When the Ontario Building Code Requires Non-Combustible Construction
Owners usually meet the term non-combustible construction when a consultant tells them their building has to be of it. By then the footprint is often drawn. It is a cheaper conversation to have early.
What the classification means
Non-combustible construction is a defined construction type under Part 3 of the Ontario Building Code. Where it is required, the structural and cladding assemblies must be built from materials meeting a defined non-combustibility standard.
It is a property of the assembly, not a fire resistance rating. A building can be of non-combustible construction and still require applied fire protection on its structural members. The two requirements are separate and both may apply.
What determines whether it is required
Four things, taken together:
- Major occupancy classification. Industrial buildings fall in Group F, subdivided by hazard: F1 high hazard, F2 medium, F3 low. What is stored or processed decides the class, not the shape of the building.
- Building area. Footprint area, which is why the requirement often surfaces when a building grows during design.
- Number of storeys. Including mezzanines where they count as such.
- Street access. How many sides of the building are accessible to firefighting, often the variable owners are least aware of, and it depends on the site plan.
Above the thresholds set for a given combination, non-combustible construction becomes mandatory. Below them, combustible construction may be permitted.
Sprinklers change the arithmetic
Sprinkler protection alters the thresholds in many cases. This means construction type and fire protection strategy should be settled together. Deciding the construction type first and then discovering a sprinkler system was the cheaper route to the same compliance is a common and avoidable sequence.
It runs the other way too. A sprinkler system on a site with limited water supply may need a tank and pump, which is a substantial cost that belongs in the comparison.
Why steel buildings dominate above the thresholds
Steel is non-combustible, so a rigid frame steel building satisfies the classification by construction rather than by treatment. That is the practical reason most Ontario industrial buildings above the combustible thresholds are steel.
The frame is not the whole building, though. The code permits defined combustible elements within non-combustible construction (certain insulations, vapour barriers, roofing components and interior finishes) subject to limits on flame spread rating and smoke developed classification. Foam-core insulated metal panels are a common point of scrutiny. The specific assembly has to be verified against the requirement rather than assumed from the product category.
Spatial separation is a separate constraint
Limiting distance to the property line governs how much unprotected opening an exterior wall may contain and what the wall must be built from. As distance shrinks, permitted openings shrink and the cladding requirement tightens toward non-combustible.
On tight industrial infill sites this frequently determines the footprint, the placement of dock doors and windows, and the wall assembly. Test it before the site plan is fixed.
When to get this settled
At concept, before the footprint is drawn. The determination for any specific building is made by the architect or engineer of record with the authority having jurisdiction, but the questions that drive it are ones an experienced builder can raise at the first meeting.
Getting the classification wrong late means redesigning the envelope, revisiting the fire protection strategy, or moving the building on the site. All three are more expensive than an early conversation.