How to Straighten a Window

Ask This Old House general contractor Tom Silva shims a window that has fallen out of parallel due to improper installation

Moderate

$20

3-4 hours

Steps for straightening a window:

Use a utility knife to score the window casing from the wall and from the jamb.
Carefully pry the casing away from the wall.
Cut a small amount of the wallboard with the utility knife to see the rough opening.
Place shims in the gap between the window and the rough opening. Repeat this process on the other side of the window until the window becomes parallel again.
Check the window for parallel by measuring the width of the window at the top, middle, and bottom. If the measurements aren’t equal, adjust the shims accordingly.
Nail the window and the shims to the rough opening using a nail gun.
Cut the excess from the shims off with a utility knife.
Fill the gap between the window and the rough opening with spray foam insulation designed for windows and doors.
Reattach the casing with wood glue and the nail gun.

The materials Tom used to fix the window gap, including shims, the hammer, and the utility knife, can be found at home centers.