SDU or MDU: which NBN design does your development need?
Subdivisions, duplexes, townhouses, super lots and apartments each follow different NBN rules. Here is how to tell which applies.
Reviewed 18 October 2026 against NBN-TE-CTO-194 Revision 13.0 and NBN-TE-CTO-284 Revision 16.0
In short: if each dwelling has its own lot fronting a road, it is an SDU and each lot gets a P20 service drop from a pit. If several dwellings sit on one lot, it is an MDU: an apartment building gets a P50 or P100 lead-in and in-building pathways, and townhouses on common property get a small internal pit and conduit network.
Quick guide
| Development | NBN type | What gets designed |
|---|---|---|
| Residential subdivision, stand-alone lots | SDU | Street pits and conduit, one P20 to each lot |
| Duplex or triplex, each dwelling on its own title | SDU | One P20 to each dwelling |
| Townhouses or villas on common property | Horizontal MDU | Internal pits and conduit across common property |
| Super lot with 3 or fewer premises | Super lot | Three individual P20 lead-ins in common property |
| Super lot with 4 to 24 premises | Super lot | Internal P50 pit and conduit network |
| Super lot with 25 or more premises | Super lot | P100 local network with P50 laterals |
| Apartment or mixed-use building, up to 60 premises | Vertical MDU | One P50 lead-in, comms room, risers, pathway to each unit |
| Apartment building, over 60 premises | Vertical MDU | One P100 or two P50 lead-ins, comms room, risers, pathways |
Subdivisions and estates (SDU)
A single dwelling unit is a premises on its own lot. In a subdivision, pits sit in the road verge, P100 and P50 conduits run along and across the streets, and every lot gets its own P20 service drop from a nearby pit, no more than 25 m long. Lots are allocated to a pit in groups of typically four, up to eight. See SDU pit and pipe design.
Duplexes and triplexes
A duplex or triplex is treated as SDU where each dwelling is its own premises: NBN requires one P20 service drop per premises, so two dwellings need two conduits. A common mistake is designing a single shared conduit, which NBN will not accept.
Townhouses and villas (horizontal MDU)
When townhouses share a driveway and common property that a body corporate will own, the pit and pipe sits on private land. NBN treats this as a horizontal MDU. The pits and conduits run across the common property to each dwelling, and at completion the developer grants NBN a licence for exclusive use of the works rather than transferring them.
Super lots
A super lot is a large lot that will later hold several premises. The network inside depends on how many premises it will have, as set out in the table above. Pits and conduits must not go in, or cross, the individual titles inside a super lot.
Apartments and mixed use (vertical MDU)
For a building with dwellings above and beside each other, NBN's MDU standard applies. The design brings a P50 lead-in (or P100 above 60 premises) from the street to the building, and the building needs a communications room of at least 1 m by 1 m, a 500 mm by 500 mm riser space per floor, and a conduit pathway to every unit. See MDU pit and pipe design.
Mixed sites
Some developments mix types, such as a subdivision with a townhouse lot, or a building with ground floor shops. Each part follows its own rules, and commercial premises have their own conduit sizes. Send us the plans and we will confirm how each part is treated before quoting.
SDU or MDU questions
Is a duplex an SDU or an MDU?
Where each dwelling is its own premises on its own title, a duplex is designed like an SDU, with one P20 service drop to each dwelling.
Are townhouses an MDU?
Townhouses on common property owned by a body corporate are a horizontal MDU. Townhouses on separate titles fronting a road are designed like SDUs.
Does the price change between SDU and MDU?
No. NBN Design charges the same per-unit rate for SDU and MDU designs, from $120 per unit.