Triplex certification in NSW

Which planning type fits my design?

Multi dwelling housing means three or more homes, attached or detached, on one lot. Each home must have its own ground level access. It does not include an apartment building. Three homes in a row, an L-shape or a front and rear layout can all fit.

Terraces are a narrower type. All the homes must be attached. They must face, and generally line up along, one or more public roads.

A manor house is a building no higher than two storeys containing three or more homes, with at least one home wholly or partly above another. That stacking means it is not a Class 1 building, so we cannot certify it.

Is a DA required?

Under the state rules, terraces qualify for a CDC (granted by a private certifier against set standards) only in zones RU5, R1, R2 or R3, and only where council already permits multi dwelling housing. Council's minimum lot size applies, or 600 square metres where council has no figure. Three homes that do not all front the street do not count as terraces, and they usually need a development application (DA) to council.

Since 28 February 2025, multi dwelling housing is also allowed in the R2 zone near nominated stations and town centres. That route needs a DA. The NSW Housing Pattern Book, launched in July 2025, offers a faster pathway for pre-designed terraces, townhouses and manor houses. Manor house designs are still outside our scope.

What about the walls between the homes?

In a row of three, the middle home has a separating wall on each side. Every pipe, cable or duct through these walls must keep the wall's fire rating. The building code sets a -/60/60 rating at openings, with limits on cable size and packing around each cable.

Switches and power outlets need care. Unless a tested system is used, an outlet in a separating wall must either sit at least 300 mm horizontally and 600 mm vertically from an outlet on the other side, or be no deeper than half the wall thickness. Any gap around it must be packed with fire-resisting material. In hollow walls, the cavity behind the outlet must be framed and packed too.

How much sound must the walls block?

The separating walls must also limit airborne and impact sound. The standard wall systems have a sound rating (Rw + Ctr) of at least 50. A water pipe serving one home must not be fixed to the neighbour's side of the wall. It needs at least 10 mm clearance from it.

These details are easy to miss once plasterboard goes up. Get them checked on site before the walls are closed in.

Garages built against a neighbour's home

In a row of three, a garage can end up against the neighbouring home instead of the home it serves. The NCC (National Construction Code) treats that wall as a separating wall as well. Its separating wall rules reach walls between two Class 1 dwellings and also walls between a Class 1 dwelling and a Class 10a building, such as a garage, that belongs to some other home.

So a garage serving home A that adjoins home B needs the same fire rated wall as two living areas side by side. That means a fire resistance level (FRL) of 60/60/60, or masonry of 90 mm or more, starting at the footings or slab. The explanatory note in the code says the sound insulation rules for separating walls take the same scope.

Check garage positions on the floor plans before the development application (DA) is lodged. Flipping a garage from one side of a home to the other late in design can create a separating wall that nobody has detailed.

Where brick veneer meets a separating wall

Many triplexes are clad in masonry veneer. At both ends of each separating wall, the veneer outer skin meets the fire rated wall, and that junction needs its own detail.

The code caps any gap between the separating wall and the veneer at 50 mm. That gap has to be filled with fire-resisting material, arranged so the outside wall still keeps out the weather as the code requires. With two separating walls, a triplex has at least four of these junctions, one at the front and one at the back of each wall.

Show the junction on the drawings as a detail, not a note. On site, keep it open for inspection before the gap is sealed and the veneer is finished around it.

Smoke alarms in each of the three homes

Each home in a triplex is a separate Class 1a dwelling with its own smoke alarms. Each alarm must be an AS 3786 product, wired to the home's mains electricity where the building is connected.

Inside each home, the code calls for an alarm on any storey with bedrooms, in every corridor or hallway linked to a bedroom, and on each storey without bedrooms. Where one home contains several alarms, they are linked, so smoke at one sets off all of them.

That link stops at the home's own walls. The code's explanatory note says alarms in one Class 1a dwelling need not connect to alarms next door. Lay out three separate alarm circuits on the electrical plans, one per home, so each can be tested and signed off on its own.

Building the three homes to sell

Many triplexes are built so one or more homes can be sold. In NSW, a building business must hold home building compensation (HBC) cover once a home building project is worth more than $20,000, GST included. It applies to new homes and to new apartment buildings of up to 3 storeys.

The business must hand the certificate of HBC cover to the developer, homeowner or owner-builder before work starts or any payment is taken, deposits included. A builder developing its own land, often called a spec builder, must buy the cover too, and the certificate has to go into any contract of sale.

Subcontractors do not need their own policy, since the building business carries the cover for the work. Check the insurance certificate describes the same homes and address as the approved plans before the first inspection is booked.