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BUILDING PLANNING than the top of the threshold. The floor or landing at exterior doors other than the exit door required by Section R311.4.1 shall not be required to comply with this requirement but shall have a rise no greater than that permitted in Section R311.5.3. Exception: The landing at an exterior doorway shall not be more than 73/,, inches (196 mm) below the top of the threshold, provided the door, other than an exte- rior storm or screen door does not swing over the land- ing. The width of each landing shall not be less than the door served. Every landing shall have a minimum dimension of 36 inches (914 mm) measured in the direction of travel. R311.4.4 Type of lock or latch. All egress doors shall be readily openable from the side from which egress is to be made without the use of akey or special knowledge or effort. R311.5 Stairways. R311.5.1 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 ac- cordance with Section R311.5.8. R311.5.2 Headroom. The minimum headroom in all parts of the stairway shall not be less than 6 feet 8 inches (2036 mm) measured vertically from the sloped plane adjoining the tread nosing or from the floor surface of the landing or R311.5.3 Stair treads R311.5.3.1 Riser height. The maximum riser height shall be 73/d inches (196 mm). The riser shall be mea- sured vertically between leading edges of the adjacent treads. The greatest riser height within any flight of stairs shall not exceed the smallest by more than 3/a inch (9.5 mm). R311.5.3.2 Tread depth. The minimu tit tread depot measured horizontally between the vertical planes of the foremost projection of adjacent treads and at aright angle to the tread's leading edge. The greatest tread depth within any flight of stairs shall not exceed the smallest by more than 3/8 inch (9.5 mm). Winder treads shall have a minimum tread depth of 10 inches (254 mm) measured as above at a point 12 inches (305) mm from the side where the treads are narrower. Winder treads shall have a minimum tread depth of 6 inches (152 mm) at any point. Within any flight of stairs, the greatest winder tread depth at the 12 inch (305 mm) walk line shall not exceed the smallest by more than `1/8 inch (9.5 mm). R311.5.3.3 Profile. The radius of curvature at the lead- ing edge of the tread shall be no greater than 9/16 inch 50 (14.3 mm). A nosing not less than 3/q inch (19 mm) but not more than V/., inch (32 mm) shall be provided on stairways with solid risers. The greatest nosing projec- tion shall not exceed the smallest nosing projection by more than 3/8 inch (9.5 mm) between two stories, includ- ing the nosing at the level of floors and landings. Beveling of nosing shall not exceed'/, inch (12.7 mm). Risers shall be vertical or sloped from the underside of the leading edge of the tread above at an angle not more than 30 (0.51 rad) degrees from the vertical. Open risers are permitted, provided that the opening between treads does not permit the passage of 4 -inch diameter (102 mm) sphere. Exceptions: 1. A nosing is not required where the tread depth is a minimum of 11 inches (279 mm). 2. The opening between adjacent treads is not lim- ited on stairs with a total rise of 30 inches (762 mm) or less. R311.5.4 Landings for stairways. There shall be a floor or landing at the top and bottom of each stairway. Exception: A floor or landing is not required at the top of an interior flight of stairs, provided a door does not swing over the stairs. A flight of stairs shall not have a vertical rise greater than 12 feet (3658 mm) between floor levels or landings. The width of each landing shall not be Iess than the stair- way served. Every landing shall have a minimum dimension of 36 inches (914 nun) measured in the direction of travel. R311.5.5 Stairway walking surface. The walking surface of treads and landings of stairways shall be sloped no steeper than one unit vertical in 48 inches horizontal (2 -per- cent slo R311.5.6 Handrails. Handrails shall be provided on at least one side of each continuous run of treads or flight with four r more risers. k RNOMTHeight. Handrail height, measured vertically from the sloped plane adjoining the tread nosing, or fin- ish surface of ramp slope, shall be not less than 34 inches (864 mm) and not more than 38 inches (965 mm). R311.5.6.2 Continuity. Handrails for stairways shall be continuous for the full length of the flight, from a point directly above the top riser of the flight to a point directly above lowest riser of the flight. Handrail ends shall be re- turned or shall terminate in newel posts or safety termi- nals. Handrails adjacent to a wall shall have a space of not less than i'/, inch (38 mm) between the wall and the handrails. Exceptions: 1. Handrails shall be permitted to be interrupted by a newel post at the turn. 2. The use of a volute, turnout, starting easing or starting newel shall be allowed over the lowest tread. 2003 INTERNATIONAL RESIDENTIAL CODE®