How to Build and Hang a Window Cornice
13 min read
Learn how to build your own wood window cornice box to dress up your window frame. Building a custom wood window valance is a great beginner building project!
See more of self-taught DIYer Jenny’s home and tips for beginning DIYers here — you won’t want to miss her beautiful kitchen and living room! Plus read how to install easy craftsman window trim around any window.
What is a Window Cornice?
A window cornice is a 3-sided box that frames the top of a window. A cornice typically covers—and extends out over—curtain rods, the top section of blinds, and window casings. It can be as tall as you care to make it, simple or fancy.
A window cornice is typically solid, like these made from wood in this tutorial, while a window valance is traditionally made from fabric and more like a short curtain at the top of the window. A wood window valance “box” might also be called a pelmet box, which is typically more solid than a valance but covered in fabric to match the drapery.
Whether you call it a window cornice, valance, or pelmet, the purpose is to cover up the window hardware and give your windows some presence and style!
Creative Window Cornice Ideas
Get creative with window cornices to fit the function and style of your room. Some ideas:
- Add a shelf to the top for displaying stuffed animals or kids’ soccer trophies.
- Paint the box portion of the cornice a different color than the trim portions.
- Paint the window casing the same color as your cornice or vice versa.
- Layer trim pieces to get a distinctive look or use a router to create a really custom piece.
- And, if you’re putting crown molding up in the room at the same time as you’re doing your cornices, you can design it so that the crown molding runs seamlessly around the room and the window cornice—-heaven!
For my wood window cornices, I used crown molding that matched what was already in the room —- pretty standard builder-grade stuff that you can find at any big box store. I also used some ogee trim (also known as base cap).
How to Build a DIY Wood Window Cornice
Please keep in mind that all of these wood dimensions and trim pieces are specific to my cornices—-you may want to do something different. For example, I used a 1″ x 8″ board for my cornice box, but if you want a taller (or shorter) cornice box, you’d want to buy a wider, or shorter, board, etc.
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Wood Window Cornice SUPPLY LIST
*This is a soft and inexpensive wood. It often has knots and is sometimes not straight, so be choosy when selecting your wood. Get the straightest possible pieces with the fewest knots. You can use a harder and higher-quality wood, but it will be more expensive; if you plan to stain your cornice, rather than paint it, you’ll likely want to invest in a higher-quality wood species.
Wood Window Cornice TOOL LIST
DIY Wood Window Cornice Box Assembly
STEP 1: Plan & Measure
Plan the look of your cornice. Consider:
- What trim, if any, do you want to use?
- Will you stain it or paint it?
- How tall and wide do you want it to be?
- How much space do you have above and on the sides of the window to work with?
Measure your window from the outside edge of the window casing on one side to the outside edge of the window casing on the opposite side. Do not measure just the window by itself. Include the casings!
Your cornice will hang down over the window and the casings. I chose to add 4″ (that’s 2″ for each side of the window) to my window measurements. Why? To allow for the width of the edge of the cornice and for a little space between the window casing and the cornice.
Helpful Reading: Universal Tricks for Good Looking Curtains
Also measure out from the wall to determine how deep your cornice needs to be. Will the cornice hang over a curtain rod or blinds? The cornice box needs to be deep enough to extend out over any obstacles—-the window casing, blinds, or curtains.
Add at least a 1/2″ or so to your depth measurement so you won’t have to worry about your cornice scraping up against your window treatments after it’s installed.
Based on the clearance you have between the ceiling and your window, as well as your personal preference, determine how tall you want your cornice to be.
Purchase your materials and make a sketch of your dimensions.
STEP 2: Cut the Wood Cornice Pieces & Crown Molding
I cut all the pieces for my cornice first.
I cut my 1″ x 8″ common board to length and cut both of the short sides at a beveled 45-degree angle using a miter saw. This piece is the front of your cornice box.
For the top and side pieces of my cornice box, I needed a shallower width of board, so I ripped my 1″ x 6″ common board down to 1″ x 5″ (a non-standard size not available at my local lumber yard) using a table saw. I then cut the top and side pieces of my cornice box from the 1″ x 5″ board.
For the side pieces, I used my miter saw to cut 45-degree angles on one of the long edges.
I cut my crown molding and ogee trim, both the front and side pieces, mitered to meet flush at the corners of the cornice box.
See this post for tips and resources to help you learn how to cut crown molding and other trim — and always remember to practice, practice, practice on some inexpensive molding or scraps until you’re confident with your cuts.
For the ogee trim, set your table to 45-degrees. Leave your blade on center at 0-degrees.
For the crown molding, you’ll need to set the angles on your blade and table according to the spring angle of the crown molding you’re using. I used just about the most basic and widely available crown molding there is (spring angle: 53/37). I set my miter (angle on table) to 31.5-degrees and my bevel (tilt of blade) to 34-degrees.
The largest piece of crown molding, running along the top of the cornice box, has 2 outside corners.
The left-hand mitered outside corner is cut by placing the crown to the right of the blade. The top edge of the crown rests up against the fence. The miter angle on the table of your miter saw is set to the right of center.
You will also cut the right-hand side piece of crown this way. The edge of the side piece of crown that meets the front piece of crown will be cut at an angle. The other side will be flush against the wall, so it’s a straight-edge cut.
