To make a box pleat valance, measure and cut the fabric, measure and fold the pleats, line them up to the board and staple into place. Making a box pleat valance takes roughly 1 hour and requires enough fabric and liner plus 8-inch pleat allowance to cover the window, a 2-by-4 piece of wood, a sewing machine, a staple gun, a tape measure, sewing scissors, a pen, pins and thread that matches the fabric.
- Measure the fabric
The board for the box should be 2 inches longer than the width of the window. When measuring the fabric, factor in 8 inches for each pleat, 3 inches on either side to go around the board and a half-inch seam allowance all the way around. For length, add 3 inches to wrap over the top and a seam allowance of a half-inch in addition to whatever length you want the finished valance to measure.
- Cut the fabric
Mark the fabric on the back side according to your measurements. Using sewing scissors, cut the fabric while it is lying flat on a table.
- Line the fabric
Cut the lining to the same size. Pin the fabric and lining so that the fronts are facing each other. Sew a half-inch seam all the way around, leaving a 2-inch gap in one corner. Pull the fabric through and sew the seam closed. Iron the seams flat.
- Measure for placement on the board
Mark the center of the fabric with a pin and the center of the board with a pen. Mark halfway down either side of both the fabric and the board, which is where the center of each pleat goes.
- Fold the pleat
Fold one side of the fabric in to the pin marking the center of the pleat, then fold it back out. Repeat on the other side, and measure. Each side of the pleat should be 2 inches. If the pleat is even, press it into place with the iron. Repeat the procedure for the other pleat.
- Sew the pleat
Measure 6 inches down the length of each pleat. Sew as close as possible to the inner edge of either side of the pleat from the top to the 6-inch mark.
- Staple the fabric
Lay the board flat. Line up the pins with the marks on the board. Staple the fabric, placing a staple on either side of the pleat and every 2 inches across the top. Wrap the fabric around the ends of the board to the back. Staple it into place.
- Wrap and staple the end piece
As if wrapping the side of a present, fold the side of the fabric over the top piece. Secure in back with a staple.