed into shape), but the paneling is in good shape and I don't really need to remove it. We though about just adding a vapor barrier, then covering the entire thing with a new layer of paneling or drywall. The questions are: If we add a vapor barrier, where does it go - on the outside of the building with a new layer of siding over that or on the inside with a new layer of paneling over that? And where would the insulation go?


    Bookmark   September 1, 2008 at 5:09PM
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Start a new thread so readers don't have to read through an old dead one to find your question.

    Bookmark   September 1, 2008 at 7:29PM
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Thank you, Mightyanvil. I will do that.

    Bookmark   September 1, 2008 at 9:53PM
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