Pit and pipe design for single dwelling unit developments
NBN requires a dedicated lead-in conduit from an NBN pit to each premises. We design the pits, routes and conduit sizes for your subdivision, duplex or triplex and prepare the design for NBN review.
Reviewed 14 October 2026 against NBN-TE-CTO-194 Revision 13.0
In short: an SDU pit and pipe design shows where every NBN pit goes, how the conduits run along the street and across roads, and the P20 service drop conduit that runs from a pit to each lot. NBN reviews it through the New Developments portal before you build. We prepare it to NBN's current standard, priced per lot from $120, and turn it around within two weeks of receiving complete CAD plans.
What counts as an SDU
A single dwelling unit is a premises on its own lot: a house in an estate, a stand-alone lot in a subdivision, or each dwelling in a duplex or triplex where every dwelling has its own title. NBN treats each of these as a separate premises that needs its own conduit. If several dwellings share one lot and common property, the site is usually an MDU or a super lot instead. Our guide to SDU or MDU explains how to tell which applies.
What the design covers
- Pit locations and pit types, using only the pits NBN's standard allows
- Distribution and local network conduit routes along the street, sized P100 or P50 as the standard requires
- Road crossings and lateral conduits between pits on opposite sides of the road
- One P20 service drop conduit from a pit to each lot, with its length and entry position
- Existing roads, kerbs, driveways, poles, transformers and telecommunications pits around the site
- Lot numbers and a premises count that matches your stage application
- A design set ready to upload to the nbn New Developments portal
See what's in a design package for the full list of drawings and schedules you receive.
Rules that shape an SDU design
These come from NBN's pit and conduit standard, NBN-TE-CTO-194. They drive most of the decisions on a residential layout.
One P20 service drop conduit per premises, including each dwelling in a duplex or triplex.
The furthest service drop run from a pit to the property boundary entry must not exceed 25 m.
Service drops start 1 m inside the lot with an end cap, and are labelled in the pit with the lot, left or right position and distance from the boundary.
Minimum cover over a service drop is 300 mm where the run from pit to boundary is under 3 m, and 450 mm where it is longer.
Total bends between two pits cannot exceed 180 degrees, and sharp 90 degree elbows are not allowed.
Pits sit at least 15 m from pad-mounted transformers and transformer poles, at least 3 m from other poles, and where practical 1 m from the back of kerb.
Where practical, the long side of a pit is offset 350 mm from the street-facing boundary and kept clear of driveways and proposed driveways.
Designs most often come back from review on one of these points: a service drop that runs too far, a pit that lands on a future driveway, or a pit too close to a transformer. We check each one before the design goes to NBN.
One pit, several lots
NBN's standard allocates lots to a service drop or boundary pit in groups of typically four, up to a maximum of eight. Each lot still gets its own P20 conduit from that pit, so every premises has a dedicated path. How many conduits a pit can take also depends on its size: NBN publishes a table of the maximum conduit combinations at each end of every pit type. Our pits and conduit guide sets that table out in plain terms.
Staged subdivisions
Most estates are released in stages. We design each stage so its conduit network ties into the previous stage and leaves a clean connection point for the next. If you already have an approved design for an earlier stage, send it with your plans and we will match pit numbering, conduit sizes and tie-in points.
Retaining walls, laneways and corner lots
A few site features change the layout. Where a service drop has to pass under a retaining wall, the P20 conduit must go in before the wall is built. Laneway lots have their own conduit rules, and where conduit changes size into a street crossing or around a corner, the pit sits between 3 m and 15 m from the adjacent property corner. Tell us about any of these when you send plans and we will design around them.
What we need to start
- Site address and state or territory
- Number of lots and the stage of the development
- CAD (DWG) development plans showing roads, lot boundaries, kerbs and existing services (PDF is fine for small sites)
- Your NBN application reference, if you have one
- Dial Before You Dig or site survey results, if you have them
Good CAD saves the most time. Our guide to preparing CAD plans lists what to include.
Small developments
For small developments of up to 20 premises, NBN accepts designs as PDF files, and using NBN's AutoCAD drafting tool is optional. Small jobs still need the same pit, conduit and clearance rules applied, and are priced the same way as larger ones, from $120 per lot with no minimum fee.
Price
From $120 per lot, with lower rates as the project grows: a 10 lot subdivision is $1,200 and a 30 lot stage is $3,295. See the price guide and calculator.
SDU design questions
Does a duplex need two conduits?
Yes. NBN requires one P20 service drop conduit per premises, so each dwelling in a duplex or triplex gets its own conduit from the pit.
How far can a lot be from the pit?
The furthest service drop run from a pit to the property boundary entry must not exceed 25 m under NBN's pit and conduit standard.
How many lots can share one pit?
NBN's standard allocates typically four lots, and up to eight, to a service drop or boundary pit, subject to the conduit limits for that pit type.
Can a pit go in a driveway?
Pits should be kept clear of driveways and proposed driveways. Where there is no alternative, NBN requires a high strength pit.
Do I need an NBN application before the design?
No. You can get a quote and start design before your application exists. The premises count in the design must match your stage application when it is submitted.