The right-hand mitered outside corner is cut by placing the crown to the right of the blade. The bottom edge of the crown rests up against the fence. The miter angle on the table of your miter saw is set to the left of center.
You will also cut the left-hand side piece of crown this way. The edge of the side piece of crown that meets the front piece of crown will be cut at an angle. The other side will be flush against the wall, so it’s a straight-edge cut.
When cutting crown, I always add a half-inch or a little more to the total length I measured before cutting. I’ll do a test fit after making my first cut and then trim a little more off if I need to, but with crown, once you cut it too short, you’re out of luck! So I’m always very, very careful and take my time to be sure to get it right. Keep in mind, too, that crown has to extend a bit past the length of your cornice box. If the cut edge of the crown lines up exactly with the edge of the cornice box, there won’t be enough of an edge left on the crown to meet up with the edge of the side piece of crown, which you’ll want it to do in order to get a neat corner.
STEP 3: Assemble the Wood Cornice
I drilled holes using my Kreg Jig along the top, inside edges of my front box piece and my 2 side box pieces. (If you don’t own a Kreg Jig, you can join your box together by first gluing with wood glue and then using finishing nails or a nail gun.)
I used wood glue to join the mitered edges of my side box pieces and my front box piece and clamped it all to dry. Then, I used my 18-gauge nail gun to reinforce the bond by nailing the pieces together (you could also use a hammer and finishing nails, if you don’t have a nail gun).
Next, I used my Kreg Jig screws to screw together the top piece of my box to the front and side box pieces. Now, you’ve got yourself a box. Time to jazz it up!
STEP 4: Attach Cornice Trim
I attached the ogee trim flush to the bottom edge of my cornice box with my 18-gauge nail gun (you can also use finishing nails and a hammer). You can glue first, too, if you’d like to.
Before attaching any trim, though, test the fit of your corner pieces to make sure they fit together properly. 
Make measured marks all along the length of your box where you want your crown molding to be. Then, use a level or other straight edge to connect the marks so you have a line along which to line up the bottom edge of your crown molding—you want it to be level. Nail along the bottom edge of your crown to attach it to your cornice box. It can be anywhere on the box frame you choose for it to be—-flush with the top edge of the box or somewhere farther down the box. I chose to have a 5-1/2″ gap between the top of my ogee trim and the bottom of my crown molding.
You can always add a shelf to the top of the cornice box, which would give the crown something to attach to (like it would if it were being fitted along a wall and ceiling), but since on this cornice, I chose not to add a shelf, I had to glue the corner crown pieces to the center crown piece to attach them.
Use painter’s tape to secure the connection until the glue dries. Attach the bottom of the side pieces of crown with nails along the bottom edge, just as you did with the front piece of crown.
I would advise against trying to nail the top piece of the side crown to the top piece of the front crown, as you’ll risk splitting the crown.
STEP 5: Finish and Paint Your Window Cornice
Now, use wood filler on your nail holes and caulk all the seams.
Helpful Reading: Tips for Caulking Like a Pro
After the wood filler and caulk have dried, do a light sanding to ensure a smooth finished surface. Wipe away all dust and debris.
I used one coat of primer and two coats of paint, letting everything dry thoroughly between coats.
Remember to paint the underside of your cornice box, too, as it will be visible if someone is standing close to, or under, the window.
If the top of your cornice box will be visible, be sure to paint the top, too, but most of the time, a cornice box will be so close to the ceiling that no one will be able to see the top of it.
How to Hang a Wood Window Cornice
Cut a 1″ x 2″ strip of wood just shorter than the full length of your completed cornice box.
Mount it to the wall above the window where you’ll be hanging the cornice, using a level and 2″ wood screws. Be sure to attach to studs and not just dry wall.
Keep in mind how far down over your window you want your cornice to hang—-that will determine where on the wall you install the 1″ x 2″ strip of wood (your cornice box will ‘hang’ on this strip of wood).
You will attach your window cornice box by ‘hanging’ it on, and screwing it in to, your 1″ x 2″ strip, which you have mounted to the wall above your window. It won’t be secure enough to just ‘hang’ the cornice box on the 1″ x 2″ strip. You need to screw down through the top of the cornice box, in to the 1″ x 2″ strip at regular intervals along the length of the cornice box.
To make the job easier, I screwed my 2″ wood screws partially in to the top of my cornice box before hanging it, so that I’d have less screwing to do after putting the cornice box in place over the window. Be mindful in the placement of your screws. You don’t want them so close to the edge that the wood splits, thus compromising the attachment. Neither do you don’t want them so far away from the edge that they won’t screw down in to the top of your wall-mounted 1″ x 2″ strip.
You can also use the same concept to create a decorative and/or functional shelf.
Instead of making a box as you did for the cornice, use just a flat board and add a shelf on top. Attach trim just as you would for the window cornice. I used an Ook Hangman French Cleat Picture Hanging Kit to hang the shelf below in my kitchen—-works like a dream! And, yes, you can hang it somewhere other than over a window!
Or use the same idea to create a bed crown cornice like Cassity did for her daughter’s room here:
More ways to make your windows look amazing:
DIY Window Cornice Before and Afters
And just for kicks and giggles, here’s what those bedrooms looked like when we bought the house and what they look like now (with the window cornices and other updates):
Be sure to pin your favorites to save for later and share with your friends!
Published 05.03.16 // Updated 05.14.20
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