The ceiling height of any habitable room shall be
at least seven feet, except that in any habitable room under a sloping
ceiling, at least 1/2 of the floor area shall have a ceiling height
of at least seven feet, and the floor area of that part of the room
where the ceiling height is less than five feet shall not be considered
as part of the floor area in computing the total floor area of the
room for the purpose of determining the maximum permissible occupancy.