Staff Analysis for
Declaratory Statement Request DS-2013-001
March 21, 2013
Issue: DS-2013-001. The Petitioner, Ken Rich, seeks a Declaratory Statement on R311of the
Florida Building Code, Residential.
Petitioner in DS-2013-001 seeks clarification of the following questions:
Question 1: Since the stair design as shown in Diagram A, meets the guidelines of the Florida Building Code Sections R311.7.1 through R311.7.8 is it also required, in addition, to meet Florida Building Code, Residential, Section R311.9.3* of which, by definition, it is not.
*(Note that the original language of DS-2013-001 mistakenly referenced Section R311.9.3, which does not exist.)
Ken Rich, representing Weber Design Group, seeks clarification of code requirements regarding a residential circular stair design as indicated in the attached “Diagram A”.
It should be noted that the charge of staff was not to analyze the proposed stair design for code compliance, but rather assess the applicability of relevant code sections.
Florida Building Code, Residential Section R311.7.1 through R322.214.171.124
The Proponent is questioning the application of Section R3126.96.36.199 to the proposed stair design since he claims that the design is in compliance with all other code requirements indicated in Sections R311.1-R311.8. Sections R311.1-R311.8 address stair design criteria, including winder treads, whereas Section R3188.8.131.52 specifically addresses tread depth and stair radius. Section R3184.108.40.206 was added as a supplement to the 2009 IRC base code as a Florida specific requirement to the 2010 FBC.
Relevant Code Sections
Section R202 Definitions
CIRCULAR STAIRS. A stairway with steps that result in a sweeping circular or curved pattern, but not spiral stairs.
WINDER. A tread with nonparallel edges.
Section R311.7 Stairways
R311.7.1 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 311/2 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 R3220.127.116.11.
R311.7.2 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 line adjoining the tread nosing or from the floor surface of the landing or platform on that portion of the stairway.
Exception: Where the nosings of treads at the side of a flight extend under the edge of a floor opening through which the stair passes, the floor opening shall be allowed to project horizontally into the required headroom a maximum of 43/4 inches (121 mm).
R311.7.3 Walkline. The walkline across winder treads shall be concentric to the curved direction of travel through the turn and located 12 inches (305 mm) from the side where the winders are narrower. The 12-inch (305 mm) dimension shall be measured from the widest point of the clear stair width at the walking surface of the winder. If winders are adjacent within the flight, the point of the widest clear stair width of the adjacent winders shall be used.
R311.7.4 Stair treads and risers. Stair treads and risers shall meet the requirements of this section. For the purposes of this section all dimensions and dimensioned surfaces shall be exclusive of carpets, rugs or runners.
R318.104.22.168 Riser height. The maximum riser height shall be 7 3/4 inches (196 mm). The riser shall be measured 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 3/8 inch (9.5 mm).
R322.214.171.124 Tread depth. The minimum tread depth shall be 10 inches (254 mm). 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 greatest tread depth within any flight of stairs shall not exceed the smallest by more than 3/8 inch (9.5 mm). Consistently shaped winders at the walkline shall be allowed within the same flight of stairs as rectangular treads and do not have to be within 3/8 inch (9.5 mm) of the rectangular tread depth.
Winder treads shall have a minimum tread depth of 10 inches (254 mm) measured between the vertical planes of the foremost projection of adjacent treads at the intersections with the walkline. Winder treads shall have a minimum tread depth of 6 inches (152 mm) at any point within the clear width of the stair. Within any flight of stairs, the largest winder tread depth at the walkline shall not exceed the smallest winder tread by more than 3/8 inch (9.5 mm).
R3126.96.36.199 Profile. The radius of curvature at the leading edge of the tread shall be no greater than 9/16 inch (14.3 mm). A nosing not less than 3/4 inch (19 mm) but not more than 11/4 inches (32 mm) shall be provided on stairways with solid risers. The greatest nosing projection shall not exceed the smallest nosing projection by more than 3/8 inch (9.5 mm) between two stories, including the nosing at the level of floors and landings. Beveling of nosings shall not exceed 1/2 inch (12.7 mm). Risers shall be vertical or sloped from the underside of the leading edge of the tread at an angle not more than 30 degrees (0.51 rad) from the vertical. Open risers are permitted, provided that the opening between treads does not permit the passage of a 4-inch (102 mm) diameter sphere.
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 limited on stairs with a total rise of 30 inches (762 mm) or less.
R3188.8.131.52 Exterior wood/plastic composite stair treads. Wood/plastic composite stair treads shall comply with the provisions of Section R317.4.
R311.7.5 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, including stairs in an enclosed garage, provided a door does not swing over the stairs. A flight of stairs shall not have a vertical rise larger than 12 feet (3658 mm) between floor levels or landings. The width of each landing shall not be less than the width of the stairway served. Every landing shall have a minimum dimension of 36 inches (914 mm) measured in the direction of travel.
R311.7.6 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-percent slope).
R311.7.7 Handrails. Handrails shall be provided on at least one side of each continuous run of treads or flight with four or more risers.
