BCAB #1602 - Clearance to Combustible Construction, Sentence 9.21.5.1.(1) Height of Chimney Flues, Sentence 9.21.4.4.(1)

November 10, 2004

BCAB #1602

Re: Clearance to Combustible Construction,  Sentence 9.21.5.1.(1) Height of Chimney Flues, Sentence 9.21.4.4.(1)

Project Description

A chimney of masonry construction extends above the roofline. A combustible torch-on roofing membrane extends over the metal chimney flashing and up the masonry chimney to the chimney cap.

Reason for Appeal

Sentence 9.21.5.1.(1) requires the clearance between a masonry chimney and combustible framing to be not less than 50 mm for interior chimneys and 12 mm for exterior chimneys.

Sentence 9.21.4.4.(1) requires a chimney flue to extend not less than 900 mm above the highest point at which the chimney comes in contact with the roof.

Appellant’s Position

The appellant contends the combustible waterproof roofing membrane is permitted to extend up the masonry chimney exposed to the exterior. The appellant does not consider the roofing membrane to be “combustible framing.”

Building Official's Position

The Building Official considers it inconceivable that a combustible roofing membrane be permitted to span the clearances required by the Code and extend up the outside of the chimney to the edge of the flue opening. The Building Official considers the required height of the chimney, 900 mm above the roof, should be measured from the roofing membrane.

Appeal Board Decision #1602

Sentence 2.4.1.1.(1) requires all materials and systems to “possess the necessary characteristics to perform their intended functions when installed in a building.” The intent of Sentence 9.21.5.1.(1) is to reduce the probability that excessive heat transfer by conduction or radiation from a masonry or concrete chimneys (especially during chimney fires) will lead to ignition of combustible components, which could lead to the harm of persons.

It is the determination of the Board that the location of the combustible roofing membrane on the chimney makes it susceptible to ignition which could compromise the safety of persons and thus does not comply with the requirement of Sentence 2.4.1.1.(1).

George Humphrey, Chair