We have just had our two-story new construction remodel in Seattle insulated (hooray!), but the insulators used unfaced batts. Owing to a budget shortfall, drywall is months away. We would like to cover the walls, but have received conflicting information. Should we A) staple up clear plastic, B) Tyvek or similar housewrap, C) kraft paper, D) nothing, or is the right answer something we haven’t thought of? The exterior is plywood with a good covering of 30-pound tarpaper; siding, too, will happen slowly. Thanks for any helpful advice!
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A)
I have no idea of what the right answer is, but I hope you will keep (i) intended activity during that period and (ii) firehazard / flammability in making the decision.
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A, plastic.
You need a material which will prevent moisture from the interior from migrating into the insulation. As moisture migrates closer and closer to the exterior it gets colder (eventually getting as cold as outdoors on the outer surface of the building). Somewhere between the warm exterior and cold exterior it will condense and saturate the insulation. So, to prevent that an impermeable material, like plastic, is fastened to the inside of the insulation under the wall finish.
Tyvek definitely won't work because it is designed specifically to let moisture through. Kraft paper is not very resistant to moisture penetration, though if covered with tar like in some insulation it's better than plain paper.
In the summer you could get by with nothing, but in the winter you'll need to prevent moisture migration. Otherwise, the outer surface of the insuation will get wet, and you won't see it unless you pull the insulation out because it will be on the far side.
The caution about fire is worth heeding. You might be able to get away with it in an unused room, but in an occupied room there is a slight potential that something you do or use could set it on fire.
This may be one of those few times in life where a loan is justified.