Watch the video on Exterior Drainage Planes.
The last thing you want to hear is that the paint around a customer's windows has bubbled or the walls are stained—sure signs of water intrusion. Homes built today without a well-designed water management plan can suffer from a variety of durability, comfort, health, and safety issues (ever hear of mold?). A critical component of a comprehensive water management strategy is a well-constructed drainage plane.
A drainage plane is a combination of water-resistant materials like building paper or house wrap, plus a physical space to allow water to flow. The surface tension of water won't allow it to span an area greater than 1/8", so creating a "free drainage" path of 3/8" between the drainage plane (house wrap) and the exterior sheathing will allow water to move unobstructed.
While the specific application of a drainage plane varies depending upon the style of external siding, the basic facts of water movement remain the same. Here are some pointers when creating a drainage plane for the most common types of exterior sheathing.
- Wood siding should be installed over furring strips. This will create a vented and drained space between the drainage plane and the wood siding.
- When using vinyl and aluminum siding, furring strips aren't needed because these types of materials are already engineered for drainage.
- With stucco siding, the drainage plane is created by applying two layers of asphalt-impregnated felt paper to the exterior sheathing. A drainage plane is created between the two layers of felt paper, allowing water to move down and away from the home.
- Brick exteriors require first applying a water-resistant house wrap or building paper to the exterior of the shell, then leaving a 1" gap between the home and the brick exterior. Weep holes and through-wall flashing also need to be incorporated, and special care needs to be taken to ensure that the walls are structurally sound. To learn more about the best practice in creating a drainage plane for brick exteriors, click here.
The walls of the home need the same protection from water intrusion as the roof. Just like putting felt under shingles, the drainage plane must be continuous and free of tears or openings. Be sure to carefully inspect corners, overhangs, and joints, as these are areas where gaps are most likely to occur. For specific information on incorporating the drainage plane around windows visit the Building America website or click here for additional information.
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