Vapor Permeances, Air Permeances, and Water absorption Coefficients of Building Membranes

Abstract

Abstract Building membranes are integral parts of North American buildings. Some are installed beneath commonly used exterior claddings, brick, and stucco to reduce the risk of water infiltration into the wall systems. Others are used for controlling vapor diffusion though the envelope or as the airtight element of the air barrier system of the envelope. To determine the suitability of a membrane for its intended application, it is necessary to have reliable information on its inherent physical properties. This paper reports the water vapor permeance, the air permeance, and the water absorption coefficient for 18 building membranes that are found in North American markets today. These membranes include paper-based as well as polymer-based materials. The properties reported here show that at the design stage most of the membranes can be considered as the airtight element of air barrier systems and as part of the second line of defense against rainwater penetration. The membranes provide a range of values for water vapor permeance and therefore open up opportunities for a designer to integrate innovative vapor diffusion control strategies for exterior walls and to prolong their service lives.