Which layer lies directly outside the insulation in the exterior wall build-up?

Which layer lies directly outside the insulation in the exterior wall build-up?

• A. Wood frame
• B. Plywood sheathing
• C. Building paper
• D. Interior wall finish

Answer: (A)

In an exterior wood-frame wall, the insulation fills the cavity between the studs, which form the structural skeleton. The wood frame sits directly adjacent to the insulation as you move from the interior toward the exterior, making it the layer immediately outside the insulation. Beyond that boundary come the exterior sheathing (plywood or OSB), then building paper, and finally the exterior siding. So the wood frame is the closest successive layer outside the insulated cavity. Plywood sheathing serves as the outer structural skin, building paper acts as a moisture barrier, and the interior wall finish is on the inside—farthest from the exterior.

In an exterior wood-frame wall, the insulation fills the cavity between the studs, which form the structural skeleton. The wood frame sits directly adjacent to the insulation as you move from the interior toward the exterior, making it the layer immediately outside the insulation. Beyond that boundary come the exterior sheathing (plywood or OSB), then building paper, and finally the exterior siding. So the wood frame is the closest successive layer outside the insulated cavity.

Plywood sheathing serves as the outer structural skin, building paper acts as a moisture barrier, and the interior wall finish is on the inside—farthest from the exterior.