How to Build a Window Frame

How to Build a Window Frame

Follow along to learn how to build a window frame. This frame can be used to hold a sash or the frame can hold the glass itself. These steps will outline how to fit the frame itself with glass.

1. Measure the Rough Opening

   To determine the dimensions of your window frame, you must first measure the width and height of the rough opening.

2. Cut Frame Boards to Length

   Cut the two vertical and two horizontal frame boards to the dimensions of the rough opening minus 3/4 inch. This ensures the frame fits in the rough opening with enough room for adjustment.

3. Cut Frame Boards to Width

   Use a table saw to rip the boards to match the depth of the rough opening. This will be the distance between the outermost edge of the interior and exterior walls.

4. Cut a Rabbet for Glass

   On one edge of each board, cut a 1/2-inch-deep by 3/4-inch-wide rabbet (recess in the wood). To do this, set your router table up with a straight cut bit set to 1/2-inch depth. Make multiple passes, adjusting your fence as you go, until the rabbet reaches a width of 3/4 inch.
   

   If you plan to install a sash within the window frame, skip this step.

   Tip

   If you don't have a router or router table, you can skip this step and instead nail down strips of wood around the interior of the frame for the glass to butt up against.

5. Cut Miters

   Set your miter saw to a 45-degree angle and carefully cut each frame board to a 45-degree outside angle, making sure to not remove any of the board's overall length. Once cut, each board will resemble an isosceles trapezoid.

6. Sand to Smooth

   Lightly sand each board just enough to remove splinters and saw marks, but not enough to drastically alter the shape of the wood. This will improve the fitment of the joints.

7. Mockup and Tape

   • Lay the boards on alternating sides with the rabbets facing down and fit each corner together.
   • Tape the boards together at each joint using a strip of painter's tape, then flip the boards over.
   • Ensure the joints fit together tightly in the shape of the window frame and the tape is correctly placed. Adjust if needed.

8. Glue and Clamp

   • Once you're satisfied with the fitment of the joints, loosen the tape, apply an even layer of wood glue to each side of the joints, and fold the boards back together.
   • Firmly reapply the strip of tape on the joint, then clamp the frame tightly together to seat the joints as the glue dries.
   • Wipe away any excess glue.

9. Nail Joints (Optional)

   While the glue is still wet, you can nail each joint to add additional strength. The best way to do this is with a 16-gauge nail gun, however, it can also be done with a hammer and finish nails.

   To do so, pre-drill each nail hole with a bit slightly smaller than the finish nail, then carefully drive the nail into the wood. Drive the nails through each board into the adjacent board, with one nail at the end of each board.

10. Remove Clamps and Sand

    • Once the glue is completely dry, remove the clamps and tape.
    • Sand the entire surface until it's smooth and any residual glue is removed.

11. Buy Glass

    A glass company or hardware store will be able to cut a piece of glass to the dimensions of your frame. Be sure to provide dimensions that are 1/4-inch shorter than the true interior dimensions of your window frame. If you cut a rabbet, be sure to measure from the widest points.

    Tip

    If you are looking for something shatterproof for a playhouse or shed, ask for acrylic or plexiglass instead of glass.

12. Install Glass

    • With the frame laying flat on a work surface, use a stiff putty knife to install an even layer of window glazing against the 1/2-inch wall of the rabbet. Aim for the glazing layer to be around 1/8-inch thick.
    • Place the pane of glass into the rabbet and carefully press it into the glazing until the glazing begins to squeeze out around the edges.

13. Install Remaining Glazing

    • To hold the glass in place, install a thick layer of glazing on the opposite side of the glass. To do this, use a putty knife to press the glazing against the glass at an angle.
    • Once the glazing is in place, begin shaping a clean angle around the entire perimeter. This will help the window shed water and improve its appearance.
    • Wait at least two weeks for the glaze to harden before painting the window frame.

    Warning

    Applying pressure to the glass can break it. Always wear work gloves and eye protection while installing glass.

14. Paint Window Frame

    • Seal all joints with window and door caulk and let dry.
    • Paint all surfaces, including the glazing with a high-quality primer for raw wood, then follow with exterior paint.

How to Install Faux Muntins

You likely know what muntins are, even if you aren't familiar with the term. Muntins are the dividers between the panes that give certain windows that classic style reminiscent of a French door. To give your single-paned window the look of muntins, simply cut 3/4-inch by 1/4-inch flat molding to the height of the window and secure it vertically in the middle of the glass using double-sided mounting tape. Once attached, add horizontal muntins on each side of the vertical muntin.

How to Maintain Your Window Frame

To ensure your window frame lasts for years to come, regularly wax the surface or re-coat it with exterior paint. When necessary, reapply caulk to seal the joints and remove and reinstall glazing as needed.