How to Repair Interior Window Trim Around Window Frames

A window window with thick trim in an empty room.
What You'll Need
Pry bar or screwdriver
Tape measure
Window trim material
Measuring square
Circular saw
File or cir-form
Nails or glue
Protective finish

While interior window trim might not be as susceptible to damage as exterior trim, it is still important to keep it in good condition. Over time the trim will start to deteriorate no matter what you do, and this means you need to find out how to repair and replace it. Since a good trim can prevent air from escaping through gaps in the window frame, repairing it will make your home much warmer and lower the amount you have to pay in heating bills. With the right tools and materials available you should be able to remedy this problem easily and quickly. As always, proper preparation will ensure that the project is as easy as possible.

Step 1 - Remove the Old Trim

Before you can start installing new window trim, you need to remove the old. This is normally nailed or glued in place depending on the materials used, and then it will be filled on the inside using caulking. First, use a knife to scrape out and cut away the caulk between the frame and the trim. Use a small pry bar or a screwdriver to then lift the window trim off, starting at one of the edges.

Try to keep the window trim in one piece so that you can use it as a template to cut the new pieces. If there are any nails left in the window frame, you will need to use pliers or a hammer to pull them out.

Step 2 - Measure

Now you will need to measure the size of the window so that you can cut your trim to the right size. Use a tape measure to find the inside dimensions of the window frame. If you managed to keep the existing trim intact, you will be able to skip this step.

Step 3 - Prepare the Window Trim

Use a pencil to mark the required length for the project on the material you're using; remember that you will need four pieces per window. The width of this trim will be up to you. If you need it to fit over a space equivalent to the old one, make sure your measurements match up accordingly. Then, get mitered corners by marking a 45-degree angle at the top of the length, starting at one edge and extending it past the total width of your trim.

If you saved the old pieces of window trim, you will be able to lie these on top of the new lengths of material and outline them with a pencil.

Step 4 - Cut the Window Trim

The window trim can be cut very easily by using a regular circular saw. If there are any rough edges you can use a file to remove them.

Step 5 - Fix the New Window Trim

The new pieces of window trim need to be fixed to the window frame next. Use nails or glue according to your own preference.

Step 6 - Finishing Touches

There will probably be gaps between the window trim and the window frame that need to be filled with caulking. Dip your index finger in water and use it to smooth down the bead after you've applied it to improve the look.

You can also add paint, stain, or varnish for a professional-looking, protective finish on your material, depending on what it is.