Volume 5, Issue 7 (July 2008)
Design Responsibility for Weathertight Perimeter Detailing for Non-Flanged Windows: Current Practices, Common Problems, and Possible Solutions
Architects typically design details for conditions around the perimeter of window openings prior to the final selection of the actual windows used in the building. This requires the architect to make reasonable, general details regarding the attachment of the window frames, the position of the windows in the wall cross-section, and the weathertight details around the perimeters of the windows. Often, once the final selection of the windows has been made, these general details no longer apply or are not sufficiently detailed to clearly reflect the design intent. In some instances, the details for the windows are intentionally shown in a general, approximate fashion, with the assumption that the actual details will be “designed” during the shop drawing phase. However, the shop drawings typically do not accurately reflect all of the conditions surrounding the windows, and the window installation subcontractor understandably does not want the liability of showing or designing all of these details which they will not build and for which they have no responsibility. Further, while the window shop drawings are reviewed by the architect, the purpose of the architect’s “approval” of the shop drawings is limited. Additionally, shop drawings are not part of the contract documents and, therefore, not part of the design. This results in a common situation where there is no clear basis of design for the weathertightness detailing around the windows. Unfortunately, at present, the authors believe this situation represents the state of the design practice in the building industry. This paper explores common, current practices for designing perimeter weathertightness details for non-flanged windows in commercial applications and how these practices influence the potential for performance problems and water leakage. Suggestions are provided for improvements and alternative methods in design practices. While the paper generally discusses window openings, similar conditions occur at doors.