How to Build Bay Window Cornices

Written by chuck brown
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How to Build Bay Window Cornices
Bay windows allow in great natural light. (bay windows image by L. Shat from

Bay windows offer more of a 360-degree view than regular flat to the wall windows. For this reason, they are popular among architects and homeowners. While their design is popular, decorating them can sometimes pose distinctive problems. These conundrums usually are solved by treating the bay window as three separate windows, usually a large window flanked by two smaller ones. Window cornices offer an attractive fashion solution, and the materials to make them can be found online and at home-decorating stores. Enhance your bay windows and build your own cornices.

Skill level:

Things you need

  • Foam board
  • Utility Knife
  • Glue
  • Floral picks (minus the wires)
  • Straight pins
  • 6-penny nails, 6
  • Hammer
  • Fabric

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  1. 1

    Measure your bay window at the top. Take two measurements, the centre and one side, since both sides are equal. Include any treatment you already have in place in these measurements and add 8 or more inches to the entire measurement to your preference. Add enough for room to mount the cornice on the wall and cover what is already there.

  2. 2

    Measure the foam board material according to the window measurements. Use a utility knife and cut the board into the three needed pieces first. Cut two more end pieces 2 to 4 inches wide. Be sure to use a straight edge to mark and cut the board while holding the material firmly in place.

    How to Build Bay Window Cornices
    Board made from foam material is an excellent lightweight choice for cornices. (pink styrofoam business image by robert mobley from
  3. 3

    Assemble the five pieces, the three top pieces and the two ends. Use floral picks, one every 2 to 3 inches and glue to attach the two end pieces to the two side window pieces first. Cover one end of the floral pick (wire removed) in glue and press it into the cornice piece. Do the same with the other piece to join them. Each side window piece will have one end piece on the end of what will be the entire assembled cornice.

  4. 4

    Attach the bigger centre piece to the two side pieces you just added the end pieces to in the same manner. Be sure to measure and accommodate the angle of the bay window, as you attach the two side pieces to the middle piece. Hold the pieces, one side at a time, against the longer middle piece, to form a solid connection.

    How to Build Bay Window Cornices
    Window cornices frame and bring in a window elegantly (interior a bedroom image by Leonid Nyshko from
  5. 5

    Use glue and pins to attach padded fabric or the fabric of your choice to the assembled foam board cornice. Glue it on from what will be the unseen back side of the cornice, and use straight pins to stitch it to the back if needed. Wrap the entire cornice assembly with the fabric; then glue and pin it at the seams.

  6. 6

    Drive two 6-penny nails, one above the other, halfway into the wall at each end of the bay window, 2 inches outside the window frame. Use two nails, driven half way into the wall, 18 inches apart, for the centre piece of the bay cornice. Six 6-penny nails support the entire cornice.

    How to Build Bay Window Cornices
    Drive the nails into the walls at a slight downard angle for increased holding strength. (nails image by Witold Krasowski from
  7. 7

    Cover each of the nail heads with glue. Press the foam board assembly, covered with padded fabric, onto the nails until the cornice is against the wall, creating a strong hold.

Tips and warnings

  • Smooth the fabric over the foam board to give it a manufactured look.
  • Hold the two end pieces of the bay cornice up to the window and attach it to be sure to get the side window angles correct.

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