StairwellsTip 18: Boxing in a basement stairwell 1. Nail 1" x 3" cleats onto the ceiling joists. The distance from the old ceiling height to the new ceiling height will determine the width of the valance material. 1" x 4" or 1" x 6" white pine is most commonly used.  2. Nail valance into cleats. 3. Cover the seam with standard flat molding. 4. Install the appropriate wall molding at the height desired. |