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Your windows are an important design feature of your home not just because of where they are on your wall or because of what view they provide of the outdoors, but also thanks to the casing that surrounds it. If you ever want to replace or install new casing on your windows, take a look at this list of instructions!

Remove the Old Casing

Begin by removing the old casing. With a utility knife, cut small grooves around the edge of the window casing, then take a crowbar and pry it off. Be careful not to damage the actual wall as you do so!

Measuring and Cutting the Trim

After removing the casing, cut a piece of pre-milled sill trim that is long enough to span the full length of the bottom of the window and the length of both vertical pieces of trim on either side of the window; you’ll also want to include ½ inch for an overhang.

Next is the vertical trim. Measure along the inside edge of the window from the the sill to the top and add 3-½ inches to permit a 45-degree angle. Mark these two measurements on the vertical pieces of trim and use a miter saw to cut a 45-degree angle between them.

Before you can measure the last piece of trim, which will go at the top of the window, you’ll need to hang the vertical pieces. Since you may need to adjust them slightly, lightly tap in a few nails at the bottom to hold the vertical pieces in place, and then measure the gap between them for the dimensions of the top piece of molding. Remember to cut its edges at a 45-degree angle so that it fits between the two vertical pieces.

Install the New Casing

Starting from one side and working your way over, nail the top piece of molding into place. Once you install the top, adjust the vertical pieces as necessary so that they fit neatly in the 45-degree angle of the top molding. Once the top and both edges are installed, cut the molding that will go beneath the window sill: It should be the length of the sill but minus ½ inch (¼ inch on each side) to allow for an overhang. Once again, cut this piece at a 45-degree angle.

As a second-to-last step, you can make the returns for the bottom of the window by cutting two small pieces that are the thickness of the molding and cut a scarf joint on one side. Then, center the bottom piece of molding beneath the sill, nail it in place, and then nail the returns in on either side.

Lastly, fill in any gaps or nail holes before sanding, priming, and painting your new window casing!

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