Fire design is one of the biggest reasons commercial buildings change shape between first sketch and consent. Put a warehouse close to a boundary and the wall facing it may need to be fire-rated, with few or no openings. Knowing the basics early saves redesigns and money.
The rules in one paragraph #
The Building Code’s fire clauses (C1 to C6) set what every building must achieve. For most buildings other than houses, the usual way to show compliance is the Acceptable Solution C/AS2, currently the 2nd edition, in force since 28 July 2025. Complex or unusual buildings may instead use the Verification Method C/VM2, which needs a chartered fire engineer and specialist modelling.
Five ideas that drive the design #
1. The relevant boundary. Fire rules care about how far each wall is from the boundary it faces. The closer the wall, the stricter the rules, because fire can spread to the neighbour’s property.
2. Two buildings on one site. If you’re adding a second building on your own land, the rules draw an imaginary “notional boundary” halfway between them. A new shed 3 m from your existing garage is treated as being 1.5 m from a boundary.
3. Unprotected area. Doors, windows, skylights and ordinary cladding count as unprotected area, because fire can pass through them. Close to a boundary, only a small share of a wall can be unprotected. The triangle of a gable end above the wall counts too, which is easy to forget.
4. Fire resistance rating (FRR). A fire-rated wall is shown as three numbers, such as -/60/60: minutes of structural adequacy, integrity and insulation. Rated walls are built with tested systems, usually specific linings fixed to the frame.
5. Getting people out. Escape routes, exit distances, door widths and signage depend on how many people use the building and what’s stored in it. Larger or higher-risk buildings may need alarms or sprinklers.
What storage does to fire design #
What you store, and how high you stack it, changes the fire load and the rules. Hand-stacked boxes and high-rack pallet storage are treated very differently. Tell your designer the real use from day one.
Practical ways to keep fire costs down #
- Move the building. A few extra metres from the boundary can remove the need for a rated wall.
- Put doors where it’s easy. Roller doors and windows go on walls facing away from boundaries.
- Plan the whole site. Think about where future buildings might go, so today’s shed doesn’t force tomorrow’s into a rated wall.
Steel and fire #
Steel doesn’t burn, which is a real advantage for stored goods and insurance conversations. But unprotected steel does lose strength at high temperatures, so where the rules call for a rating, it comes from the tested wall or lining system, not the steel alone.
How Steelspan handles it #
We work with specialist fire engineers on fire reports for consent, including PCD of Hamilton, who work countrywide, and CoveKinloch. We install passive fire protection and linings in-house, so the rated walls on the drawings are the rated walls on site.
Commercial land is valuable, so many owners want to build as close to the boundary as they can. We’ll guide you through the options and what each costs, such as a GIB fire-rated wall or a concrete tilt panel wall. The ground matters too: if the geotechnical report shows the soil can’t support heavy concrete panels or block walls on the boundary, a lighter fire-rated system may be the answer.
Talk to Steelspan #
Send us your site plan early, and we’ll show you where a building can go with the fewest fire constraints. Use our Easy Shed Quote or call 0800 787 726.
