Window openings can be vulnerable to water ingress in any wall assembly, whether they’re a traditional wood-frame wall or an ICF system like Element ICF.
Fortunately, the flashing methods that block water ingress through windows in traditional walls apply just as well (with small tweaks) to ICF walls, too.
And in the post below, we will explain how to properly flash a flanged window in an ICF wall in a way that blocks water from making its way through the assembly yet leaving it a proper drainage path outside.
A 7-Step Method for Flashing a Flanged Window in a Element ICF Wall
Flashing a flanged window correctly is not particularly challenging in an ICF wall.
The key factors to remember are to create a proper drainage path at the bottom of the flange, and to overlap the individual flashing elements correctly.
Following are the seven steps for flashing a flanged window in a Element ICF wall opening that has been buck with Element Pro Buck:
1. Install Pan Flashing At the Sill
Job one is to install pan flashing at the window sill. To do so, follow the simple steps below:
A self-adhering or liquid-applied membrane will do, as long as it:
- Extends a minimum of 8 inches up the window jamb, and
- Extends at least 2 inches over the top of the water control layer or 2 inches past the window flange
2. Flash the Window Jamb
Apply a layer of self-adhering or liquid-applied flashing membrane to the full length of the window jamb. You must ensure that the flashing bonds well with the rough opening, so use a roller when applying the membrane to the jamb.
Also, note that the header flashing (discussed below) will have to overlap the jamb flashing.
3. Install the Window
With pan and jamb flashing in place, you are ready to affix the window assembly to the substrate. However, when installing the window, be sure to NOT fasten the bottom flange, and use shims to create a drainage path where the bottom flange is.
To boost the wall’s thermal performance, place the window in line with the exterior insulation panel of the ICF wall (if possible). Of course, be sure to use the Element Pro Buck to support the window and reduce thermal bridging.
4. Apply Membrane at the Jamb
Apply a self-adhering or liquid-applied membrane to the full length of the jamb, extending over the entire flange and onto the ICF panel surface by 2 inches or more.
5. Flash the Header Above the Window
A recommended next step is to apply a metal or vinyl header flashing above the window. This is not commonly done but is a best practices recommendation. Then, apply a layer of self-adhering or liquid applied membrane over the header flashing. This layer will also have to overlap the jamb flashing in its entirety (as discussed in Step 2), and extend over the ICF insulation layer by at least 2 inches.
6. Install Trim Boards and Cladding
Once you’ve completed step 5, the window will be adequately flashed. This means you can move on to fitting the trim boards and cladding at the window opening per the design requirements.
7. Caulk the Window Assembly
Creating an air seal at the window assembly is the last of our seven steps, and it’s done by sealing the window on the interior. Flexible caulking along with a backer rod is the best method for caulking the window assembly to create an effective air seal.
