When you build a house (or an addition), you generally apply sheathing to your wall studs, and then put your siding material over top of that. Another method is to install polystyrene installation over thinner (2x) walls, which helps to improve the overlap of insulation. But either one of these techniques will still allow air to infiltrate the walls. Gaps between the sheathing, or between the insulation, leave lots of room for wind to find it’s way inside.
Not to mention water. Even if your house is vinyl sided, wind-driven rain will find a way behind the siding.
Now, when wind enters the house, it doesn’t just cause cold drafts. It increases the air pressure inside, forcing out the air you’ve heated (or cooled in the summer).
And that’s where housewrap comes in. Housewrap is a thick, paper-like product that resists air and water coming from the outside, yet allows moisture vapor to breathe through it from the back. By wrapping your entire house in housewrap, you’re putting up an additional line of defense against the weather.
In addition to sealing up gaps between sheathing, housewrap provides important protection around windows and at the sill plate.
The wrap should be continuous, obviously. That is, it should overlap, so the entire exterior’s covered, and it should also be applied so that the layers higher up overlap layers lower down, so that moisture is shed. Special manufacturer-approved tape seals up the seams.
Next time, we’ll look at some installation tips.