How to Install Interior Window Trim | Ask This Old House

Ask This Old House general contractor Tom Silva helps a homeowner trim a window to match the rest of the house.
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Time: 3-4 hours
Cost: $100
Skill Level: Moderate
Tools List for Installing Window Trim:
Prybar
Hammer
Table Saw
Miter Saw
Compass
Hand Plane
Sandpaper
Speed Square
Nail Gun
Shopping List:
Window Stool Molding
Extension Jamb Molding
Window Casing
Window Apron Molding
Shims
Wood Glue
Minimally expanding foam insulation
Steps:
1. Remove any existing casing, stool, or apron molding.
2. Use the table saw and miter saw to cut a piece of stool molding to fit between the windows. Leave the ends long.
3. To determine the finished length of the stool, hold the extension jamb and casing in place, leaving a _” reveal between them. Then set the distance from the face of the casing to the face of the stool and transfer that measurement from the side of the casing to the stool.
4. Ease the edges of the stool with a block plane and sandpaper.
5. Use shims to make the stool square to the window.
6. Use the nail gun to nail the stool in place.
7. Rip the extension jamb pieces to the correct width, then cut them to length.
8. Cut the casing to length, mitering the corners at 45 degrees.
9. Make a mark _” from the edge of the extension jamb where the casing will sit.
10. Assemble the extension jambs and window casings as a single unit on a workbench or sawhorses using screws, wood glue, and nails.
11. Dry fit the trim assembly in the window opening. Shims may need to be added or the plaster may need to be taken down slightly.
12. Use minimally expanding foam in any joints around the window and around the extension jambs.
13. Nail the trim assembly in place.
14. Attach the window stool to the casing with a screw.
15. Cut the apron to the correct length, which is the distance from the outside of the casing to the outside of the casing.
16. Glue and nail the apron in place.
Resources:
Tom installed 3_" Colonial casings and used stock lumber for the remaining pieces.
All of the wood and tools used can be found at a home center.
Special assistance with this project was provided by Cleveland Lumber Co (www.clevelandl....
About Ask This Old House TV:
Homeowners have a virtual truckload of questions for us on smaller projects, and we're ready to answer. Ask This Old House solves the steady stream of home improvement problems faced by our viewers-and we make house calls! Ask This Old House features some familiar faces from This Old House, including Kevin O'Connor, general contractor Tom Silva, plumbing and heating expert Richard Trethewey, and landscape contractor Roger Cook.
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How to Install Interior Window Trim | Ask This Old House
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