Class 1B vs Class 1a.
The difference between the two building classifications under the National Construction Code — and why it matters for a co-living or rooming house development.
What is Class 1a?
Class 1a is the classification for a single dwelling — a detached house, or one of a group of attached dwellings, each occupied by a single household. It is the classification that applies to a standard residential home.
What is Class 1B?
Class 1B is the classification for a boarding house, guest house or hostel of a limited scale — a building where multiple unrelated people live and share facilities. It is the classification most commonly applied to rooming houses and small co-living developments.
Why the difference matters
The classification is not a technicality. It changes the fire safety, egress, room-size, sanitary-facility and accessibility requirements of the building, and therefore the design, the specification and the cost. A development designed as a standard Class 1a dwelling and then used as a rooming house can be non-compliant — and that is a risk to the investment.
Class 1a vs Class 1b at a glance.
| Aspect | Class 1a | Class 1b |
|---|---|---|
| Use | Single dwelling | Boarding/guest house or hostel (limited scale) |
| Occupants | One household | Multiple unrelated people |
| Fire safety | Residential provisions | Enhanced for scale |
| Egress | Standard | Sized for occupant count |
| Sanitary facilities | To suit one household | Ratio for occupants |
| Accessibility | Limited | Accessible provisions required |
| Typical application | Standard house | Rooming house / co-living |
Class 1B vs Class 1a FAQs.
What is the difference between Class 1a and Class 1b?
Class 1a covers a single dwelling for one household. Class 1b covers boarding houses, guest houses and hostels of a limited scale where multiple unrelated people live and share facilities. Class 1b carries enhanced fire safety, egress, sanitary-facility and accessibility provisions.
Can a Class 1a house be used as a rooming house?
Using a building as a rooming house when it was designed and approved as a Class 1a dwelling can be non-compliant, because the fire safety, egress and facility provisions differ. The classification should match the intended use from the outset.
How do I know which classification applies?
The correct classification depends on the use, scale and configuration of the building. It should be confirmed with a building surveyor early in the design process, because it shapes the requirements the building has to satisfy.
Get the classification right early.
The classification shapes the design, the cost and the compliance. Assess your site and the classification that applies.
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