How to Frame Wooden Window Trim

What You'll Need
Miter Saw
Finishing Nails
Measuring tape
Window trim

When you are installing a new window, remember that you will also need to install window trim. In addition to functionality, an aesthetic charm is given to a window by the type of trim surrounding the window. Once you have determined that you will be installing your own window trim, your next task will be to determine the proper way to frame that window trim. Framing anything is a very precise art, and careful time and precision will be needed in order to complete the job successfully.   

Step 1: Measuring Window

For any job involving careful precision, measuring the window frame itself will be extremely important to your finished results. To do this, measure each side of the window as well as the top and bottom to within an eighth of an inch (1/8”). Adding 1/4" to each measurement will allow you to create a visually interesting reveal of 1/8" on each side when you install each section of trim.

Step 2: Cut Window Trim

Use a miter saw to cut the end of a length of the window trim you have selected at a 45 degree angle. Then, measure from the shorter edge of the angle you just created, measure the distance of one edge of the window frame that you already measured and make a mark. Using that mark as the short end of your next cut, use your miter saw to make another 45 degree angle. Repeat this process until you have 4 sections of window trim cut with 45 degree angles on each end. These should then fit together to form the 4 corners of your frame. 

Step 3: Install the Window Trim

Hold each piece of window trim in place along the window frame in order to make sure that you properly measured the reveal on each piece. If these pieces were measured improperly, you will need to cut new ones, so it is extremely important to measure and cut precisely the first time. Once you are satisfied that your measurements were correct, level the bottom piece of trim along the bottom edge of the window frame and then attach it to the frame with finishing nails. A mild adhesive may be used to hold the trim in place while you attach it more permanently with nails.

Connect one of the side pieces to this bottom piece at the miter joint you have already pre-cut and secure it to the frame with finishing nails in the same fashion. Using this same technique, attach the other two sections of trim to the window frame and attach them with finishing nails. 

Once you are completely satisfied with the placement of each trim and the joints at each end, drive through nails every 8 to 10 inches along each piece of trim in order to permanently secure them to the frame.