Vapor Barrier or Not?

[laynes69]

We are gettin ready to put an addition on our home. The old laundry room was in need of replacement due to mold, rot, etc. Anyhow, the last time we had an energy audit done, the people running it said no to vapor barriers. I was always taught it was required in our zone (5 I believe) in Ohio, due to some cold winters. I decided on re-using the old siding shingles, not only to match the current home, but save money. The 1/2 osb will be covered in 30# felt and the shingles will go over this. The walls will be 2x6" and I'll concentrate on airsealing before insulating with batts. I almost went with housewrap, but decided against it for there's too many unknowns, and the original Dutchlap siding under the felt was in perfect condition. Do I need a vapor barrier behind the drywall? Thanks.

 

[Hogwildz]

Insulation with the paper backing should be all you need before the drywall is installed. Paper on the interior side. The Dutch lap under felt? Is that original wood siding, which was covered by felt and other siding?
That would be at least part of your problem with the mold/moisture issues. 30 lb tar felt will not let things breath as well as house wrap will.

 

[pyroholic]

If your doing this with a permit I think they would make you use house wrap. They surely do in MI, even on non-living spaces. Think gables, garages, any exterior sheathing ( other than the roof of course). Regardless house wrap is a good thing. Certainly your call, but I would use the wrap.

 

[brian89gp]

Have you checked your local building codes to see if they have anything to say about it? For a while it was always assumed that everybody needed a vapor barrier, but as your energy audit person said that assumption is no longer always considered true.

One important thing, especially with wood lap siding, its hard to have mold and moisture damage if you have a wall that has a method to dry out.

 

[laynes69]

The mold and moisture problems was due to a flat roof that has leaked on and off over many years. To complicate matters, there was a false ceiling added in the laundry room that hid many problems. That portion is a single story after thought, with a flat roof. The rest of the home had the tar paper and shingles removed to expose the original dutchlap which is as good as new. I think the asbestos shingle was placed on the home in the 50's, so the felt paper isn't a problem. We don't have inspectors in our area, and the local company that did the energy audit was the electric company, not builders. Tyvek seems to be a decent product, but can also have complications if water gets behind it. I want to replace with what was there, but the issue again is if a vapor barrier is needed. Other than the laundry room where leakage had occured, everywhere else on the home that leakag had occured, was fine. The house is a mid 19th century Victorian, so its not a modern home.The home originally had dutchlap wooden siding, which was covered in the 50's with tar paper and asbestos shingle.

 

[begreen]

A thermal break may have higher value. Sheething the exterior with foam board or using staggered 2x4s to create an 8" insulated cavity are a couple approaches to achieve this. As point of reference, my BIL built his place in the early 1980s using staggered 2x4 construction and an inside vapor barrier that is tightly sealed at all openings, either taped or caulked. They consistently heat their house in a colder climate (mid-NY), yet use less wood than us to heat, about 2 cords.

There is a lot of good information on the Building Science website. This link will get you started:

(broken link removed to http://www.buildingscience.com/resources/vapor_barrier_code_changes)

 

[semipro]

No vapor barrier is needed behind the drywall for your climate.
The roofing felt should work well for your situation. There is some evidence that the tannins in wood cladding/shingles attacking the integrity of synthetic house wraps like Tyvek. The vapor permeability of felt is similar to that of housewraps.
What I don't like about roofing felt is that I find it much harder to air seal. Just overlapping the layers doesn't create a good seal. I haven't found a tape that works on it nearly as well as the the tapes made for Tyvek/Typar. Even the self adhesive flashing products don't seem to stick well to roofing felt. I've used asphalt based caulks with limited success.

 

[laynes69]

The new build will be a million times tighter than the old room. It was paneling over lathe boards with rotten studs. Much worse than I thought. My thoughts exactly on the air sealing from the felt, but I will caulk and make things tight before drywall. Still use kraft faced batts right? Since its a vapor retarder and not a barrier.

 

[semipro]

The kraft paper is a vapor retarder as you said and shouldn'tt create any problems. It does make installation of the insulation easier and cleaner looking. Staple to the fronts of studs, not sides.
Good batt insulation is not easily accomplished. Even pros frequently do it wrong. Its worth watching a few videos on it.

 

[laynes69]

Installation isn't a problem, Dad had an insulation business. I always face staple, and If required custom cut the batts to fit without stuffing or compression. I watched a house flipping tv show and the fiberglass insulation was stuffed into the walls like crumpled newspaper. Basically a waste of money. A little extra time makes a big difference. The addition will be roughed in, and I will finish with siding, insulation, electrical, plumbing and ductwork.

 

[Hogwildz]

I even tapes the seams on mine