The Minnesota State Building Code applies to residential buildings in
Saint Paul. In particular, 1309.0314 Section R314, which is hereby
quoted in full:
R314.1 Width. Stairways shall not be less than 36 inches (914
mm) in clear width at all points above the permitted handrail
height and below the required headroom height. Handrails shall
not project more than 4.5 inches (114 mm) on either side of the
stairway and the minimum clear width of the stairway at and
below the handrail height, including treads and landings, shall
not be less than 31.5 inches (787 mm) where a handrail is
installed on one side and 27 inches (698 mm) where handrails are
provided on both sides.
Exception: The width of spiral stairways shall be in
accordance with Section R314.5.
R314.2 Treads and risers. The maximum riser height shall be 8
inches (203 mm) and the minimum tread depth shall be 9 inches
(228 mm). The riser height shall be measured vertically between
leading edges of the adjacent treads. The tread depth shall be
measured horizontally between the vertical planes of the
foremost projection of adjacent treads and at a right angle to
the tread's leading edge. The walking surface of treads and
landings of a stairway shall be sloped no steeper than one unit
vertical in 48 units horizontal (2-percent slope). The greatest
riser height within any flight of stairs shall not exceed the
smallest by more than 3/8 inch (9.5 mm). The greatest tread
depth within any flight of stairs shall not exceed the smallest
by more than 3/8 inch (9.5 mm).
R314.2.1 Profile. Open risers are permitted, provided that the
opening between treads does not permit the passage of a 4 inch
diameter (102 mm) sphere.
R314.3 Headroom. The minimum headroom in all parts of the
stairway shall not be less than 6 feet, 8 inches (2032 mm)
measured vertically from the sloped plane adjoining the tread
nosing or from the floor surface of the landing or platform.
R314.4 Winders. Winders are permitted, provided that the width
of the tread at a point not more than 12 inches (305 mm) from
the side where the treads are narrower is not less than 9 inches
(228 mm) and the minimum width of any tread is not less than 6
inches (152 mm). The continuous handrail required by Section
R315.1 shall be located on the side where the tread is narrower.
R314.5 Spiral stairs. Spiral stairways are permitted, provided
the minimum width shall be 26 inches (660 mm) with each tread
having a 7-1/2 inch (190 mm) minimum tread width at 12 inches
(305 mm) from the narrow edge. All treads shall be identical,
and the rise shall be no more than 9-1/2 inches (214 mm). A
minimum headroom of 6 feet, 6 inches (1982 mm) shall be provided.
R314.6 Circular stairways. Circular stairways shall have a
tread depth at a point not more than 12 inches (305 mm) from the
side where the treads are narrower of not less than 10 inches
(254 mm) and the minimum depth of any tread shall not be less
than 6 inches (152 mm). Tread depth at any walking line,
measured a consistent distance from a side of the stairway,
shall be uniform as specified in Section R314.2.
R314.7 Illumination. All stairs shall be provided with
illumination in accordance with Section R303.4.
R314.8 Under stair protection. Enclosed accessible space under
stairs shall have walls, under stair surface, and any soffits
protected on the enclosed side with 1/2-inch (12.7 mm) gypsum
R314.9 Bulkhead enclosure stairways. Stairways serving bulkhead
enclosures that are not part of the required building egress and
providing access from the outside grade level to the basement
shall be exempt from the requirements of Sections R312, R314,
and R315 when the maximum height from the basement finished
floor level to grade adjacent to the stairway is covered by a
bulkhead enclosure with hinged doors or other approved means.
Hope this is what you needed to know!
Minnesota Office of the Revisor of Statutes: Minnesota Rules, Chapter 1309
Minnesota Department of Labor and Industry: Minnesota State Building Code