Window Trim Basics

Replacing window trim updates your decor.

Damaged, cracked, broken or old window trim makes a room look shabby and dated, even if the rest of the room is in tip-top shape. It also can decrease the energy efficiency of your room by allowing hot or cold air to seep through the cracks. Replacing the trim around your windows will update the look of your room and may help decrease energy costs. Replacing them yourself can save a bundle on contractor costs.

Things You'll Need

• Window casing trim
• Window stool
• 2 corner blocks
• Compass
• Tape measure
• Table saw
• Jigsaw
• Hammer
• 18-gauge nails
• Nail set
• Construction adhesive

Instructions

1. Mark the window jambs for the reveal, which is the distance that the casing trim will be set back from the inner edge of the jambs. Open the compass to 1/4-inch. Use the jamb as a guide to scribe a reveal line on both side jambs and the top jamb.

2. Place a piece of window casing against the wall. Line the inner edge up with the reveal line. Make a mark on the wall at the outer edge of the casing trim. Repeat this process for the other side.

3. Cut the window stool to the appropriate length. The window stool is the trim piece on the bottom of the window that creates a small shelf, sometimes referred to as the window ledge. Measure the distance between the two marks and add two inches. Cut the window stool to this measurement.

4. Measure 1 inch from each end of the stool. Place the stool across the window and align the marks on the stool with the marks on the wall. Make a mark on the stool at the inside edge of the jamb on each side. Extend this mark across the top of the stool.

5. Open the compass to the same width as from the sill trim to the front edge of the sill. Hold the stool across the opening and align the pencil marks. Place the point of the compass against the wall and scribe a line on the stool from each edge to the line at the jamb. Cut notches along these lines with a jigsaw.

6. Attach the stool to the sill using 18-gauge nails. Countersink the nails using a nail set.

7. Place one end of the casing on the stool. Line the inside edge up with the reveal line. Mark the casing at the top jamb's reveal line. Cut a square cut on the table saw at this mark. Repeat this process for the other side.

8. Apply a bead of construction adhesive to the back of each piece. Line up the trim with the reveal line. Attach each piece to the wall with 18-gauge nails.

9. Place a piece of casing trim across the top of the window. Mark each end of this piece at the inner edge of the side casing. Make square cuts at each mark. Attach this piece to the wall using the same process as for the side trim.

10. Apply construction adhesive to the back of each corner block. Attach to the wall at each upper corner using 18-gauge nails.

References

• This Old House: How to Trim Out a Window
• Kelleher Corporation: Installing Window and Door Mouldings