Here are all of the basics on commonly used drainage plane materials and their properties.
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Despite a homebuilder's best efforts, some water will penetrate the first line of defense, the exterior finish (siding, brick, stone, or stucco), and may also enter through gaps around windows and doors. When wood framing gets wet and is unable to dry, over time, it can rot and cause structural damage, possibly causing the home to settle or shift. In addition, when wood framing is wet, mold can grow on it. What's more, visible damage from moisture (like peeling or bubbling paint) isn't pretty, and reduces the value of a home.
It's important in the framing stage to implement a drainage strategy to protect the vulnerable wood shell of the home by providing a barrier to water and draining the water away from the exterior of the home. The first part of this strategy includes a continuous roof and wall drainage plane. Drainage plane materials fall into four general categories: felt building paper, house wrap, thin structural sheathing, and rigid foam sheathing.
No matter which material a builder uses, the drainage plane must be continuous from the roof to the ground, which means that joints and corners should be covered, and special materials called flashing used around window and door openings.
The following are the commonly used types of drainage plane material and their basic properties.