Guiding Principles of Fenestration
by Jim D. Katsaros
Because of the complexities involved in the installation of the many different types of fenestration products in all the possible wall systems and expected environmental exposures, it is impossible to attain prescriptive installation details that cover all of the potential installation configurations. Here are some guiding principals for
Maintain continuity between flashing and the window-wall
Ensure correct shingling/lapping of flashing and other water-resistive membranes and
Provide a drainage path for leaks;
Ensure installation conditions that promote adhesion of sealants and flashing; and
Use materials that have adequate durability for the anticipated
There are also six areas that require assessment in any
The continuity between the fenestration product and the water-resistant barrier is best provided by the flashing products, and self-adhering flashing products provide the greatest water-resistant seal over this interface if used properly. Lack of continuity at this interface is a source for leaks causing air and moisture
2) Correct Shingling/Lapping of Materials
Shingling errors can occur when the flashing at the head of the window is installed under the flange of the window or where the head flashing is applied over the water-resistant barrier (WRB), rather than the WRB lapped over the flashing as well as the sill flashing applied over the sill flange. In both of these cases, water that gets behind the WRB and/or the flashing is likely to travel behind the head of the window and enter into the wall cavity or building’s interior.
3) Provide a Drainage Path for Leaks
The original ASTM E2112-01 guideline for the installation of doors, windows and skylights detailed an installation method, where the sealant was applied around the entire perimeter of the integral flange of the fenestration product to create a full barrier at the external interface between the window and the wall system. The shortcoming with this method was that, if any leakage occurs, then the water leakage into a barrier installation system will be trapped in the wall cavity or directed to the interior.
The drainage system enables the installation to manage this water intrusion. This is accomplished by leaving openings in the seal between the window flange and the sill pan flashing at the sill of the window. In this drainage system, a robust air and water seal at the interior perimeter joint between the fenestration product and the wall cavity is essential. This seal must be able to withstand any pressures imparted through the ‘open’ sill at the exterior interface.
4) Installation Conditions that Promote Adhesion
The degree of moisture, surface contamination and substrate surface continuity all have significant impact on the ability for the flashing and sealants to adequately bond and provide a moisture barrier. It is critical that these conditions are considered to achieve a successful installation and that the installer involves the flashing manufacturer to ensure the right products are used.
5) Material Durability
Whereas the previous principle is concerned with the initial conditions for installation, it is equally important that the materials used to seal the fenestration interface with the wall perform in the field as required over the life of the installation. It is essential that the installer and manufacturer ensure that materials used for the installations can withstand the end use
6) Risk Assessment
The decision as to what installation method to use is actually an assessment of risk tolerance, bringing together a number of risk factors, which include water-resistance rating of the fenestration product, moisture tolerance of the assembly, exposure to the environment, local rainfall amount, drying potential and workmanship. All these factors need to be taken into account when determining the installation practice to be utilized.
Jim D. Katsaros, Ph.D. is the flashing systems development leader for DuPont, and is the chairman of the Installation Committee for the Fenestration Manufacturers Association. Mr. Katsaros’ opinions are solely his own and not necessarily those of this magazine.
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