Over the past several decades, advances in the application of polymers brought new polymeric water-resistive barriers with a wide range of vapor permeability to market, commonly referred to as "breathable" housewraps. However, at this time there is virtually no guidance available regarding the selection of the optimum vapor permeability of such membranes under specific conditions.

This paper evaluates the impact of various water-resistive barriers with a large range of vapor permeability on the hygrothermal performance of different wall assemblies. The information enables designers to select products with the most suitable vapor permeability for particular geographical locations and construction conditions. Variations in boundary conditions included climatic conditions (seven climatic locations), cladding type (three-coat stucco, manufactured stone, cement board, brick), and type of WRB (low versus high vapor permeability) deployed. The results for the performance of the wall systems are presented in form of a mold index.

Presented at Thermal Performance of Exterior Envelopes of Whole Buildings XII, December 2013