R3184.108.40.206 Height. Handrail height, measured vertically from the sloped plane adjoining the tread nosing, or finish surface of ramp slope, shall be not less than 34 inches (864 mm) and not more than 38 inches (965 mm).
1. The use of a volute, turnout or starting easing shall be allowed over the lowest tread.
2. When handrail fittings or bendings are used to provide continuous transition between flights, the transition from handrail to guardrail, or used at the start of a flight, the handrail height at the fittings or bendings shall be permitted to exceed the maximum height.
R3220.127.116.11 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 the lowest riser of the flight. Handrail ends shall be returned or shall terminate in newel posts or safety terminals. Handrails adjacent to a wall shall have a space of not less than 11/2 inch (38 mm) between the wall and the handrails.
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.
R318.104.22.168 Grip-size. All required handrails shall be of one of the following types or provide equivalent graspability.
1. Type I. Handrails with a circular cross section shall have an outside diameter of at least 11/4 inches (32 mm) and not greater than 2 inches (51 mm). If the handrail is not circular, it shall have a perimeter dimension of at least 4 inches (102 mm) and not greater than 61/4 inches (160 mm) with a maximum cross section of dimension of 2 1/4 inches (57 mm). Edges shall have a minimum radius of 0.01 inch (0.25 mm).
2. Type II. Handrails with a perimeter greater than 61/4 inches (160 mm) shall have a graspable finger recess area on both sides of the profile. The finger recess shall begin within a distance of 3/4 inch (19 mm) measured vertically from the tallest portion of the profile and achieve a depth of at least 5/16 inch (8 mm) within 7/8 inch (22 mm) below the widest portion of the profile. This required depth shall continue for at least 3/8 inch (10 mm) to a level that is not less than 13/4 inches (45 mm) below the tallest portion of the profile. The minimum width of the handrail above the recess shall be 11/4 inches (32 mm) to a maximum of 23/4 inches (70 mm). Edges shall have a minimum radius of 0.01 inch (0.25 mm).
R322.214.171.124 Exterior wood/plastic composite handrails.Wood/plastic composite handrails shall comply with the provisions of Section R317.4.
R311.7.8 Illumination. All stairs shall be provided with illumination in accordance with Section R303.6.
R311.7.9 Special Stairways
R3126.96.36.199 Circular stairways. Circular stairs may have a minimum tread depth of 9 inches (229 mm) with 1 inch (25.4 mm) of nosing, and the smaller radius may be less than twice the width of the stairway.
As far as the requirement of the proposed design to meet the currently adopted FBC Section R3188.8.131.52, the answer to the Question should be YES since it deals with Circular Stairways, and the proposed design indicated in Diagram “A” of the DEC Statement meets the definition of Circular Stairs as indicated in Section R202.
R3184.108.40.206 addresses the minimum radius of the stair, which is not addressed elsewhere in the code, which in itself indicates the need for compliance with this section. It should be noted that the requirements of R3220.127.116.11 can be viewed as duplicating the minimum tread depth requirements of winder treads of Section R318.104.22.168, however R322.214.171.124 is very specific in prescribing minimum and maximum tread depths and clearly describes the method of measurement of the tread depth. The text of R3126.96.36.199 reiterates the minimum tread depth requirement indicated in R3188.8.131.52 (9” tread +1” nosing = 10”). Since R3184.108.40.206 does not indicate a specific method of tread depth measurement, it should be assumed that the correct method of tread depth measurement is as described in R3220.127.116.11, which does not specifically address nosings in the measurement – only “foremost projections”.
The fact that a winder tread is a component of a circular stair, Staff recommends that the TAC review the language of Section R318.104.22.168 to assess the clarity of what the Section is requiring for tread depth, since it may be viewed as either conflicting with or duplicative of Section R322.214.171.124. Staff would also recommend TAC review and clarification of the minimum radius component of Section R3126.96.36.199. If the TAC finds that the language of Section R3188.8.131.52 is in conflict with or duplicates other sections, the answer to the Question should be NO.
It should also be noted that the proposed design in Diagram “A” incorporates both parallel and non-parallel treads as mentioned by the Petitioner is irrelevant in determining the required depth of a winder tread.
Staff Recommendations: Based on the above facts and circumstances, staff provides the following recommendations as answers to proponent’s question:
To the question : “Since the stair design as shown in Diagram A, meets the guidelines of the Florida Building Code Sections R311.7.1 through R311.7.8, is it also required, in addition, to meet Florida Building Code, Residential, Section R3184.108.40.206 of which, by definition, it is not.”
The question can be answered from two different perspectives:
Option 1. With the assumption that the proposed design meets the requirements of Sections R311.7.1through R3220.127.116.11, of the 2010 FBC, Residential, the answer to Question 1 should be YES since it deals with Circular Stairways, and the proposed design meets the definition of Circular Stairs as indicated in Section R202.
Option 2. With the assumption that the proposed design meets the requirements of Sections R311.7.1through R318.104.22.168 of the 2010 FBC, Residential, and the language in Section R311.7.9.is determined to be duplicative to that of Section R322.214.171.124, the answer to the Question should be NO.