Ministry of Municipal Affairs
PROPOSED CHANGE TO THE 2012 BUILDING CODE
O. REG. 332/12 AS AMENDED
CHANGE NUMBER:
B-03-03-07
SOURCE:
Ontario-NBC
CODE REFERENCE:
Division B / 3.3.1.15.
DESCRIPTION OF THE PROPOSED AMENDMENT
This proposed change, along with the changes to Article 9.8.4.3. in Part 9, introduces consistent terminology and
states the proper way of constructing tapered treads in other than required exit stairs in Part 3 and Part 9 buildings.
EXISTING 2012 BUILDING CODE PROVISION(S)
3.3.1.15. Curved or Spiral Stairs
(1) A curved or spiral stair is permitted in a stairway not required as an exit provided the stair has,
(a) treads with,
(i) a minimum run not less than 150 mm, and
(ii) an average run not less than 200 mm, and
(b) risers in conformance with Sentence 3.4.6.8.(2).
PROPOSED CODE CHANGE
Revise Article 3.3.1.15 as follows:
3.3.1.15. Curved or Spiral Stairs Tapered Treads in a Curved Flight
(1) A curved or spiral stair is permitted in a stairway not required as an exit provided the stair has,Flights of stairs shall
consist solely of
(a) treads with,straight flights, or
(i) a minimum run not less than 150 mm, and
(ii) an average run not less than 200 mm, and
(b) risers in conformance with Sentence 3.4.6.8.(2).curved flights that comply with Sentence (2)
(2) Tapered treads in a curved flight that is not required as an exit shall have
(a) a minimum run of 150 mm
(b) a minimum run not less than of 280 mm measured at 300 mm from the center line of the handrail at the narrow end
of the tread, and
(c) a riser in conformance with Sentence 3.4.6.8.(2)
(3) Tapered treads shall have a consistent angle and uniform run and rise dimensions in accordance with the
construction tolerances stipulated in Article 3.4.6.8. when measured at a point of 300 mm from the center line of the
handrail at the narrow end of the tread.
Building and Development Branch
© Copyright Queen’s Printer for Ontario 2016
Page 1
(4) All tapered treads within a flight shall turn in the same direction.
RATIONALE FOR CHANGE
Problem/General Background
Inconsistency of Terminology
The current use of various terms to describe non-rectangular treads is ambiguous, confusing and not aligned with
the current practices in other international codes.
1.
Part 3, Article 3.3.1.15. refers to curved or spiral stair while Part 9, Article 9.8.4.3. talks about angled
tread, to designate curved stairs in other than exit stairs;
2.
The terms curved stair and tapered treads are used to refer to the circular stair, required if used in exit
stair, stated in Article 3.4.6.9. for both Part 3 and Part 9 buildings;
3.
The term "winder" in Article 9.8.4.5. is used to designate treads that converge to a point allowed only
inside dwelling units under certain conditions;
4.
Finally, terms such as curved flight and curved run are also used to describe stair configurations in Article
9.8.3.1.Sentence (1).
Technical problems
•
Part 3 does not have a provision that clearly states the permitted stair configurations for Part 3 buildings,
similar to what is provided in Article 9.8.3.1. for public stairs, Part 9 .
•
Tapered tread construction requirements in Articles 3.3.1.16. and 9.8.4.3. are not aligned with the
minimum requirements in international codes and are not consistent with the current Part 3 requirements
for rectangular tread dimensions in public stairs.
Justification/Explanation
This proposed change would harmonize requirements with the model National Building Code of Canada.
Inconsistency in Used Terminology
The proposed change would:
1.
Use the term “tapered treads” in curved flight in exit stairs and in other than exit stairs.
2.
Use the term “curved flight” when made of tapered treads.
Technical Changes
The proposed changes to Article 3.3.1.15 and to Article 9.8.4.3. in Part 9 states minimum dimensions and
describes an acceptable method of constructing tapered treads in public stairs, to improve safety and stair usability
and to achieve consistency and reasonably safe stair layouts.
Building and Development Branch
© Copyright Queen’s Printer for Ontario 2016
Page 2
This construction method follows the recommendation made by the Council of American Building Officers,
Board for Coordination of the Model Codes (CABO/BCMC) in its report on General Building Requirements
published in 1985 and is consistent with the current requirements in the U.S Model Building Codes and NFPA
101. This construction method is also consistent with the minimum run dimension of rectangular treads for Part 3
public stairs.
Sentence (1)
The proposed change clarifies that only straight flights or curved flights are allowed in Part 3 public stairs.
Sentences (2)
The proposed Change maintains a minimum tread run dimensions of 150 mm along the narrow end of treads and
requires a minimum run of 280 mm along what is recognized as a travel line at 300 mm away from the handrail at
the narrow end of the tread. The measurement is made to the center line of the handrails because handrails usually
dictate users’ location in the curved flight and the 280 mm is consistent with the minimum run dimension for
rectangular tread.
Sentence (3)
The measurement of two elements will result in all tapered treads having uniform angle and shape. A consistent
angle and a uniform run dimensions would achieve a reasonable uniformity of tapered treads. This assures that
whatever the travel line a person uses when walking on the tapered treads leads to the feet landing on consistently
sized treads, keeping in mind that, depending on one’s gait, one foot will consistently encounter tread runs either a
bit smaller or a bit larger than the other foot does.
Sentence (4)
Move the part of the deleted sentence 3.4.6.8.(6) that deals with the direction of the turn to new Sentence
3.3.1.15.(4).
Cost/Benefit Implications
Tapered treads in public stairs, if constructed to the new rules would slightly increase the amount of floor area
devoted to the stair and the cost associated to it, in comparison to the actual requirements in the Building Code.
The benefit of having safer treads would however reduce the probability of missteps and falls in stairs and
therefore reduce injuries and heath related cost.
Enforcement Implications
The changes can be enforced by the available infrastructure without an increase in resources and can facilitate
enforcement and determination of compliance.
Who is Affected
Designers, builders and building officials.
Building and Development Branch
© Copyright Queen’s Printer for Ontario 2016
Page 3
Objective Based Analysis
Provision
Objective/Functional Statement
Division B 3.3.1.15.
(1)
[F30-OS3.1][F10-OS3.7]
(2)
[F30-OS3.1][F10-OS3.7]
(3)
[F30-OS3.1][F10-OS3.7]
(4)
[F30-OS3.1][F10-OS3.7]
OTHER SUPPORTING MATERIALS
Building and Development Branch
© Copyright Queen’s Printer for Ontario 2016
Page 4