Water intrusion through walls is the movement of water through the exterior finish into the wall cavity.
While an exterior finish provides the first line of defense against water intrusion, no exterior finish, whether it is brick, stucco, or siding, is waterproof. Brick and stucco are porous. Siding tends to expand and contract due to climate conditions, creating gaps in the finish. Behind the exterior finish, the drainage plane acts as a bulk water management tool that directs all water that penetrates the exterior finish down and away from the home's wall assembly.
The drainage plane
A drainage plane is a layer of water-resistant material that completely covers the home's exterior and integrates with flashing to provide a drainage path from the roof to the ground. When water penetrates the exterior finish, the drainage plane works in conjunction with interconnected flashing to guide water back to the exterior. The drainage plane protects sheathing and framing from getting wet and prevents moisture buildup in exterior wall cavities. A wet wall assembly can lead to peeling paint, wood rot, mold growth, and even structural failure.
Housewrap
In production homebuilding, housewrap has become a material of choice for creating the drainage plane. Housewrap keeps water from entering while allowing water vapor to pass through. Housewrap is designed to keep water out of wall cavities; if a small amount of water does enter, housewrap allows it to dry to the exterior. The key to effective housewrap installation is to provide continuous coverage by lapping each piece shingle style; individual pieces are lapped from bottom to top, so that each succeeding piece overlaps the preceding piece. The wall sheathing and all roofing materials should be installed before the housewrap is applied.
Cause 1:
Lack of a drainage plane
All types of exterior wall finishes allow some amount of water to penetrate through the finish. Without a drainage plane, wall assemblies can get wet, contributing to paint peeling, wood rot, mold growth, and even structural failure.
Solution
To solve this issue, install housewrap. Follow all installation instructions to ensure proper drainage of bulk water away from the home.
Cause 2:
Improper lapping of the housewrap
If the housewrap is reverse-layered—lapped from top to bottom—or installed without enough horizontal or vertical overlap between courses, water can seep behind individual pieces and possibly enter the wall cavity.
Solution
Wrap the home shingle style with housewrap, starting from the foundation and using only manufacturer recommended fasteners. Extend the housewrap past the wall-to-foundation intersection a minimum of 1". Overlap all horizontal and vertical joints a minimum of 6". Tape all vertical seams with construction tape; use the manufacturer's recommended tape.
Cause 3:
Improper fastening of the housewrap
If the housewrap isn't rolled out and fastened correctly, it can wrinkle, creating areas where water may become trapped, instead of moving down and out.
Solution
To help prevent wrinkles, use the manufacturer's recommended fasteners and nailing schedule. Don't use fasteners within 12" of any door or window head.
Cause 4:
Tears, holes, or gaps in the housewrap
Prolonged exposure to wind and debris can damage housewrap. Tears, holes, and gaps create discontinuities in the field of the drainage plane. They give moisture a pathway to water-sensitive sheathing and framing. Material that isn't tightly secured to the sheathing is more likely to tear.
Solution
To avoid these problems, install the exterior finish as soon as possible after housewrap installation. Prior to installing the finish, inspect the housewrap thoroughly. Make sure that the crew repairs all tears and holes with construction tape. In heavily damaged areas, be sure to integrate a new piece of housewrap into the drainage plane, shingle style, to maintain a continuous path for water to drain.
