Cladding Systems

Effect of Cladding Systems on Moisture Performance of Wood-Framed Walls in a Mixed-Humid Climate

A 22-month field investigation of nine different north- and south-oriented wood-framed wall assemblies was conducted to determine the moisture performance of various wall construction types, most of which incorporated absorptive cladding. The study was conducted on the campus of the National Association of Home Builders (NAHB) Home Innovation, in Upper Marlboro, MD, 20 miles east of Washington, DC, in a mixed humid climate. Moisture content of the sheathing and wall cavity temperatures were measured at various points in each wall section. The primary performance measure was moisture content of the wood-based structural sheathing.

Under normal weather exposure, the studs and sheathing in all walls investigated remained well below 20% moisture content. South-facing walls with direct solar exposure resulted in dryer sheathing. Walls with non-absorptive cladding (vinyl siding and insulated vinyl siding) had among the lowest sheathing moisture contents recorded in the study; this was the case for walls that faced either north or south. Low sheathing moisture contents were also recorded in the south-facing walls with (a relatively dark color) manufactured stone cladding and in the south-facing wall with brick veneer cladding.

Controlled injections of water behind the cladding indicated that some walls were less able to drain (or otherwise dissipate) the injected water than were others. Stucco-clad walls with only one layer of water-resistive barrier (WRB) showed the least ability to dissipate injected water. Walls with manufactured stone cladding (which incorporated two layers of WRB) showed a lesser ability to dissipate injected water than walls with most of the other cladding systems, but greater ability than stucco-clad walls with a single layer of WRB.