Water intrusion around windows is the movement of water into the wall cavity through rough openings around windows.
Window openings are especially vulnerable areas, because they interrupt the continuity of the drainage plane. To help prevent water intrusion, window openings have to be properly flashed and sealed. Flashing, integrated with the drainage plane, is the key to draining water around openings. Using proper flashing and layering techniques can help combat water intrusion.
To keep water from seeping behind window flashing, the pieces of flashing have to be layered correctly. The sill pan is installed before the window is put in, because it's difficult to flash the sill properly once the window is there. The jamb flashing is layered over the sill pan and extended down past it. The head flashing is installed last, layering over the jamb flashing. In other words, window flashing should be layered shingle style to guide water downward.
Cause 1:
Lack of sill pan flashing
The sill is the most likely place for leaks to occur through a window opening. Wind can drive rain up into the opening at the sill. If the sill is flat or, even worse, sloped toward the interior, wind-driven rain is more likely to enter the opening. Sill pan flashing is essential to eliminating water intrusion through a window.
ProTip!Ensure that the end dam on the sill pan isn't cracked or broken.
Solution
Install sill pan flashing as part of the water management strategy at windows. It provides continuous protection around the sill area and can easily be integrated into the drainage plane using proper flashing techniques. The sill pan should have an end dam that provides additional protection if water finds its way to the back of the sill. If necessary, shims can be placed under the sill pan to create a proper slope for water to drain away.
Cause 2:
Reliance on caulk
While caulking around windows is important, you can't rely on caulks to prevent water intrusion. The primary purpose of caulking is to stop air, not water, intrusion. Caulks deteriorate over time with exposure to the elements and are dependent on the homeowner for maintenance.
Solution
Don't rely on caulking around windows to protect the home. Make sure the flashing, integrated properly with the housewrap, can guide water around the opening and prevent water intrusion. Make sure caulk is only applied behind the nailing fin at the head and jambs. Avoid caulking the sill, so water can drain freely down and out from the home.
Cause 3:
Improper selection of flashing
If inappropriate window flashing is chosen, it can lead to long-term durability problems. If construction tape is used in place of flashing tape, it will be harder to achieve long-term adhesion and overlap to avoid water intrusion. Construction tape is meant to aid in reducing air infiltration, not water intrusion; it shouldn't be used to stop water leaks.
Solution
Flashing tape should be used to seal the jambs and heads of all windows. Inspect all flashing before installing the exterior finish to ensure that proper flashing strategies have been used.
Cause 4:
Improper layering of jamb flashing with head flashing
If the jamb flashing and head flashing of a window are reverse-layered, they will direct water toward the interior of the home. All flashing should be integrated shingle style with the housewrap.
Solution
Begin by installing the jamb flashing over the window flange and extending it 2" vertically beyond the window frame. Then, apply the head flashing so it extends 1" past the edge of the jamb flashing. Layer the housewrap over the head flashing to maintain a continuous path for water to drain.
