How to Build a Curtain Box

Measure the distance from one top corner of the window to the opposite top corner to determine the width of the cornice front. Add 1 inch before recording it. Draw the curtains open when measuring their depth, add 1 inch and record this measurement for the two short side pieces of the cornice.

Cut a 1-by-8-inch piece of wood for the back of the cornice using a miter saw. Set the saw at 45 degrees and bevel cut the ends of this board. Cut the side pieces according to your depth measurement and cut one end of each side piece at 45 degrees. Reset the miter saw to 90 degrees and cut the side pieces to the noted length.

Dab or spray wood adhesive on the mitered ends of the long board. Position each side piece, ensuring the mitered ends meet to form square corners. Press each joint to help the glue set. Allow the glue on the cornice to dry for the time specified on the label instructions.

Insert a row of three 1-inch brads from each side to secure the small boards to the long board.

Measure the width and length of open top of the cornice. Mark the measurements on a 1-by-8-inch lumber. Cut along the lines with a handsaw.

Center the board over the exposed cavity to determine its size. Ideally, if required, trim excess length or width so its sides fall flush with the three sides of the cornice. Lift this board and set it aside.

Dab or spray wood glue over the exposed upper edges of the front and two sides. Center and lower the top board over the glued sections. Press the board to form a secure bond with the glue and leave it to set for the time specified on the label directions.