Installing Flanged Windows – Part 3: Install the Window

If you're replacing windows, this covers what happens once a window actually goes into the wall opening, and it explains why some small details matter for how long the window lasts. The builder in the video installs a window with a flange (a strip around the frame that gets nailed or screwed to the wall and sealed), and stresses a few things worth knowing if you're hiring someone for this work. First, metal clips that bolt the window frame to the framing add real structural holding power, so the window doesn't rely only on the flange to stay put during storms or high wind. Second, the shims used to level the window in the opening matter: composite shims (rather than wood ones like cedar) don't soak up water and wick it into the window frame or trim, which can cause hidden rot or paint damage over time even if the window itself is sealed correctly.

The other detail is drainage. The installer leaves the bottom edge of the window unsealed and uses small "horseshoe" shims underneath it, so that if water ever gets past the window seal — from a storm, a bird strike, or just years of sun exposure — it has a path to drain back outside instead of pooling and causing damage. None of this is something you'd inspect yourself, but knowing these terms (window clips, composite shims, drainage shims) can help you ask better questions if you're getting new windows installed and want assurance the job accounts for long-term water and air performance, not just appearance.