Windows
and doors are full penetration items—they go through the entire wall.
This means interior pressures are not really well-buffered to exterior
environments. These through-wall pressures are more significant than a
halfway penetration, such as outlets or water bibbs. The pressure can
vary greatly and are related to the height of the structure, exposure to
wind, and the size and location of the opening. This is referred to as
“design pressure.” Quality fabricated windows are tested and rated for
pressure and then assigned a performance class. Selecting the properly
rated window is critical, as well as ensuring the transition from the
window to the cladding provides a seal against water intrusion. A bad
window leaks, a good window does not.
There
are many types of windows and configurations. There are two basic
categories: flanged and non-flanged. Flanged windows are the most
popular window installed today. They are used in the residential and
light commercial markets. Most are made from PVC and installed with the
flange being the attachment to the sheathing. The metal non-flanged
window is also known as a “storefront” style. Many wood-framed windows
are also a non-flanged style. Regardless of the style or type of window
used, flashing or sealing the perimeter of the window frame to prevent
water intrusion is critical. Success typically relies on following a
recognized industry standard for flashing and coordination between the
trades. Communication is important, as no one trade is typically
responsible for all phases.