By Tyler Grace
The consequences of a failed window installation
No matter how well a window is made, it will not perform properly if it is not installed properly. I recently encountered some poorly installed windows on a remodel project. The exterior was traditional stucco, so at first glance we had no idea the extent of the damage. Once we started to remove the layers, we uncovered a slew of mistakes. There were no head flashings, the flanges were not back-caulked, there was no drainage plane behind the stucco, they had taped the bottom flanges of the windows, they had not integrated their sill pan flashing into their weather resistive barrier (WRB), layering of tapes and WRB’s were incorrect, and they caulked any sign of a leaking after the fact which only exacerbated the issue. Let’s dig into why these mistakes were so costly and go over some keys to proper installation.
Head flashing
A head flashing is used to divert water away from the head jamb or head trim on a window. This is an extremely important detail because when water runs down the exterior of a building, the head jamb or trim above the head jamb takes the heaviest beating. If the bulk of the water is not diverted away from this area, even with adequate flashing and waterproofing at the window flange, water may infiltrate. These flashings can be made of rigid metal or vinyl. They must be properly integrated into your flashing tapes and WRB in order to work properly.
Back caulking
Not everyone back- caulks window flanges, but for me it is an additional line of protection. Adding sealant behind the flange serves as the secondary line of defense for water and is a prescribed step in Andersen’s installation guidelines. The primary seal in a flanged window installation is the flashing tape over the flange. If water migrates through any/all of your other layers, the sealant behind the window flange can serve as a last line of defense against water and air. I apply the sealant on the top and sides of the opening, but it is critical to not apply the sealant to the bottom flange if you want water to be able to drain out of that area. No matter what we do, water will at some point infiltrate our openings, and we must ensure it has a place to escape.
Drainage plane
These days, many exterior finishes require the use of an exterior drainage plane, mat, or system behind them. We are building our homes tighter than ever, and we must make sure water has a place to weep out from behind our facade. I view siding and exterior finishes similar to tile; it is not waterproof and is not intended to be. It is there for aesthetic purposes, and all that lies beneath the finish must not only be air and watertight, it must also allow for drainage. This is the purpose of these drainage planes — to shed the water that gets behind our exterior finish and not trap it.
