No part of any mobile home or accessory building shall be parked closer than 20 feet to any other mobile home or accessory building or exceed an overall height of 15 feet. Steps with related landing, not exceeding 28 square feet of lot coverage, may project four feet into the required setback. Where a mobile home park has been totally developed prior to the adoption of this chapter or where utility systems have been installed prior to enactment and in anticipation of further development, the required setback may be five feet instead of 10 feet.