The window industry has ratings for air leakage through window assemblies. These tests exclude air leakage from the joint between window and wall assemblies or from the sides of the windows. Such leakage is discounted by present window testing standards and labeled “extraneous air leakage.” Air leakage to the window perimeter can significantly effect the overall performance of the window/wall assembly.
A test methodology is presented for quantifying the portion of air leakage that is not measured by current industry standards, but that nonetheless is real and significant air leakage through some types of installed window assemblies.
Design guidelines are proposed to minimize air leakage through the window frame and around the window perimeter. This requires careful selection and detailing of the window and wall system to insure that the air barrier effectively seals to the window frame. These details must be carefully coordinated with the design of the flashing and cavity water-proofing, which have distinct and sometimes conflicting purposes. In three examples, the proper location for air barriers in different types of wall construction is identified along with methods to seal the air barreir to the window.