BUILDERS ARE CONSISTENTLY seeking better protection from the effects of windblown rain and other forms of water intrusion. Fortunately, numerous new sill pan flashing products have entered the market in recent years, ushering in new hope for a more moisture-resistant building envelope. The NAHB Research Center and Williams Building Diagnostics, on behalf of the Partnership for Advancing Technology in Housing, have tested a number of sill pan materials, analyzing their effectiveness and the ways they can be implemented to reduce water intrusion in homes (see “Spring Showers,” April, page 82).

Initial testing for the project began in fall 2004 and included field and laboratory evaluations of sheet membrane and preformed pan flashing systems. Each test installation was subjected to a full range of natural weathering tests to determine the nature and extent of any water intrusion that occurred. Analytic processes included thermal imaging, nonintrusive moisture surveys, and the use of post-installation moisture sensors.

To determine the cause of intrusion, engineers evaluated each type of leakage that occurred at the window/wall interface. Field results revealed that when exposed to natural weathering, sill pan flashing was very successful in preventing infiltration in single-family and light-frame commercial applications. In some cases, however, ridges in the sheet membrane material could act as pathways for moisture—an issue effectively addressed by layering the product and by proper sloping of the sill pan.

The final report detailing field results and best practices to improve the effectiveness of the building envelope at the window/wall interface is available this month. Findings include a matrix of available pan flashing and sill protection products that may offer improved performance, ease of installation, and reduced labor costs compared with field-constructed metal pans.

For more information and the full report, visit the Tool-Base Services Web site at