(1) Except as provided in Sentence (2), the distance between a stair riser and the leading edge of a door in its swing, except for doors serving a house or an individual dwelling unit, shall be not less than 300 mm.
(2) Where there is a danger of blockage from ice or snow, an exit door, including a door serving a house or an individual dwelling unit, may open onto not more than one step provided the riser of such step does not exceed 150 mm.