Weather-Resistive Barriers

How to select and install housewrap and other types of weather-resistive barriers

Introduction
Weather-resistive barriers are a part of exterior wall systems that protect building materials from exterior water penetration. They perform like a shell for buildings—liquid water that has penetrated the exterior finish does not pass through, yet water vapor can escape. By keeping building materials dry, a weather-resistive barrier improves building durability, decreases maintenance costs, and reduces the risk of moisture-related problems such as bugs, mold, mildew, and rot. Some weather-resistive barriers also reduce air infiltration, cutting utility costs and increasing comfort.

Types and Costs of Weather Resistant Barriers
Building paper is a traditional paper sheet or felt material that is asphalt coated or impregnated to increase its strength and resistance to water penetration. It is primarily employed to protect against moisture as a drainage layer. Housewrap refers to spun-plastic sheet materials that are wrapped around a house to protect against moisture penetration. If properly sealed, housewrap can also serve as an air retarder to reduce infiltration. In some wall systems, sealed waterresistive sheathing such as rigid foam board can serve as the weather-resistive barrier, eliminating any need for building paper or housewrap. Building paper typically costs about $300, material and labor, to cover a 2,500-square-foot home. It usually comes in a 3-foot roll that one person can install. Housewrap costs about $450, materials and labor, for the same size house. While it is available in 3-foot rolls, rolls are usually 9-feet wide and require two people for installation.

When and How to Use Weather Resistive Barriers
As part of a whole-wall design, weather-resistive barriers need to be integrated with other wall system components, including structure, insulation, vapor retarder, air retarder (if separate), and flashing systems. A comprehensive approach to water management prevents water from reaching the sheathing or framing. Primary water management strategies include water-shedding characteristics that include overhangs and exterior claddings. Secondary (redundant) water management usually employs a weather-resistive barrier to protect the sheathing and framing from moisture damage.

A weather-resistive barrier is a drainage plane. It allows water that has penetrated past the siding
to drain away from the wall system. Building paper or housewrap is usually used to form the
barrier. Attaching siding to furring strips provides an air gap between the siding and weather-resistive barrier that improves drainage and addresses related moisture issues.