Housewrap

Housewrap functions as a weather-resistant barrier, preventing rain or other forms of moisture from getting into the wall assembly while allowing water vapor to pass to the exterior.

Housewrap is installed between the sheathing and the exterior siding, and is used behind vinyl, wood clapboards, shingles or shakes, brick, and other building materials.

In all cases, the housewrap helps prevent water intrusion when moisture in any form gets past the siding and its trim and caulking.

As such, housewrap must be both water shedding and have a high moisture vapor transmission rate (MVTR) to be effective.

[2] It must also withstand abuse during installation, and because housewrap is often left exposed for some time before being cladded-over, it must hold up to wind and resist UV.