Barn Door Gap . If you have a gap in the bottom of the barn door you can screw a board to the bottom of the door. Third, cut a piece of door that will. Close bathroom barn door gap with weatherstripping Barn door, Diy from www.pinterest.com 10x20 feet, i think you are talking about the vertical gap between wall and door. Adding a soundproof foam block or door seal. You will have to remove the door for this process to be more accessible.