To build a wooden valance, often called a window cornice, first decide on a design that matches the decor and existing molding in the home. Measure the curtain rod with the curtains on and open to account for the full extent of the fabric. Add an inch to both the depth and width to ensure the valance provides full coverage. Square the board with a miter saw. Attach the mitered corners with both glue and nails to form the valance.
Measure the top of the valance and cut a board to fit that measurement. Apply any necessary trim or molding by starting with end pieces and mitering them closely at the corner. Fill any visible nail holes or gaps in the mitered corners with wood filler, sand down the excess, and file the miters to smooth the wood. Prime the valance, and then paint the desired color. Depending on the trim added, light coats of spray paint until full coverage is achieved may be more effective than using a brush.
To hang the wooden valance, center it over the curtain rod and open curtains. Reach beneath the valance and mark the bottom of the valance. Use a level to determine a straight line, and then cut a 1-inch by 2-inch board to fit between the rod brackets. Screw it into the wall and drill 1/8 inch holes through the top of the valance and into the board attached to the wall.