Abstract: A modular, double-height animal boarding system which can be installed inside a building having limited headroom while permitting persons up to six feet in height to enter lower runs without stooping. The boarding system has a lower section divided into plural lower runs, each lower run having a rear wall and a door that opens outwardly away from the rear wall. At least one upper section is supported above the lower section and is divided into plural upper runs. The upper runs have doors that open onto a catwalk. The upper sections are provided with a plumbing system so that each upper run has a drain through which waste can be washed, the waste from each run then draining into a single drainpipe, and, thereafter, draining into a floor gutter connected to any suitable waste collection system. The upper runs have floors which are sealed against leakage of liquid material to the lower runs by a floor seal provided around the perimeter of the floors.