§ 27-375 Interior stairs.
AC § 27-375
Interior stairs shall comply with the following requirements: (a) Capacity. The capacity of interior stairs shall be as listed in table 6-1.
(b)Width. The width of interior stairs shall be the clear width between walls, grilles, guards, or newel posts. Stair stringers may project into the required width not more than two inches on each side of the stair. No interior stair shall be reduced in width in the direction of exit travel. Interior stairs shall be at least forty-four inches wide except as follows: (1) Interior stairs may be not less than thirty-six inches wide when serving not more than thirty occupants per stair on any floor in buildings classified in occupancy groups J-1 and J-2 or when serving buildings classified in occupancy group J-3 and exceeding four stories in height, or when serving not more than sixty occupants per stair on any floor in buildings classified in occupancy groups E, B, and D.
(2)Interior stairs may be not less than thirty inches wide when serving mezzanines having an occupant load not exceeding twenty-five persons or when located in buildings classified in occupancy group J-3 not more than three stories in height. Interior stairs in four story buildings classified in occupancy group J-3 shall be a minimum of thirty-three inches in width.
(c)Headroom. The clear headroom shall be at least seven feet, except that in buildings classified in occupancy groups J-2 and J-3, the minimum clear headroom may be six feet eight inches. Headroom in a flight of stairs shall be measured vertically between two parallel inclined planes, one of which contains the line of the nosing or upper front edge of each tread and extends to its intersection with a landing and the other of which is through any point directly above the first plane that limits the headroom of the stair.
(d)Landings and platforms. Landings and platforms shall be provided at the head and foot of each flight of stairs, except at the head of basement stairs in oneand two-family dwellings, and shall comply with the following: (1) The minimum width of landings and platforms perpendicular to the direction of travel shall be equal to at least the width of the stairs except that on a straight-run stair, the distance between risers of upper and lower flights at intermediate landings or platforms need not be more than forty-four inches.
(3)Landings and platforms shall be enclosed on sides by walls, grilles or guards at least three feet high.
(e)Risers and treads. Risers and treads shall comply with table 6-4 and with the following: (1) The sum of two risers plus one tread exclusive of nosing shall be not less than twenty-four nor more than twenty-five and one-half inches.
(4)Curving or skewed stairs may be used as exits when the tread and riser relationship is in accordance with table 6-4 when measured at a point eighteen inches in from the narrow end of the tread; and no tread shall be more than three inches narrower or three inches wider at any point than the width established eighteen inches in from the narrow end.
(f)Guards and handrails. Stairs shall have walls, grilles, or guards at the sides and shall have handrails on both sides, except that stairs less than forty-four inches wide may have a handrail on one side only. Handrails shall provide a finger clearance of one and one-half inches, and shall project not more than three and one-half inches into the required stair width.
(1)Stairs more than eighty-eight inches wide shall have intermediate handrails dividing the stairway into widths that maintain the nominal multiples of twenty-two inches, but the widths shall not be greater than eighty-eight inches nor less than forty-four inches.
(5)Handrails in all stairs shall be of materials having a flamespread rating not exceeding one hundred fifty.
(g)Stair doors. Doors providing access to stairs shall comply with the requirements of subdivision (a) of section 27-342 of article five of subchapter five of this chapter and subdivision (e) of section 27-371 of this article. The swing of stair doors shall not block stairs or stair landings, nor shall any door at any point of its swing reduce the effective width of the landing or stair to less than seventy-five percent of the required width of the landing or stair, or to less than the width of the door opening on them. The width of doors from a stair shall not be less than the number of units of exit width required for the capacity of the stair, but in no case shall the door width be less than required by subdivision (e) of section 27-371 of this article.
(h)Stair construction. Risers, treads, stringers, landings, platforms, and guards, exclusive of handrails, shall be built of noncombustible materials except that interior stairs in buildings of construction group II may be built of combustible materials in buildings classified in occupancy group B-2, C, D or E when the buildings are two stories in height or less, and in buildings classified in occupancy group J-2 or J-3 when the buildings are not more than three stories in height, and in the case of J-2 occupancy group, when occupied by not more than three families. Interior stairs shall have solid treads. All risers shall be closed except as otherwise provided in subdivision (i) of this section. When of combustible construction, the soffit of interior stairs shall be fire protected by material having a minimum fire resistive rating of one hour or five-eighths inches gypsum wall board or equivalent, or the space beneath shall be enclosed without openings by material having a one hour fire resistance rating unless permitted to have open risers by subdivision (i) of this section. Where two separate interior stairs are contained within the same enclosure (so called "scissor stairs"), each stair shall be separated from the other by noncombustible construction having a fire resistance rating equal to that required for the stair enclosure. Stairs, platforms, and landings shall be designed to support all loads in compliance with the requirements of subchapter nine of this chapter. Treads and landings shall be built of or surfaced with nonskid materials.
(i)Stair enclosures.
(6)Impact resistance. Stair enclosures serving occupancy group E spaces (office spaces) in high rise buildings constructed pursuant to applications filed on or after July 1, 2006 shall comply with rules to be promulgated by the commissioner establishing minimum impact resistance standards. Such rules shall permit compliance with assemblies comprising approved reinforced construction boards affixed onto stud framing. The commissioner shall promulgate such rules on or before January 1, 2006.
(j)Openings and obstructions to stair enclosures. No piping of any kind, with the exception of piping required or permitted in subchapter seventeen of this code, shall be permitted within a stair enclosure. No openings of any kind, other than windows, fire department access panels, exit doors and openings specifically authorized in reference standard RS 5-18 shall be permitted within a stair enclosure. Pipes required or permitted by such subchapter seventeen and protected in accordance therewith which do not reduce the required clearances of the enclosure may be permitted. Ducts protected in accordance with the requirements of subchapter thirteen of this chapter, which do not reduce the required clearances of the enclosure, may be permitted. In addition, in buildings in occupancy group J-2, which are three stories or less in height and occupied by not more than two families on each story, a door from an apartment may open directly into a stair, and the door may swing into the apartment.
(k)Roof access.
(l)Spiral stairs. Spiral stairs may serve as access stairs between two floors or levels in accordance with the provisions of paragraph two of subdivision (i) of this section. Such stairs may not serve as required exits, except that unenclosed spiral stairs when built of noncombustible materials and having a tread length of at least thirty inches may serve as exits from mezzanines or balconies having an occupant load not exceeding twenty-five persons. TABLE 6-4Maximum Riser Height and Minimum Tread Width Occupancy Group Classification of BuildingMaximum Riser Height (in.)Minimum Tread 1 Width (in.)Residential J-3 (with closed risers) 8 1/49 plus 1 1/4 nosingResidential J-3 (with open risers) 8 1/49 plus 1/2 nosingResidential J-2 (with only three dwelling units) 8 1/49 plus 1 1/4 nosingAssembly F 7 1/2 9 1/2 plus nosingInstitutional H-2 7 10 plus nosingAll others 2 7 3/4 9 1/2 plus nosingNotes for Table 6-4: 1 Treads may be undercut a distance equal to the nosing. A nosing shall not be required when tread width is eleven inches or wider. 2 The proportions and dimensions of treads and risers may be adjusted in buildings classified in occupancy group G to suit the age of occupants, subject to the approval of the commissioner.
