(1) Except as provided in Sentence (2) and Article 9.8.4.5A., required exit stairs and public stairs serving buildings of residential occupancy shall have a width, measured between wall faces or guards, of not less than 900 mm.
(2) Required exit stairs serving a house or an individual dwelling unit shall have a width of not less than 860 mm.
(3) Except as provided in Article 9.8.4.5A., required exit stairs and public stairs serving buildings of other than residential occupancy shall have a width of not less than the greater of,
(a) 900 mm, or
(b) 8 mm per person based on the occupant load limits specified in Table 3.1.17.1.
(4) Except as provided in Article 9.8.4.5A., at least one stair between each floor level within a dwelling unit and exterior stairs serving a house or an individual dwelling unit shall have a width of not less than 860 mm.