Plumbing Rough-In Inspection Requirements for Residential Builds (AU)

What it is

A plumbing rough-in inspection is the stage where pipework is checked after installation but before it is covered by slab concrete, wall linings or ceiling sheets. In Australia the work must be done by a licensed plumber and the rough-in is the last realistic chance to find faults without breaking finished surfaces.

The inspection sits inside the plumbing approval pathway run by the state regulator. AS/NZS 3500 sets the technical rules. The National Construction Code Volume Three (the Plumbing Code of Australia) calls up that standard, and each state plumbing Act gives it legal force.

Two main types of rough-in get inspected on a typical residential build. The first is the in-slab or below-ground rough-in for sanitary drainage and cold water mains. The second is the in-wall rough-in for hot and cold supply, waste branches and gas where present. Both have to be tested and signed off before the next trade closes them in.

What the inspector actually checks

Pipe layout and routing

The inspector confirms pipework matches the approved hydraulic plans. Drainage runs are checked for correct diameter, branch locations and venting. Cold and hot water lines are checked for material type, jointing method and protection where they pass through concrete, brickwork or framing. Penetrations through fire-rated walls need fire collars or approved sealants.

Grades and falls

Sanitary drainage falls are the single most checked item. AS/NZS 3500.2 sets minimum grades of 1 in 60 for DN 100 and 1 in 40 for DN 80 and below, with maximum grades to stop solids stranding. The inspector uses a level or laser to confirm fall along each run and through every junction. Reverse grades or flat runs at junctions get marked for rework before the slab is poured.

Pipe supports and protection

Supports are checked for spacing and type. Copper, PEX and HDPE all have different maximum bracket spacings. Pipes in slab need approved sleeving so concrete cure does not bond to the pipe and crack joints during ground movement. Pipes through bottom plates need nail plates if the cover is less than 50 mm.

Flushing of supply lines

Before pressure test, supply lines must be flushed to clear swarf, sealant tape and debris. The inspector may ask to see flushing residue or a flushing certificate from the plumber. Skipping flushing is a common cause of tap cartridge failure in the first year.

Pressure and hydraulic tests

The hydraulic test is the headline event of the rough-in. AS/NZS 3500.1 sets the pressure for cold and hot water at 1500 kPa held for a minimum of 30 minutes with no measurable pressure drop. Sanitary drainage gets a hydrostatic head test (water filled to the highest fitting) or an air test at 30 kPa held for at least 3 minutes per AS/NZS 3500.2. Stormwater is tested at the same standard. The inspector watches gauges, checks for visible leaks and signs the result in the inspection record.

Clearances and access

Penetrations through bearers, joists and studs must keep within the structural drill-and-notch rules in the timber framing code. Hot water heater rough-ins need correct clearances for relief drain, tempering valve location and gas line approach where relevant.

Tundish, vent and trap arrangement

Inspectors confirm trap depths (60 to 75 mm water seal for most fixtures), vent positions, and tundish details for hot water expansion and tempering valve drain lines. Missing or undersized vents cause trap siphoning and back-pressure later.

When the inspection happens

In a slab build the underground drainage and any in-slab water lines must be tested and inspected before the pour. In a suspended floor build the bottom-plate penetrations and supply manifolds are checked before bottom-plate fix. Wall rough-in happens after framing and before plasterboard. Some states require a separate notification for each.

Council or private hydraulic surveyors carry out the inspection in NSW, Victoria, WA, SA, Tasmania, ACT and NT. Queensland uses the Plumbing Inspector role under the QBCC. Booking lead times of 24 to 72 hours are normal.

Common reasons rough-in fails

• Reverse fall or flat sections in drainage
• Missing or undersized stack vent
• Slab penetrations without sleeving
• Hot and cold lines crossed at the tempering valve manifold
• Pressure test gauge drops below the threshold inside the 30-minute hold
• No tundish or visible drain on the relief valve
• Gas line tee in wrong location for the heater set-out

What to give the inspector

The plumber should have the hydraulic plans on site, the approved set-out drawings, the gauge for the pressure test, and any product certification for backflow devices and tempering valves. Photographs of in-slab work taken before the pour help if a defect is found later.

Related rules

AS/NZS 3500.1 covers water services. AS/NZS 3500.2 covers sanitary plumbing and drainage. AS/NZS 3500.3 covers stormwater. AS/NZS 3500.4 covers heated water services. NCC Volume Three (Plumbing Code of Australia) calls up all four parts as primary referenced documents.