An analysis of residential window waterproofing systems

Abstract

The prevalence of vinyl nail-on windows in the North American new home construction market has prompted ASTM International to write ASTM E2112-01 "Standard Practice for Installation of Exterior Windows, Doors and Skylights". This thesis focuses on the window jamb flashing recommendation in ASTM E2112-01 for vinyl nail-on windows by asking the question of whether a vinyl window's integral nail-on flange is by itself an adequate jamb flashing. To answer this question, the Jamb Drip Test was designed and completed on fourteen (14) window/wall details. The answer to the question depends on the window/wall construction sequence. When the weather resistant barrier (WRB) is installed prior to the window, it isn't. When the WRB is installed after the window, the nail-on fin is by itself an adequate jamb flashing. Based on this Jamb Drip Test study, a recommended window/wall construction sequence of sheathing- flashing (sill, jamb and head) - vinyl nail-on window - WRB - siding option is proposed. This sequence recognizes that while the nail-on fin may be an adequate jamb flashing, without flashing, the designer cannot take full advantage of the symbiotic relationship between the nail-on flange and the space it creates between the adjoining building elements (e.g. sheathing and the WRB). In this capacity, jamb flashing is added to the construction sequence to protect the sheathing from wetting and aid in directing incidental water to the exterior. Based on this proposed construction sequence, effort was focused on improving the present state of the art window/wall weatherproofing detail. An alternative to the use of high performance sealant to create the seal between the flashing and the window's nail-on flange is proposed. The present recommendation uses a

(cont.) one-piece folded sheet that envelops the window flange, WRB and at the same time incorporates the window flashing function. This novel, dual function (window seal + window flashing system) product is called w-Flashing. The thesis ends with a description of w-Flashing's performance attributes, prototype design and recommended installation sequence around a vinyl nail-on window.