Adding window trim is an instant way to bump up the beauty of any room. A miter saw is an essential tool to successfully learn how to install window trim. If drywall is interfering with placing trim against the jambs, you can trim it down with a utility knife. More extensive drywall blockages require removing edges with a hammer. Remove drywall with care so that the drywall will remain intact beyond the outside edge of the trim.
Tips for Success
- Trim largest windows first because scraps might fit on smaller windows.
- Cut directly on your pencil mark for the most accuracy.
- Start on the thickest edge of the trim when cutting.
- Do not nail trim pieces within 2 inches of their ends.
How to Install Window Trim Step by Step
- Use a miter saw to cut a 45-degree angle on a piece of trim.
- Hold the cut piece along the top of the window.
- Position the shorter end of the angled cut so that it’s centered along the edge of the side window jamb.
- Mark the other end of the trim with a pencil where it meets the inside edge of the side jamb.
- Cut a 45-degree angle outward from the pencil mark.
- Hold the top trim piece along the bottom of the top window casing.
- Nail the trim to the jamb with 1-inch brads every 6 inches.
- Nail the trim to the framing with 2-inch brads.
- Select another trim piece and cut a 45-degree angle on it.
- Hold it against the angled edge of the top trim to see if it fits snugly.
- Cut again if you need to make adjustments to achieve a perfect corner.
- Hold the side trim piece in place again and mark it 3/16 of an inch below the bottom of the jamb.
- Cut the bottom angle.
- Spread wood glue on the edge of the top miter.
- Nail side trim to the jamb and frame with 1-inch and 2-inch brads respectively.
- Nail the mitered corner from the top and side edges with 1-inch brads.
- Wipe away excess glue.
- Repeat steps 9 through 16 to trim the other side.
- For the bottom trim, cut a 45-degree angle on a long piece of window trim.
- Fit it against one corner of the side trim.
- If necessary, adjust the cut to ensure a tight fit.
- To mark the second cut, hold the trim tight against one side and mark where to cut the other side.
- Make the final 45-degree cut.
- Spread wood glue on the angled edges of the bottom trim.
- Fit the trim into place and nail to the jamb and frame.
- Nail the mitered corners together from side and bottom edges with 1-inch brads.
- Wipe off any glue that squeezed out of the miters.