Backroom or rear clearance is the distance between the overhead door and the back wall of the space where the overhead door is installed. For a residential garage door the backroom required is at least the door height plus 18”. For a commercial overhead door the requirement is door height plus 23” when 2” track is used and 25” when 3” track is used. The backroom requirement is also larger if an electric opener needs to be installed behind the overhead door.