Wind-driven rain provides the primary external moisture load for exterior walls.Water absorption by the cladding, runoff, and penetration through the cladding or at details determine how a wall system performs. In this paper we describe a new laboratory facility that can create controlled outdoor and indoor conditions and use it to investigate the water management performance of a typical exterior wall assembly. Specifically we have quantified how much water gets past the cladding and hits the water-resistive barrier under particular conditions for a common lap siding.

The CARWASh (Chamber for Analytical Research on Wall Assemblies exposed to Simulated weather) was used to deliver wind-driven rain at two wind conditions and a range of rain intensities. The amount of wind-driven rain was measured on an exposed wall in the CARWASh. Results are presented as a function of wall location, wind speed, and rain intensity. Next, defects were introduced in the lap siding and absorbent pads were placed in the drainage cavity between the cladding and the sheathing to capture any moisture that got past the siding. Results are presented as a percentage of moisture getting past the cladding to incident wind-driven rain and are correlated with wind pressure across the cladding for various wind speeds and rain intensities.

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