What does housewrap do?
The housewrap, or weather-resistant barrier (WRB), is applied to the wall sheathing before the doors, windows, and siding are installed. It acts as a secondary watershed if any water gets behind the siding, while also keeping unwanted drafts out of the home. But while it’s impermeable to air and liquid water, it’s permeable enough to let water vapor from inside the structure escape to the outside. This keeps moisture from building up in living spaces and wall cavities, where it might condense and encourage mold or mildew. There is at least one sheathing product with a built-in protective overlay that eliminates the need for a separate housewrap.