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Siding on Framing

My wife and I are renovating a 1920 bungalow where the exterior siding was nailed directly to the framing studs, with no sheathing in between. The siding is in excellent shape and so are most of the framing studs (we've replaced a few termite damaged ones). We're wondering if we should install some kind of moisture barrier from the inside, between the siding and the insulation and drywall. A friend suggested cutting strips of Tyvek, and inserting them between the studs against the siding, then stapling it to the studs, then tucking the insulation in, then the drywall. Is that a good idea? It seems there should be some extra layer of protection between the exterior siding and the interior drywall.

Any input would be appreciated. Thanks!

Re: Siding on Framing

Closed cell spray foam insulation would give both the insulation and the moisture barrier.

Re: Siding on Framing

Thanks. My father-in-law suggested that, but the same friend that suggested the interior Tyvek application said the foam would eliminate all air flow on the inside of the siding. He said having some airflow on the inside of the siding helps prevent rotting and is probably why it's still in such good shape after nearly 90 years. The way the siding overlaps allows some air in behind it. He said the foam would fill that in and cut off that air flow. I'm also concerned about some of the toxic elements in that spray foam. Do you have any other suggestions.

Thanks again.

Re: Siding on Framing

clayj ... there is some merit to the air flow possibly helping the siding to "breath".

While the house wrap does add a level of moisture (water) protection one of it's characteristics is that it breathes which would allow air movement.

At the same time that same air flow is actually detrimental for the R value if you have fiberglass bat insulation since moving air reduces it's insulating performance.


I'm also concerned about some of the toxic elements in that spray foam.

I'm not sure what toxic elements you're concerned with.

One suggestion may be to use sheets of rigid foam insulation since this wouldn't completely conform to the irregular surface of the exterior siding and still allow enough breathing space behind the siding .... then the bat insulation . The rigid foam would provide the moisture , thermo and air break for the bat insulation to be able to reach it's performance.

Just a thought. :)

Re: Siding on Framing

I would think that the moisture barrier for your framing would be more important than air flow. The two go hand in hand though, if the wood doesn't get wet then it won't need to have air flow to dry out and then it won't dry rot as in rot when it dries out.

If you don't find a way to protect the wood from water getting behind the siding onto it then no insulation nor inserted vapor barrier will help.

Re: Siding on Framing

OldGuy1 here;
I think plastic sheeting before the sheet rock should do what you want. You can always go in later and put the spray insulation later, or in places like windows, doors etc. The cost of heating now has pretty much forced the absolute in insulation.

Re: Siding on Framing

Tyvek is designed to be installed on the outside, it passes moisture out but blocks it coming in. Plastic sheeting tacked to the studs before the drywall is installed would work as a moisture bearer. Spry closed cell foam would be the best.

Re: Siding on Framing

Thanks for all your input. Some good suggestions.

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