Moisture Performance of Walls in Energy Efficient Homes

Published Tuesday, September 15, 2015

Recent changes in the minimum energy code (2012/2015 IECC) significantly increased wall insulation levels and reduced wall air leakage targets for light-frame wood walls, relative to the 2006 and 2009 IECC. The long-term moisture performance of these new wall systems is not well understood with regard to vapor drive, condensation risk, and drying capability. With moisture performance increasingly becoming a design consideration in the selection of wall systems, home builders and designers need practical guidance for construction of walls that ensure durability of residential buildings.

As part of a broad multi-year research program on the moisture performance of residential wall systems, this project focuses on characterization of energy efficient walls in a sample of new, occupied homes recently constructed around the country in moist or marine climate zones. The data also provides the range of indoor relative humidity levels measured during the monitoring period. The wall system designs and target house air infiltration rates were selected to meet or exceed minimum performance levels outlined in the 2012/2015 IECC, EPA ENERGY STAR Version 3 program, and DOE Zero Energy Ready Home program (formerly Challenge Home program).

The objectives of this ongoing research are to document seasonal wall cavity moisture characteristics, wood structural panel sheathing moisture characteristics, and indoor relative humidity levels in occupied homes. The study scope extends across various climate zones where the wall construction is designed to substantially increase thermal performance and whole-house air sealing achieves much lower infiltration rates.

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