Hygrothermal Analysis of Double-stud Wood Walls in Non-residential Construction

The R.W. Kern Center is a 16,940 square-foot mass timber-structured institutional building located on Hampshire College’s campus in Amherst, MA. It is the 17th certified Living Building in the world. The focus of this work is the examination of the use of Double Stud Wood Wall (DSWW) construction, an atypical system in an institutional building of this scale, Light-Frame Steel Wall (LFSW) being the typical strategy.

The success of this system, in non-residential construction, with the increased internal loads as compared to residential buildings, the associated and elevated concern of high R-value walls, low temperatures at the exterior sheathing, and subsequent susceptibility to moisture-related problems from condensation due to mass transport and mass transfer via interior moisture migration through the assembly within low dewpoint probable temperature periods of the year is of interest.

During the Kern Center’s design (September 2013–September 2014) and construction (October 2014–April 2016), although there existed a substantial body of information referencing the control of air and vapor movement as related to humidity levels within wall assemblies using assorted membranes, tapes, caulks, and gaskets, there was not a definitive solution to ensure the wall assembly’s performance and durability.

In depth examination of the DSWW strategy in the Kern Center was made possible by the availability of three years of post-occupancy data collected by multiple sensors on all cardinal elevations. This allowed the evaluation of condensation risks and assembly drying potential throughout the year based on sensor data of exterior weather and interior conditioned space sensible air temperature (T), dewpoint air temperature (DP), relative humidity (RH), and absolute humidity (AH), as well as sensor data from within the assemblies, i.e., sensible and DP temperatures, RH, AH, and moisture content (MC).

This study provides unique and valuable information for researchers, designers, and constructors concerned with best practices for moisture management in Double Stud Wood Walls (DSWW) in non-residential construction while targeting low embodied carbon footprint goals.