How to Make a Window Cornice

DIY Window Cornice, picture of a curtain with sun shadows

A couple of months ago I showed you how to make a no-sew window swag.  If you want a more architectural window treatment, and still don’t want to sew, it’s time to consider DIY window cornice. Once again, you’ll need power tools and lumber, but you won’t have to sew. I used instructions I found at Lowe’s, but I discovered along the way that some modifications were necessary, so here’s my version of the instructions for building a window cornice.

Window Cornice Materials

1/4-inch Lauan plywood
1×2 mounting board
Staple gun and staples
¾” Wood screws
1 or 2-inch L brackets
Wood glue
Circular saw
Measuring tape
L or T square
Marking pen or pencil
Drywall screws
Electric screwdriver

Steps on How to Make a Window Cornice

1. In Building a Window Cornice you must first need to measure the window.

Take the following measurements: width including frames or window treatments that extend beyond the edge of the frame, depth including window treatments that extend beyond the edge of the frame, height of window treatments you want to cover or window frame.

Now add to each of those measurements. Example: I added 4 inches to the window width to allow room for mounting. We don’t have window frames, so I measured the height of the blind cornice and added 4-6 inches to give it some drama. My cornice sticks out half an inch, then I added 2 inches to the depth.

Write down your measurements. Determine the number of cornices you’ll be making and figure out how many pieces of 4×8 foot Lauan you’ll need. You’ll be cutting a cornice front that is the width of the cornice by the height of the cornice and two cornice sides that are the depth of the cornice by the height of the cornice. For example, one 60×8 piece and two 3×8 pieces.

2. Measure out the cleats.

If you use Luan, you’ll need to make mounting cleats out of 1×2 pine. If your cornice is less than 3 inches deep, make 1 inch wide by 2 inch tall cleats. If your cornice is more than 3 inches deep, make 2×2 cleats. Each cornice will require four cleats. Buy enough wood to have some overage for mistakes. If you make 2×2 cleats, you can use 2-inch mounting brackets rather than 1-inch.

3. Measure and cut the wood.

Sand all the edges smooth.

4. Lay the cornice front flat.

Measure half an inch in from the left and right edges and make a line. Measure half an inch down from each of the edges and make a line. Glue one cleat in each corner. If you’re using 1×2 cleats, the long side of the cleat is parallel to the short edge of the cornice front.

5. Lay the cornice sides flat.

Measure half an inch from the left edge of the left cornice side and half an inch from the top. Mark these lines. Repeat half an inch from the right edge of the right cornice side and half an inch from the top. Glue one cleat to each cornice side. Let dry.

6. Turn over the cornice front and sides.

Screw through the Luan into the cleats to secure in place.

7. Turn over again.

Run a line of glue along the left edge of the cornice front. Attach the cornice side to this line of glue, perpendicular to the front, and flush with the mounting cleat. The mounting cleats should also be perpendicular. Hold until dry. Repeat on right side.

(See photo in step 11 for example. There are cleats at each end in the photo, but this was because of a mistake.)

8. Screw from the outside of the cornice side into the mounting cleat attached to the cornice front.

9. Measure the length of your DIY window cornice from side to side, allowing wrap-around.

For a 60-inch wide cornice with 3-inch sides, this is 66 inches. Add 6 inches for batting and wrapping. Add 6 inches to the height for batting and wrapping. My total fabric size was 72 inches by 12 inches.

10. Iron the fabric.

11. Cut the fabric and the batting to the appropriate size.

Turn the fabric wrong side up. Lay the batting on top of the fabric. Center the cornice on top of that. Pull the fabric taut against the bottom edge. Staple in the center. Repeat at the top. Move to one side. Pull the fabric over the side and pull taut. Staple in the center. Repeat on the other side. Now staple every few inches along each side. Pull taut before each staple. Trim overage. You may need to stitch or hot glue the outer corners so the fabric doesn’t bunch where it presses against the wall.

If the back of the cornice will be visible from outside the window, hot blue glue an unpadded piece of the fabric to the inside of the cornice.

12. Measure from the middle of each mounting cleat.

Mark this width on the wall. Hold up the cornice to make sure it’s centered and level. Mark the edges to confirm. Drill starter holes in the wall and each cleat. Mount one L-bracket to the wall with a drywall screw. Align the cornice cleat with the L-bracket, and screw the bracket to the cleat with a wood screw. Check leveling and centering again and repeat on the other side.

You’re done. The total cost was about $60. My fabric was $10 a yard and the batting was $1 a yard, but I have access to cheap fabric. Without the fabric, the materials were around $30, not counting the tools I had to buy that I didn’t already have.

My dad proposed a couple of alternatives to this. When they made their cornices, they used 1×10 mounting board rather than Lauan and held them together with L-brackets rather than cleats. Although this is easier, it will be heavier, so you make sure you can mount the cornices to studs.

If you use Lauan and cleats, he suggested that we could have hung mounting hooks on the wall, attached hooks to the cleats, and simply hung the cornices on them instead of screwing them to the wall. Visit the hardware store and see what looks useful to you.

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