Volume 39, Issue 2 (March 2011)
Investigation of the Condensation Potential Between Wood Windows and Sill Pans in a Warm, Humid Climate
As building envelope designers have become more attuned to the need to prevent moisture intrusion, window flashing has become more of an issue. Sill pans are an important component of many window flashing systems. These pans are constructed from a variety of materials, including metal, and are located beneath the window sill. Sill pans are also typically formed to have back dams and end dams so that they can redirect water that leaks through the window to the exterior. Draining the water to the outside requires a vented area between the sill pan and the window sill, and there is speculation that environmental humidity can condense within this space in warm, humid climates. This condition may be most severe when the sill pans are made from materials with high thermal conductivities, like metal. If water were to condense in this cavity, condensate may periodically contact the exposed underside of a window sill, which, if wooden, may cause decay. In order to determine if condensation-related moisture could negatively impact the performance of a window, a wood window was installed with a metal sill pan at the Oak Ridge National Laboratory’s Natural Exposure Testing Facility near Charleston, SC, to measure parameters including temperature, humidity, and wood moisture content. Based on the testing results, recommendations are made to maximize moisture performance of wood windows installed with sill pans in warm, humid climates.