In a wall assembly with brick exterior and sheetrock interior, where should the vapor barrier be installed?

In a wall assembly with brick exterior and sheetrock interior, where should the vapor barrier be installed?

• A. behind the sheetrock
• B. behind the brick
• C. behind the insulation
• D. top half of the wall only

Answer: (A)

Vapor barriers are placed on the warm side of a wall so interior moisture doesn’t diffuse into the wall cavity. In a wall with brick on the exterior and sheetrock on the interior, the inside is the warm side, so the vapor barrier goes behind the sheetrock, between the studs and the drywall. This setup prevents interior humidity from migrating into the wall cavity where it could condense on cold surfaces like brick or masonry, potentially leading to mold or rot and reducing the wall’s drying ability. It also allows any moisture that does get into the cavity to dry back toward the interior. Putting a vapor barrier behind the brick would trap moisture in the wall assembly and impede drying toward the interior, which is undesirable. Placing it behind insulation or only on the top half would not effectively control vapor diffusion across the full wall.

Vapor barriers are placed on the warm side of a wall so interior moisture doesn’t diffuse into the wall cavity. In a wall with brick on the exterior and sheetrock on the interior, the inside is the warm side, so the vapor barrier goes behind the sheetrock, between the studs and the drywall.

This setup prevents interior humidity from migrating into the wall cavity where it could condense on cold surfaces like brick or masonry, potentially leading to mold or rot and reducing the wall’s drying ability. It also allows any moisture that does get into the cavity to dry back toward the interior.

Putting a vapor barrier behind the brick would trap moisture in the wall assembly and impede drying toward the interior, which is undesirable. Placing it behind insulation or only on the top half would not effectively control vapor diffusion across the full wall.