Page: Last modified: 2022-10-12
Code Reference(s): NBC20 Div.B 3.4.6.6. (first printing)
Subject: Stairs, Ramps, Handrails and Guards — Fall Protection
Title: Size Limit for Open Stringers
Description: This proposed change limits the size of the triangular openings formed by the stair risers and treads and the bottom element of a required guard.
Related Proposed Change(s): PCF 356
Problem
A size limit for open stringers (the triangular openings formed by the bottom railing of a guard and the risers and treads on the side of a stair) is not clearly addressed in the NBC. The lack of such a provision may lead to the following interpretations:
- open stringers are not regulated by the NBC, or
- open stringers are subject to the same size limits as openings in guards (i.e., not permitting the passage of a spherical object whose diameter is more than 100 mm).
Justification
This proposed change limits the size of the triangular openings formed by the risers and treads of stairs and the bottom element of a required guard.
After reviewing many step dimensions of stairs, the technical committee agreed that:
- limiting the stringer opening to the size of a sphere having a diameter of 150 mm would provide the same performance as that of an elliptical shape measuring 208 mm by 130 mm, and
- using a spherical shape would reduce any enforcement difficulty caused by the use of an elliptical shape.
Furthermore, a 150 mm sphere is the size limit currently used in other codes and standards in other jurisdictions, e.g., Australia.
The technical committee concluded that:
- the size limit for openings in guards (i.e., maximum 100 mm sphere) is too stringent due to the location and shape of open stringers,
- open stringers should limit the passage of a 9- to 11-month-old child, and
- an elliptical shape of 208 mm by 130 mm can be used to represent the torso size of a 9- to 11-month-old child.
PROPOSED CHANGE
[3.4.6.6.] 3.4.6.6.Guards
[1] 1)Every exit shall have a wall or a well-secured guard on each side, where
[a] a)there is a difference in elevation of more than 600 mm between the walking surface and the adjacent surface, or
[b] b)the adjacent surface within 1.2 m of the walking surface has a slope of more than 1 in 2.
(See Note A-9.8.8.1.PROPOSED CHANGE A-9.8.8.1.)
[2] 2)Except as required by Sentence (4), the height of guards for exit stairs and exit ramps as well as their landings shall be not less than 1 070 mm.
[3] 3)The height of guards shall be measured vertically to the top of the guard from
[a] a)a line drawn through the outside edges of the stair nosings, or
[b] b)the surface of the ramp or landing.
[4] 4)The height of guards for exterior stairs and landings more than 10 m above adjacent ground level shall be not less than 1?500 mm measured vertically to the top of the guard from the surface of the landing or from a line drawn through the outside edges of the stair nosings.
[5] 5)Except as provided in Sentence 3.3.1.18.(3) and Articles 3.3.4.7. and 3.3.5.10., guards in exits shall not have any openings that permit the passage of a spherical object whose diameter is more than 100 mm.
[6] –)Except for guards serving industrial occupancies, the triangular openings formed by the risers and treads of a stair and the bottom element of a required guard shall be of a size that prevents the passage of a sphere having a diameter of 150 mm.
[7] 6)In a stairway, a window for which the distance measured vertically between the bottom of the window and a line drawn through the outside edges of the stair nosings is less than 900 mm, or a window that extends to less than 1?070 mm above the landing, shall
[a] a)be protected by a guard that is
[i] i)located approximately 900 mm above a line drawn through the outside edges of the stair nosings, or
[ii] ii)not less than 1?070 mm high measured to the top of the guard from the surface of the landing, or
[b] b)be fixed in position and designed to resist the lateral design loads specified for guards and walls in Articles 4.1.5.14. and 4.1.5.16.
[8] 7)Except for guards conforming to Article 3.3.5.10., guards that protect a level located more than one storey or 4.2 m above the adjacent level shall be designed so that no member, attachment or opening located between 140 mm and 900 mm above the level being protected by the guard facilitates climbing. (See Note A-9.8.8.6.(1)PROPOSED CHANGE A-9.8.8.6.(1).)
Impact analysis
This proposed change, which aims to clarify the intent of the NBC, will have no impact on current installations where the bottom railing of a guard is installed close to the nosing of the tread.
This proposed change has no cost implications and can be achieved by the proper installation of guards (i.e., close to the tread nosing).
Enforcement implications
This change can be enforced by the infrastructure currently available to enforce this Code and may facilitate enforcement.
Who is affected
Designers, manufacturers and building officials.
OBJECTIVE-BASED ANALYSIS OF NEW OR CHANGED PROVISIONS
[3.4.6.6.] 3.4.6.6. ([1] 1) [F30–OS3.1][F10–OS3.7]
[3.4.6.6.] 3.4.6.6. ([2] 2) [F30–OS3.1][F10–OS3.7]
[3.4.6.6.] 3.4.6.6. ([3] 3) no attributions
[3.4.6.6.] 3.4.6.6. ([4] 4) [F30–OS3.1][F10–OS3.7]
[3.4.6.6.] 3.4.6.6. ([5] 5) [F30–OS3.1]
[3.4.6.6.] — ([6] –) [F30–OS3.1]
[3.4.6.6.] 3.4.6.6. ([7] 6) [F30–OS3.1]
[3.4.6.6.] 3.4.6.6. ([8] 7) [F30–OS3.1]
