How to Trim Interior Windows

Jane and Sonja

Outlining the step by step instructions (with photos) on how to trim interior windows.

5 from 2 votes

Using a utility knife, trim away any excess spray foam that's expanded on to the window sill.
Determine the length, width and depth you will need for the jambs to cover the exposed 2x4 frame.
Insert the bottom jamb into the sill and level the jamb with shims.
Repeat with the side jambs and then lastly with the top jamb.
Nail the jambs in place.
Measure the bottom width of the window from jamb edge to jamb edge. Add 1/8" on either side for the reveal.
Cut the window casing using a mitre saw at 45 degree angle on both ends.
Line up the window casing over the bottom jamb to reveal ⅛” (along the top and sides of the casing). Use the level to ensure the casing is straight.
Using the wood glue, glue the casing to the wall and nail the casing with the nail gun.
Repeat the process for the top and vertical sides of the window.
Once the casing has been installed, take the wood filler and fill in the nail holes and mitered corners. Let the wood filler dry.
Once the wood filler is dry, use a fine gauge sandpaper to smooth where the holes were filled.
Lastly, paint or stain the trim to finish.

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