In order to fully understand how to hang a cornice, let’s look at exactly what the purpose of a cornice is. A cornice is basically a decorative box made up of a top, a front, and two sides. Its purpose is to hang above a window to hide a curtain rod and hooks. It also makes the room look more elegant and will add value to your home when the time comes to sell it.
Tools and materials you will need are a saw (Skil saw or table saw), a framing square, miter saw, screw driver or electric drill with a # 2 screw bit, four foot level, wood glue, drywall screws, brad nail gun, 2 “L” brackets, caulk or wood putty, sandpaper, and 2 butterfly bolts.
The cornice must be large enough to remain clear of the drapery hardware and not hinder its operation. It should be wide enough to be proportional to the window it is above, and high enough to hide the curtain rod, curtain hooks, hardware, etc. People in the design business recommend the height to be one fifth the length of the curtains to get the proper look. Once you have your dimensions, cut your plywood to size.
Attach the sides of the cornice board to the front using quality wood glue. Now use either screws or a brad nailer to secure it. Repeat to add the top piece to the front and side piece you just assembled.
Once you have finished the box part, you will want to attach crown molding on the top front and sides. Cut the right and left front corners at a forty five degree miter and cut the back flush with the back of the box where it will meet the wall. On the bottom edge of the box, attach “L” trim to conceal the end grain of the plywood. Cut the corners the same way you did the crown molding.
At this point you should be ready to finish it however you like. You might paint it, stain it, upholster it, or apply fabric to it. It all depends on the look and style of your room. Before you finish it, be sure to fill all the nail and screw holes with caulk or wood putty and sand it smooth. Also, use it to tidy up your miter joints.
You are now ready to hang your cornice. Determine where the inside corner of the cornice will be on one side of the window at least one inch above the curtain rods so their operation will not be hindered.
Mark the spot and use your four foot level to transfer that mark to the other side of the window. What we are doing here as you might guess is making sure the cornice will be level. You can’t trust the window.
Attach the two “L” brackets to the wall on the spots you have marked. If you are lucky enough to hit studs (and you might hit some framing this close to the window) go ahead and use drywall screws. If you just have empty space behind the sheetrock, use the butterfly bolts.
Then place the cornice board in position and attach the board to the secured brackets. Now you are all done and your cornice is ready for your viewing pleasure.