Selectwood Perspectives

FALL 2019

"WINDOW FLASHING 101

One of the most important pieces to the puzzle when installing modern day windows is how to manage water. Any new window is expected to seal out wind and water from between the sash and the frame, but how does one ensure keeping water out of the rest of the rough opening? Let’s talk about a few key elements in using the most up-to-date and effective types of flashing; adhesive-backed flashing tape.

There are several types of flashing tapes available, with the majority being produced with three types of adhesive: asphalt, butyl or acrylic, as well as some hybrids. Most window manufactures recommend the use of butyl-base or acrylic-based adhesives. Almost all window manufacturers recommend not using asphalt based adhesive. The chemicals in asphalt adhesives can cause window flanges to deteriorate over time. Always follow the Manufactures recommendation when choosing the flashing tape.

Taking the proper time to install a window can seem labor-intense and expensive, but a necessity to keep moisture out. This added time and expense if far less than the cost of call backs when water is found leaking in through an improperly installed or flashed window.

Installing the Window – Let’s assume the building paper has been properly cut back to expose the window opening. Prior to putting the window unit into a rough opening, steps need to be addressed to make sure sills are flat and level and a sill pan is covering the base of the RO and turned up the sides. The next step is to place a bead of sealant to the jambs and head of the window opening making sure not to put sealant on the sill (meant to allow moisture to escape out through the sill opening). Place the window into the opening, check for plumb and level and install fasteners to Manufactures specifications.

Once ready for flashing, the first step with the tape is to line up one side of the exterior frame, and cut the tape to length to roughly the width of the tape (usually 3”-6”) longer on the bottom and at the header. So, if you have 4” flashing tape, cut your jamb piece about 6”-8” longer to go past the head and sill. Another very important step is to make sure the tape is fully covering the nail flange, rolling the tape up onto the edge of the frame about ¼”. The tape should extend out over the nail flange and onto the weather barrier. Follow the same instruction for the opposite jamb.

Installing the flashing tape to the head or top of the window:
The flashing tape should extend past the jamb flashing tape by approximately 1”. Ensure the flashing tape adheres to the edge of the window by a ¼” and extends over the nail flange and onto the sheathing. Now that all three sections have been installed, use a wheeled roller to press the flashing tapes securely onto the nail flange and weather barrier. Bring the top weather barrier down over the head flashing tape and secure the seams with tape.

This is a brief explanation of a basic window flashing detail. Following Building Code and the Manufactures recommended practices is of the utmost importance. A properly flashed window should keep water from entering and allow moisture to escape the rough opening through the sill.