How to Frame a Trapezoid Window

  • 2-8 hours
  • Intermediate
  • 250-500
What You'll Need
Circular saw
Hammer and nails
Measuring tape

A trapezoid window gives your home a different look and is a cool way to work with slanted roofs. If you want to install or build a trapezoid window, it’s a lot like installing a regular window, but you have to use the measurements of the trapezoid window.

Step 1 - Planning the Trapezoid Window Frame

When you plan the rough frame for your new window, you’ll need to plan an extra 2 inches for each dimension. For a normal window, you only have 4 dimensions, but for a trapezoid window, there will likely be 3 measurements, the taller side, the middle and the shorter side.

Step 2 - Using an Existing Wall or Building a New Wall

If you’re using an existing wall, you’ll want to cut away the drywall to see the studs you’ll be working with. If you’re using a new wall, you’ll build from scratch the proper studs and dimensions.

Step 3 - Cutting Away Studs

Cut away the studs so that your window will fit properly. You’ll need to measure the cut away studs with the angle of the trapezoid window, for example, if you cut away the stud at the middle of the angled side, use the middle trapezoid window angle as a measurement guide. You should leave 3 inches for the king studs and header.

Step 4 - Installing King Studs

King studs are the vertical replacement for the studs you have cut away to install the trapezoid window. Measure from ceiling to floor to know how long your pieces of lumber should be, then use the outer measurements as your guide.

Step 5 - Installing the Header

If the top of your trapezoid window is the edge that has an angle, your header will be installed at the proper angle. Use the studs you cut away as a guide to how the header piece should be installed. Use 2 pieces of wood the width of the window frame and attach them to the studs, side by side. Nail the 2 header pieces to one another.

Step 6 - Installing the Bottom of the Frame

Using your rough frame estimate cut a piece of wood to fit the bottom edge of your window and install it. This is called the sill plate. Attach the sill plate to the king studs on either side. Install 3 cripple studs. A cripple stud goes from the floor to the sill plate. Attach one to either side of the sill plate up against the king stud and one in the middle of the sill plate.

Step 7 - Installing Trimmer Studs

Trimmer studs attach from the header to the sill plate and are attached to the header, sill plate and king studs on either side. Make the appropriate measurements from the header to the sill plate, using your rough frame measurements, then attach the trimmer studs on either side. Now you’re ready to install your window.