How to Build DIY Window Cornices

Updated: Sep. 21, 2023

Custom-build DIY window cornices for one-fourth the price of store-bought with this step-by-step guide.

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Want to give a dreary room a dramatic facelift? Adding window or door cornices will bring freshness and style to any room decor. They'll hide ugly drapery rods and add a touch of custom-made detailing that makes an ordinary window or patio door look like something special. The top of the cornice can even serve as a display shelf for art or collectibles.

Cornices are surprisingly easy to build, even the elegant ones you see in home magazines. Using off-the-shelf trim from the home center and a compound miter saw, anyone with simple carpentry skills can create a beautiful window or door cornice in just a few hours.

Read on and we'll show you how to select the materials, assemble the parts and attach the cornice to the wall. We'll also share design tips to help you match a cornice style to your home decor. Search online for cornice suppliers and you'll see that you can save huge money by building your own.

Tools Required

  • Air Powered Brad Nail Gun
  • Cordless drill override and 1/8-in. bit.
  • File
  • Miter saw
  • Paintbrush
  • Safety glasses
  • Screw gun
  • Tape measure

Materials Required

  • 2-1/2-in. wood screws
  • Glue
  • Paint or stain
  • Sandpaper (fine)
  • Wood filler

Design the Cornices to Fit Your Home

All wood cornices begin the same way, with cutting and assembling the three-sided, lidded box. Then you add the trim of your choice and finish the cornice. The cornice is then ready for mounting on the wall by affixing it to a 1×2 that’s screwed to the wall above the opening.

Finished cornice close-up

Finished Cornice Close UpFAMILY HANDYMAN

Cornice Cross Section And PartsFAMILY HANDYMAN

Cornice cross-section and parts

Design elements within your home should dictate the wood type, molding style and finish you select. Depending on the design, the top overlaps the sides, sometimes with a routed edge, or is nailed to the top or inside of the box and doesn’t show from below.

The tops are best made from 1x4s, 1x6s or 1x8s. There’s no need to cut the tops to width if you choose the right combination of top style and board size. The example we show is a 1×6 nailed on top of the box, which gives an overall inside depth of 4-3/4-in.

For the same look but with a shallower box, you could also nail a 1×4 inside the box flush with the top for a depth of 3-1/2-in. Choose whichever method it takes to clear your curtains.

Other cornice options

Options are almost endless. If you’re having trouble choosing, here’s a tip:

Buy short lengths of different types of trim, along with some cheap 1x4s and 1x6s. Cut everything to 1-ft. lengths and mock up several combinations. Just squirt a little wood glue on the pieces and clamp them together for about 10 minutes. Hold the cornice mock-ups over the opening to get a feel for the final look.

Fh03jau Wincor 20 21 1FAMILY HANDYMAN

Fh03jau Wincor 22 23 2FAMILY HANDYMAN

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Select Materials and Collect Key Tools

If you plan to paint your cornices, poplar and aspen are good choices for the box materials. They’re stable and cheap, and the grain won’t show through paint. Pine and basswood moldings are usually the least expensive choices for paintable trim.

If you want stained or natural wood cornices, look for oak, mahogany, cherry, maple and others at home centers. The biggest problem is finding hardwood moldings other than oak. You may have to special order them or find a specialty millwork supplier online.

The best tools for cutting miters on wide boards (1x6s) are a 10-in. compound miter saw or a sliding compound saw. Standard compound saws work like typical miter saws, but the motor and blade tip sideways, making them capable of cutting bevels. A sliding compound miter saw cuts compound angles too, but the motor and blade slide on tracks so it can handle wider stock.

Be sure to use a sharp finish-cutting blade in either one. Prices for standard compound miter saws are low, or you can rent one.

You can pre-drill and hand-nail most of the project, but an air-powered brad nailer with 1- and 1-1/2-in. brads makes the job much easier. Many are inexpensive and well worth the price. Or you can rent one. (Go with one of the special airless ones and you’ll save the price of renting a compressor.)

But for the money, compound miter saws and brad nailers are far too useful and far too fun not to own yourself.

Project step-by-step (14)

Step 1

Measure carefully

Begin by measuring the curtain and curtain rod for length, depth and width. Measure with the curtains open so you account for their thickness when bunched. Add an inch or so to the depth and the width of the curtain rod to make sure the cornices will cover everything.

