Today, the City of Seattle announced the release of a technical study of moisture damage in newer buildings conducted by the Oak Ridge National Laboratories (ORNL). This research endeavor seeks to expand the knowledge base for regional builders, owners, and officials concerned about significant moisture damage encountered in recently built multifamily structures.

The study, which marks the first phase in technical analysis of unusual moisture damage, was requested by members of the Seattle Construction Codes Advisory Board, the Seattle Department of Design, Construction and Land Use, and the Washington State University Cooperative Extension Energy Program.

Study Findings
Researchers at the nationally recognized laboratory have completed computer simulations of the hygrothermal performance of 35 wood-frame exterior wall systems used in the Seattle area. Among their findings:

• confirmation that insulation requirements have a marginal effect on wall performance;
• the importance of controlling interior relative humidity below 60 percent for most of the year; and
• the importance of selecting building materials that allow walls to dry to both the interior and the exterior, provided interior conditions allow drying to the inside.

In addition, members of the local advisory board agreed on the necessity of incorporating moisture control fully into the design of the building, providing detailed installation instructions for construction crews, and ensuring effective coordination at the jobsite of subcontracted work.

The computer model used by the ORNL researchers predicted the performance of each wall system on an hourly basis over a two-year period, taking into account the cumulative effects of interior and exterior environments, leaks, and the hygrothermal performance characteristics of each wall component. Hygrothermal performance measures how building systems transfer heat, air and moisture. The relative performance of each wall was then ranked based on a "mold growth index" developed by building science researchers from VTT Technical Institute in Finland. The study assumed good quality construction.

The simulations mark Phase I of a continuing study, and provide a preliminary assessment of typical walls used in multifamily construction in Seattle. Phase II will develop a database of the properties of construction materials. Phase III will seek ways to improve water management capabilities of wall systems through both field work and computer modeling. Phase I of the study is available from DCLU both online and in hard copy (see box above).