NBC Standards for Combustible Cladding and Vertical Glazing in Construction

When navigating the complexities of the National Building Code of Canada, partnering with an expert is vital. empcontracting.ca Inc. your construction contractor in London, Ontario, provides the professional oversight needed to ensure compliance with fire safety regulations for noncombustible buildings.

Regulations for Combustible Vertical Glazing

According to Division B of the National Building Code, combustible vertical glazing is subject to specific constraints when installed in buildings required to be of noncombustible construction. These materials are generally permitted up to the second storey, provided they meet strict flame-spread ratings and area limitations.

Flame-Spread Ratings and Area Requirements

Standard combustible glazing must typically maintain a flame-spread rating of not more than 75. However, this may be increased to 150 if the glazing area does not exceed 25% of the wall area of the storey. Specific spacing requirements include:

Ceiling openings must not exceed 25% to 33% of the total ceiling area depending on spacing and assembly size.
Adjacent assemblies must be spaced at least 1.2 m to 2.5 m apart from required fire separations.
In buildings over one storey, glazing must be protected between storeys in accordance with Article 3.2.3.17 unless the building is fully sprinklered.

Combustible Window Sashes and Frames

In noncombustible construction projects, combustible window sashes and frames are permitted. The primary requirement is that they must be vertically non-contiguous between storeys, preventing a continuous path for fire to travel up the building exterior.

Section 3.1.5.5: Combustible Cladding on Exterior Walls

The use of combustible cladding on exterior wall assemblies is permitted in buildings required to be of noncombustible construction under specific conditions defined in Section 3.1.5.5. Generally, the building must be three storeys or less in height or be protected by an automatic sprinkler system.

Fire Testing and Acceptance Criteria (CAN/ULC-S134)

To ensure safety, wall assemblies must be tested according to the CAN/ULC-S134 standard, "Standard Method of Fire Test of Exterior Wall Assemblies." Acceptance depends on two critical fire-performance factors:

Flame Spread: Flaming on or in the wall assembly must not spread more than 5 meters above the opening.
Heat Flux: The heat flux during the flame exposure must not exceed 35 kW/m² when measured at 3.5 meters above the opening.

Fire-Retardant-Treated Wood and Weathering

When an assembly includes combustible cladding made of fire-retardant-treated wood, the material must be subjected to an accelerated weathering test (ASTM D2898) before fire testing. This ensures the fire-retardant properties remain effective despite environmental exposure.

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