(1) The clear height over stairs shall be measured vertically, over the clear width of the stair, from a straight line tangent to the tread and landing nosings to the lowest point above.
(2) Except as provided in Sentence (3) and Article 9.8.4.5A., the clear height over stairs shall not be less than 2 050 mm.
(3) Except as provided in Article 9.8.4.5A., the clear height over stairs serving a house or an individual dwelling unit shall not be less than 1 950 mm.