Backroom is the distance that is measured from the back wall of the garage to the door. You will need to have enough clearance for the door to open completely without hitting the wall. A standard door requires the height of the door plus 18″. For commercial doors, you will need to add an additional 23” to the height of the door for a 2″ track. If you have a 3″ track, you need to add 25″.