Measure the length at the top of the window to configure the measurements for the wood valance. Add two inches on both sides of the window frame to cover the curtain rods. The valance should extend out far enough to clear the front side of the rods and the folds of the curtains or drapes, approximately six inches. Determine the height of the valance to measure how far down over the top of the curtain to place the valance. A good rule of thumb is to at least make the valance as tall as it is wide.
Cut four boards to the measurements that you configured. Cut a board to cover the top of the valance, two for the sides and one for the front. Use a power miter box to cut the wood at 45-degree angles for cleaner edges.
Apply a layer of wood glue to the beveled edges of boards with a small paintbrush. Clamp the wood together overnight to allow the glue to dry completely.
Remove the clamps and use a nail gun to add finishing nails every four to six inches where the boards meet to keep the valance together.
Nail the desired trim and crown molding in place and stain or paint the wood, if desired.
Locate the studs on the wall where your valance will hang. Run the stud finder along the wall until the light indicates a stud. Nail a two-inch bracket to the wall on either side of the window on the stud to hold the valance
Place the valance on top of the bracket and secure it with 3/4-inch screws.