Measure CarefullyFAMILY HANDYMAN

Step 2

Cut the boards

Miter the ends and front box pieces first. It’s easiest to square up the board, tilt the miter saw to cut a 45-degree bevel for the first end piece, then square it up to cut the second end. The mitered corners are glued and nailed together with 1-in. brads. Measure the assembly to determine the exact length of the top.


Step 3

Join the boards

Smear wood glue on the miters and tack the joint together with six 1-in. brads, three from each side.


Step 4

Attach the top

Cut the top board to length to fit flush with the front and sides of the box, depending on the design. Glue and nail the top to the box frame with 1-1/2-in. brads spaced every six inches.


Step 5

Fit the trim

When mitering the trim for the box, always start by cutting and mounting an end trim piece, then the long front trim and finally the other end. That way, you can check fits and get crisp miters at each corner.

Fit each miter, then scribe the length of each piece rather than measuring. It’s faster and much more accurate. It’s best to cut pieces a tad long so you can shave them down until they fit perfectly. If you’re new to woodworking, it’s nice to have a helper by your side to hold the miters together while you’re scribing lengths or fastening parts.

Using a short test piece, fit the end piece and mark and cut it to fit. Use the test piece to accurately position the trim while you glue and nail it to the box. Cut the miter on the long front piece of trim, fit it to the first piece, mark its length, then cut and fasten it. Repeat the steps for the other end.


Step 6

Cut the end pieces

Cut the two crown molding end pieces 1-in. longer than needed with opposite 45-degree angles on one end of each piece (you’re cutting a right and a left corner).

The trick to cutting crown molding miters is resting the molding upside down and against the bed and fence while cutting the 45-degree angles. If you cut wide crown molding, you may have to extend the fence height by screwing a length of 1×4 to the miter saw fence through the holes in the back.

Remember, the long point of the miter is always the top edge. That will help you remember which way to angle the saw before cutting. To further eliminate the costly mistake of miscutting an angle, draw a light line while you’re fitting the piece to indicate the proper angle.

Pro tip: Build up short fences to support crown moldings while cutting by screwing 1×4 boards to the saw fence through the predrilled holes in the fence (shown above).


Step 7

Attach the crown molding

Flip the box upside down and prop the crown molding endpiece against the box. Use the other end as a test piece to line up the miters. Mark and cut the piece to length. Smear a little glue along the bottom and tack it to the cornices with a couple of 1-in. brads.

Fh03jau Wincor 11 Attach The Crown MoldingFAMILY HANDYMAN

Step 8

Finish installing the crown molding

Test-fit, mark and cut the front piece of crown molding to length. Glue and nail the miters together, then nail the molding to the cornice box. Cut and install the last end piece of crown molding.

Finish Installing The Crown MoldingFAMILY HANDYMAN

Step 9

Install the bottom trim

Cut, fit, glue and nail the bottom piece of trim to the box using the same techniques you did with the crown molding.

Install The Bottom TrimFAMILY HANDYMAN

Step 10

Smooth out the profiles

Fill nail holes and any miter gaps in joints with wood filler. Sand excess wood filler and file miters as necessary to remove any wood fibers or smooth out inconsistencies in profiles.

Smooth Out The ProfilesFAMILY HANDYMAN

Step 11

Prime the wood

Fill nail holes and prime before painting. If your cornices have elaborate details like dentil blocking, you’ll get better results with several light coats of spray paint instead of brushing. Finish highly detailed natural and stained wood with spray lacquer, shellac or polyurethane.

Prime the wood and lightly sand it with 150-grit sandpaper before applying your choice of paint.


Step 12

Center the cornice

Center the cornice over the opening at the height that best covers the curtain rod and curtain. Then reach underneath and mark the bottom. Take down the cornice and extend the mark with a 4-ft. level.


Step 13

Install the ledger

Cut a 1×2 to fit between the curtain rod brackets. Screw it through the drywall into the framing with 2-1/2-in. screws spaced about every foot. Pre-paint the 1×2 cornice ledger to match the wall before you put it up if you think it will show after the window covering is in place.


Step 14

Drill pilot holes

Pre-drill 1/8-in. pilot holes spaced about every foot in the top of the cornice 3/4-in. from the back edge. Angle the holes slightly toward the wall. Hold the cornice tight to the wall and run 2-in. screws into the 1×2.