How to Trim a Bay Window

Once you've installed a bay window, dress it up with trim. We'll show you how.


Bay windows are dramatic additions to any home. And though they're a little more difficult to install than a standard window, the end result is well worth the effort.

This tutorial shows you how to dress up a bay window with trim. We'll walk you through adding facia to the skirt, installing molding, and placing hardware. Depending on the trim you choose, expect to spend at least a day installing it. This project requires good carpentry skills and one or two strong helpers.

What You Need

  • Facia
  • Table saw, power mitersaw, or circular saw
  • 6d galvanized box nails
  • Hammer
  • Drill
  • Forstner bit
  • Wood plugs
  • Level
  • Carpenter's glue
  • Sandpaper
  • Insulation
  • Casing
  • Tacks
  • Finishing nails
  • Wood putty
  • Finish or paint
  • Paintbrush
  • Screwdriver

Step 1: Add Facia


Add facia to the skirt. Make the angled cuts with a table saw, power mitersaw, or a circular saw. These angles can be difficult; always try the joint before cutting the piece to final length so you can recut the angle if needed. Tack each piece in place using 6d galvanized box nails. Complete the final nailing only when you are satisfied with all the joints.

Step 2: Fasten Jambs and Seat


Complete the fastening of the jambs and seat. For a clean finish, bore countersinks to hide the screw heads. Use a Forstner bit to make a clean hole. Purchase wood plugs for the holes.

Step 3: Check for Level and Plumb


Make a final check for level and plumb all around. Adjust the shims accordingly. Check again that the windows operate smoothly and are aligned with the frames. Fasten the screws in place.

Step 4: Install and Sand Caps


Apply carpenter's glue to the plugs and set them in the fastener holes. Gently tap the caps until they are flush with the surface; most are tapered for this purpose. Once the glue dries, lightly sand the caps.

Step 5: Add Insulation


Stuff insulation into the gaps between the side and top jambs and the house framing. Stuff gently but fill the spaces completely, or use nonexpanding foam insulation.

Step 6: Add Casing to Apron


Tack pieces of casing in place and measure for the length of the apron. Fasten the apron to the seat board with finishing nails. (If your unit has a seat with a finished edge that extends beyond the wall, place the apron under the seat.)

Step 7: Install Casing and Hardware


Install the casing. Fill all the nail holes with wood putty, sand smooth, and apply finish or paint. Install the opener cranks or other hardware and the window screens.

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