I am a cabinetmaker who’s just purchased a fixer upper. I have some experience in building/construction but apparently not enough to answer this… or maybe I’d just like some professional/more experienced input from people to clarify my thinking/gaps in my knowledge.
I live in Humboldt County, CA where things get very damp/rainy. I’ve got the walls down to the studs, finished some minor mechanicals, got the floor level as it’s gonna get and am ready to go on framing in the new floorplan. There’s no insulation in the home. It’s got shiplapped siding that’s in OK shape, but daylight peaks through in some spots. I was thinking about rolling strips of tyvek on the inside of the house in the stud bays, adding insulation over it, then drywall. My question is:
Is this a terrible (or even useless) idea? It will not be subject to the elements/liquid moisture, so will it just bead the water vapor and run it to the floor?
Would you use a vapor barrier between the roll type/paper-backed insulation, or nothing? I was just wondering what is the most breathable, effective choice or combo for this endeavor… Thanks for any insights!
Replies
A proper "housewrap" allows
A proper "housewrap" allows water vapor to pass through relatively unabated, while preventing air from passing through, and being relatively waterproof to liquid water. It is NOT a "vapor barrier".
In theory, if there is no liquid water in the vicinity of the housewrap, it behaves pretty much just like plain paper would.
In your situation, I assume you're considering using the housewrap as a wind barrier, and this is not a bad idea. Air sealing the structure better (especially given the poor air barrier presented by the siding) will greatly increase the efficiency of the insulation and make for a more comfortable structure.
Probably the biggest question is how tightly you can manage to do this. If you simply cut strips as wide as the stud bays and hang one in each bay, air will leak around the edges of the strips and severly impact the effectiveness of the scheme. Probably better to run the wrap horizontally, wrapping around the studs, so that there are few seams.
It's not clear whether there's any merit in adding a vapor barrier on the inside (just behind the drywall) in your climate. It appears that you don't have much of an AC season, so it likely couldn't hurt, but it probably doesn't get cold enough to make it necessary to prevent condensation in the walls.
Up here in Seattle area where it is even damper, we put 4 mil or 6 mil straight poly (which IS a moisture barrier) under the drywall, (on teh INSIDE of the house side of the insulation) walls, ceiling, etc. I even like to put a layer of poly between 2 layers of subflooring.
Since the poly creates a tight seal, WA energy codes now require whole house vent fan (or under 1500 sq ft or so) a bath fan on a timer with 3/4" or 1" gap under the bathroom door is specified.
Housewrap or tar paper (I still prefer tar paper) on the outside of the sheathing. What you describe I think is trying tp put tyvek (or tar paper) between the suds against the shiplap. Unless you can get tape to stick to the old studs or tack it in place with furring stips, probably a useless effort.
Better wold be if you do want to have housewrap on the OUTSIDE of the insulation, wrap it into the cavities and up over the studs, likely the only effective low labor effort to do what you desire.