Home>Discussions>EXTERIORS>vapor barriers and vinyl siding
8 posts / 0 new
Last post
Terry
vapor barriers and vinyl siding
Terry

I am preparing to apply vinyl siding over the existing wood siding on a frame house built in the 1950's, the paint was peeling. There is a layer of felt or tar paper behind the existing siding. Should I install a house wrap over the existing siding before applying the vinyl? I would rather not use insulation board as I plan to cover the existing corner trims etc. With aluminum.

Terry
Re: vapor barriers and vinyl siding
Terry

My concern is that if the existing material is considered a vapor barrier and I add a house wrap, wouldn't I be trapping any moisture that may get between the two?

dj1
Re: vapor barriers and vinyl siding
dj1

Quote: "Should I install a house wrap over the existing siding before applying the vinyl?"

The best approach is to remove existing siding. After you do that you will get a chance to inspect the tar paper and replace it, if necessary. My guess is that it has deteriorated since the house was built, to the point of no return. When all siding is off, it will be very inexpensive and well worth it to re-wrap the house.

Fencepost
Re: vapor barriers and vinyl siding
Fencepost

Vapor barrier only goes on the INSIDE of the house just underneath the drywall, to prevent moist air from the interior entering the wall cavity and condensing on the outside wall sheathing during the cold winter months. That can contribute to insulation failure and rot.

The stuff on the OUTSIDE -- housewrap or tar paper -- is a vapor-permeable WATER and AIR barrier. It serves to reduce drafts and helps prevent liquid water that gets past the siding from coming into contact with the wall sheathing and framing and causing rot. Because it allows vapor to permeate, any moisture trapped inside the wall can escape through evaporation.

Terry
Re: vapor barriers and vinyl siding
Terry
Fencepost wrote:

Vapor barrier only goes on the INSIDE of the house just underneath the drywall, to prevent moist air from the interior entering the wall cavity and condensing on the outside wall sheathing during the cold winter months. That can contribute to insulation failure and rot.

The stuff on the OUTSIDE -- housewrap or tar paper -- is a vapor-permeable WATER and AIR barrier. It serves to reduce drafts and helps prevent liquid water that gets past the siding from coming into contact with the wall sheathing and framing and causing rot. Because it allows vapor to permeate, any moisture trapped inside the wall can escape through evaporation.

Thanks Fencepost. That helps tremendously. I don't believe I'll be removing my siding as was suggested earlier. Doesn't even sound like another wrap on the exterior of existing siding would be helpful or advisable as it may trap moisture between existing tar paper and any additional wrap that might be applied?

Mastercarpentry
Re: vapor barriers and vinyl siding
Mastercarpentry

Unless you're removing the old siding, just lay the vinyl on top with nothing in between. If you add anything here and there is still good sealing under the old siding then moisture will be trapped in between, rotting the old siding invisibly till parts of the house start falling off.

Yes, it's extra work and cost but pull the old siding so that you can know that what's underneath it will last and so you can do repairs if that's needed. That will also allow the use of Tyvek which is far superior to the thin tar-paper that was normally used under the wood siding of most houses. It's simply the right way to do things.

Phil

keith3267
Re: vapor barriers and vinyl siding
keith3267

There is a product that you could use, they use it a lot on TOH. Its a screen like material that you would put over the existing siding so that the vinyl doesn't lay flat against it and trap moisture. Its a ventilation material. Without it, your old siding could rot away in some areas.

Terry
Re: vapor barriers and vinyl siding
Terry

Thanks for all the advice!

Sponsored Stories

TV Listings

Find TV listings for This Old House and Ask This Old House in your area.