How to Build a Window Trim

As part of this bathroom remodel, we wanted to update the window trim to something more of a focal point. aesthetically pleasing and with a window sill. This simple change made the window a special addition to the bathroom. I also love having the window sill, it’s the perfect spot for my little watering can, a candle, plant or little Christmas trees this time of year. Follow along to find out how to build a window trim.

You can read about this whole bathroom remodel including the reveal here.

(This post contains affiliate links. This means I receive a small compensation at no cost to you. For example, as an Amazon Associate I earn from qualifying purchases. You can read more about it here. Thank you for your support!)

Materials Needed:

wood planks (We used a mixture of pine and poplar.)

trim screws

clamps

miter saw

drill and impact driver

sandpaper (180 grit)

wood filler

level or laser level

primer, paint and brushes

How Do I Build a Window Trim?

Step 1

Remove the original window trim and measure the opening.

The window after the old trim was removed.

Step 2

Decide on the general look you want to achieve. Once you have this in mind and your measurements, you can purchase and cut your wood to size.

Step 3

Cut the wood to size using the miter saw.

Step 4

When you make a window trim, start with these four pieces and attach them together.

The above photo shows the starting pieces. You will not be building it onto the wall. You will build it altogether first, then you will install it to the wall. Start by attaching the the first four pieces that will be surrounding the window. Attach the side pieces to the top and bottom pieces using the trim screws and the impact driver. You will need around 8 screws.

Step 5

For reference, here are the measurements of what we used.

The measurements of the window trim pieces

Now that you have the basic frame, next you will add the extended pieces. Line up the pieces the way you like them, then hold them in place using the clamps. Next, connect them together the same way as before using the screws and impact driver. Go in deep enough with the screws to be able to fill in the holes next with wood putty. Sand down any rough edges.

How to build a window trim, clamp the pieces together before screwing them together.

How to build a window trim. screw them together with trim screws.

Step 6

Now your frame is built and ready to install. You will be attaching it to the stud wood framing around the window. You can clamp it in place as he did to the open window, or have someone hold it up into place. Use a level to make sure it’s just right (Tim used a laser level which was helpful, but a regular level is fine). Screw it into place using the trim screws all around until it feels secure. Use wood putty to fill in the holes.