BCAB #1942 – Actual and Effective Limiting Distances, and Fire Department Response

November 21, 2024

Re: Actual and Effective Limiting Distances, and Fire Department Response

Project Description

The project is the design and construction of an alteration to a single-family residence to include a secondary suite within the existing space.  The building is not sprinklered and is located in an area where the fire department response time exceeds 10 minutes in 10% or more of the calls.

A new window is proposed in an exposing building face having an actual limiting distance of 1.58 m.

Applicable Code requirements (BCBC 2024)

Sentence 9.10.15.3.(1), Division B, Limiting Distance and Fire Department Response

(1) Except for the purpose of applying Sentences 9.10.15.2.(2), 9.10.15.4.(3) and 9.10.15.5.(13), a limiting distance equal to half the actual limiting distance shall be used as input to the requirements of this Subsection . . .

Sentence 9.10.15.4.(1), Division B, Glazed Openings in Exposing Building Face

(1) Except as provided in Sentences (6) and (7), the maximum aggregate area of glazed openings in an exposing building face shall

(a) conform to Table 9.10.15.4.,

(b) conform to Subsection 3.2.3., or

(c) where the limiting distance is not less than 1.2 m, be equal to or less than the limiting distance squared.

Sentence 3.2.3.1.(8), Division B, Limiting Distance and Area of Unprotected Openings

(8) A limiting distance equal to half the actual limiting distance shall be used as input to Tables 3.2.3.1.-B and 3.2.3.1.-C, where

(a) the time from receipt of notification of a fire by the fire department until the arrival of the first fire department vehicle at the building exceeds 10 min in 10% or more of all fire department calls to the building, and

(b) any storey in the building is not sprinklered.

(See Notes A-3.2.3.1.(8) and A-3.2.3.)

A-3.2.3.1.(8), Division B, Intervention Time and Limiting Distance. (excerpt)

 . . . Where the 10-min limit cannot be met by the fire department at least 90% of the time, Sentence 3.2.3.1.(8) specifies that a value corresponding to half the actual limiting distance be used in requirements that depend on limiting distance to define other criteria . . .

Decision being appealed (Local Authority’s position)

The requirement to halve the limiting distance applies broadly within Subsection 3.2.3., Division B.

The effective limiting distance (0.79 m) would be used in Table 3.2.3.1.-B, Division B, and no interpolation is permitted between the “0” column and the “1.2” column.  However, no unprotected openings are permitted in a wall having an effective limiting distance of 0.79 m.

Appellant's position

The building is a Part 9 building; provisions located in Subsection 3.2.3., Division B, and related to glazed openings have been selected for use, as is permitted.

Provisions in Subsection 3.2.3., Division B, related to related to fire department response time apply exclusively to the use of Tables 3.2.3.1.-B and 3.2.3.1.-C, Division B.  For the purpose of applying Article 3.2.5.1., Division B, the actual limiting distance (1.58 m) is used, not the effective limiting distance (0.79 m).  Therefore, Article 3.2.5.1., Division B, has no application in this situation.

Table 9.10.15.4., Division B, explicitly restricts glazed openings to 0% at any limiting distance less than 1.2 m.  However, Table 3.2.3.1.-B, Division B, restricts unprotected openings to 0% only when the limiting distance is exactly 0 m.  There is no wording in the code that restricts the ability to interpolate between specific columns of Table 3.2.3.1.-B, Division B.  Interpolation is permitted between the first two columns of this table just as it is between any other two columns.

The permitted percentage of unprotected openings can be interpolated from Table 3.2.3.1.-B, Division B, using the effective limiting distance of 0.79 m and the new window is permitted.

Appeal Board Decision #1942

The Board confirms the decision of the local authority. 

It is the determination of the Board that at an effective limiting distance of 0.79 m, no glazed openings are permitted.

Reason for decision

Interpolation between the first two columns in Table 3.2.3.1.-B, Division B, is not permitted, with the effect that no unprotected openings are permitted at a limiting distance below 1.2 m.  This convention in interpreting and applying the Code was established in the 1960’s based on observations of flame fronts emitted from openings during the experimental St. Lawrence burns.

Don Pedde
Chair, Building Code Appeal Board