Problem: Water Penetration Through Siding.
Cause: Lack of rain-screen wall / Incorrect installation of sheathing paper.
- Use rain-screen principles to reduce the pressure difference between the exterior (wind) and the interior of the wall and therefore reduce the amount of water moving into the wall cavity as previously discussed.
Ensure effective drainage of the wall cavity as shown in Figure 28.
Figure 28 - Exterior Wall Pressure Equalization
- Make sure that the wall sheathing paper is properly applied, with no rips or tears and with appropriate overlap of the top sheet over the bottom sheet. The absence of a sheathing membrane or improper installation allows water that has penetrated the exterior siding to move through the wall cavity. Wall sheathing-paper acts as a secondary moisture barrier behind the siding. It should be moisture-resistant but not vapor-resistant, so that water vapor can pass through the wall to the exterior.
Apply the following rules:
- One layer of sheathing paper over wall sheathing will be adequate in most instances. Some builders recommend the use of tow layers of sheathing paper under stucco cladding.
Tar-saturated felts or papers must not be installed as sheathing paper beneath stucco.
- Lap joints in the sheathing paper by a minimum of 4 inches (100 mm). Ensure that the installation of sheathing paper around openings promotes positive drainage down the wall and to the exterior over the flashing as explained further on in this section.