"Triplex" is a marketing word, not a building code term. Under the National Construction Code (NCC), three homes on one site are either three Class 1a buildings or one Class 2 building. Which one depends on how the homes are arranged, and that decision shapes the whole project.
What Class 1a means
The NCC describes a Class 1a building as a single dwelling. It can be a detached house, or one of a group of two or more attached dwellings, each being a building, separated by a fire-resisting wall. Row houses, terraces, town houses and villa units are given as examples.
The key limit is vertical. A Class 1 building may not sit on top of, or underneath, another dwelling. The same goes for any other class of building, with one exception: a private garage. So three homes side by side, each running from the ground to its own roof and divided by fire-resisting separating walls, can be Class 1a.
What turns a triplex into Class 2
A Class 2 building contains two or more sole-occupancy units, which are separate dwellings in one building. A triplex usually becomes Class 2 when:
- One home sits over another. Even a part of one home, such as a bedroom that extends above a neighbour's living area, breaks the Class 1a rule.
- There is common space below. The ABCB gives dwellings over a shared basement or car park as an example of Class 2.
- The design is a manor house. In the state's Low Rise Housing Diversity (LRHD) Code, a manor house has three or four dwellings with at least one above another, so it falls outside Class 1.
A private garage is treated differently. A garage that belongs to a Class 1 home can sit under or beside it without changing the classification.
Why the classification matters
Class 1a homes are assessed under NCC Volume Two, which relies on the ABCB Housing Provisions for most details. The main extra items for attached homes are the separating walls, which must resist fire and limit sound, and the external wall rules near boundaries.
Class 2 buildings are assessed under NCC Volume One, which brings its own rules for fire safety, accessibility and building services. In NSW, apartment-type buildings also attract extra regulatory obligations for designers and builders. The approval and inspection regime is heavier, and the design cost is usually higher.
Classification also decides who can certify the work. CertifiBuild certifies Class 1 and Class 10 buildings only. A Class 2 triplex must be certified by someone whose registration extends to Class 2.
Planning terms versus building terms
Planning law uses different labels again. Three or more homes on one lot, each with its own ground level access, is generally called multi dwelling housing. Terraces are a type of multi dwelling housing where the homes face a public road and none sits above another. A manor house is a small residential flat building. In most cases, terraces and townhouses line up with Class 1a, while manor houses line up with Class 2, but always check the actual design.
Check the layout early
Where the classification is unclear, the certifier or approval authority decides. Raise it while the scheme is still a concept. A quick review through our plan assessment service can confirm whether a layout stays in Class 1a. See our triplex page for how we help, or our townhouses page for larger rows.
Local help across NSW
CertifiBuild certifies Class 1 and Class 10 work in 39 council areas. Local rules on these council pages are a good place to start: Northern Beaches Council, Wingecarribee Shire Council, Sutherland Shire Council, Fairfield City Council, North Sydney Council, Ku-ring-gai Council.
Suburb pages with local planning notes: Brookvale, Bundanoon, Burraneer, Cabramatta, Cremorne, East Lindfield, Edgecliff, Gordon, Kembla Grange, Kensington. You can also browse every service area.
Sources
- NCC 2022 Volume One Part A6 classification rules, ABCB
- Guide to NCC building classes, ABCB
- Codes SEPP Part 3B, Low Rise Housing Diversity (LRHD) Code page, NSW Planning Portal