BCAB #1708 - Roofing Membrane Requirements at Intersection with Wall, Sentence

February 21, 2012

BCAB #1708

Re: Roofing Membrane Requirements at Intersection with Wall, Sentence

Project Description

The project in question is a new single family residence. An exterior stair with a small deck at the top serves an exterior door for the top storey. The wood framed deck has a three inch concrete slab over a single ply modified bituminous roofing membrane. The membrane laps up the wall and under the door threshold. The underside of the door threshold is five inches above the roofing membrane and two inches above the concrete surface creating a three and one quarter inch step between the deck and the interior finished floor.

Reason for Appeal

The small deck meets the conditions described in Sentence to be considered as a roof for the purposes of Section 9.26. Sentence requires built-up roofing to have flashing plies extend not less than 150 mm (6”) up an intersecting wall behind the wall sheathing paper. Although the roofing in question is not “built-up” the requirements are typically applied to all types of membrane roofing. There is also an allowance in Sentence for a maximum six inch step at an exterior door from a dwelling unit where there is potential for it to be blocked by ice or snow.

Appellant's Position

The appellant contends that it isn’t possible to simultaneously conform to both Sentences and at the doorway. The allowance in Sentence for a maximum 150 mm step implies a lesser step is acceptable.  As the Code does not appear to establish a minimum step at an exterior door there should be an exemption for the 150 mm flashing under the door threshold.

Building Official's Position

The building official maintains the requirements for built-up roofing to lap up the intersecting wall for 150 mm is applicable to single membrane roofing and there is no relaxation to reduce the lap at a doorway.

Appeal Board Decision #1708

It is the determination of the Board that Article does not apply to single ply membrane sheet roofing so the requirement for 150 mm of flashing plies on the wall is not applicable. Even where the Code does require roofing to lap up an intersecting wall a specified dimension this would not apply below a door.

George Humphrey, Chair