BCAB #1700 - Support of Fire Rated Exterior Wall, Subsections 3.2.2. & 3.2.3.
October 20, 2011
Re: Support of Fire Rated Exterior Wall, Subsections 3.2.2. & 3.2.3.
The building in question is an unsprinklered single storey structure with tilt-up concrete walls and a steel roof structure that is not required to have a fire resistance rating under Subsection 3.2.2. It is intended for Group A Division 2 or Group E major occupancy and has a building area of 235 square metres. The north exposing building face is required to have a 2 hour fire resistance rating in conformance with Subsection 3.2.3.
Reason for Appeal
Although fire rated exterior walls are not specifically addressed there are Code requirements requiring other fire rated assemblies to be supported by structural components with the same fire resistance rating. The intent is that the fire rated assembly will not fail prematurely because what supports it has a lower fire resistance rating. The exterior walls of many tilt-up concrete buildings, this one included, rely on the roof structure to for their structural stability.
The appellant contends that although the Code has provisions regarding the need for supporting floors with a fire resistance rating with structures with at least an equal fire resistance rating (3.2.2.) there are no such provisions for exposing building faces. A specific provision for such fire rated support existed in the 1992 BC Building Code but was not carried into the 1998 BC Code, is not in the current 2006 edition and has never been in the model National Building Code on which the BCBC is based. As there appears to be no requirement, either explicit or implicit, to require a fire resistance rating for the laterally supporting roof, it is the appellant’s contention it is not required to rate the roof of an unsprinklered building with tilt-up concrete walls requiring a fire resistance rating for spatial separation reasons.
Building Official's Position
The building official maintains there is an implicit provision to support the fire rated exterior wall based on the definition of fire resistance rating in the Building Code and in the test standard, ULC-S101, “Standard Methods of Fire Endurance Tests of Building Construction and Materials.” Both the definition and the test require an assembly to withstand the passage of flame and transmission of heat for a specified time. If failure of the assembly occurs before the required time has elapsed the fire resistance rating is not met. Previous appeals #907 and #907A from 1987 and 1988 respectively support this position and pre-date the inclusion of specific tilt-up wall provisions in the 1992 BC Building Code.
Appeal Board Decision #1700
Fire resistance ratings required by the Code are determined by a specified test process for individual wall, floor or roof assemblies. The test does not account for the interaction between individual assemblies and the Code does not provide specific provisions requiring an exposing building face to be supported by construction with an equivalent fire resistance rating. Therefore, it is the determination of the Board that the roof structure is not required to have a fire resistance rating for the purpose of supporting the exposing building face for the duration of its fire resistance rating.
Edward Mackinnon, Vice Chair