The stages of plumbing a new house on the Gold Coast: rough-in to fit-off

This article goes deep on the four stages of the plumb. If you want the broader picture of a new build first, including who certifies what and the full timeline, read our guide to new build plumbing on the Gold Coast. And if you're an owner-builder wanting the don't-forget list rather than the process, the new build plumbing checklist is the companion to this page. Here we stay on the process: what happens at each stage, who else has to be on site, and what it costs you to get the set-out wrong.

Almost every new home on the Gold Coast is slab-on-ground. That single fact shapes the whole plumb, because the drainage and a fair bit of the water and gas rough-in get buried under concrete that never moves again. That's the thing to keep in your head through all of this: on a slab build, the most important plumbing work happens before you can see a single wall.

Stage 1: Underground / pre-slab rough-in

This is the stage that catches people out, because it happens before the house exists. The block is cleared, the pad is formed up, the formwork and the steel are being set, and somewhere in that window the plumber comes in and lays everything that's going to live under the slab forever.

Sewer and stormwater drainage, set out and laid

The first job is the sewer drainage. Every toilet, basin, shower, bath, kitchen sink, laundry tub and floor waste in the house drains to a network of pipes that has to fall, by gravity, to the council connection point at the boundary. AS3500 sets the minimum grade for that fall, and there's no fudging it: too flat and the pipe blocks and smells, too steep and the water races away and leaves the solids behind. We set out every drain line, dig the trenches, lay the pipe at the right grade on the right bedding, and bring each branch up to the exact spot where a fixture will sit.

Stormwater is the second buried network. Roof water off the gutters and downpipes, plus any surface and sub-soil drainage, all has to get to its legal discharge point, usually a street gully or an inter-allotment drainage easement. On a lot of Gold Coast blocks the land is flat and low, so getting fall on stormwater is genuinely tight, and the pits and pipes have to be planned around the slab levels, not bolted on after.

Under-slab water and gas penetrations

It's not just drainage going in under the slab. We also set the penetrations and sleeves for everything that has to pass through the concrete later:

• The cold water supply entry from the meter into the house
• Sleeves for water lines that pop up inside walls (rather than running through them later)
• A gas sleeve from the meter or bottle location through to the appliance walls, even if gas is a future job
• The set-out points and stub-ups for every wet fixture, positioned to the slab drawings

A sleeve is cheap to put in now and impossible to add later without core-drilling. This is the stage where running one extra conduit for a future outdoor kitchen or a second gas point costs you almost nothing.

The point you cannot un-hear: nothing moves after the pour

Here is the whole reason this stage is so high-stakes. Once the concrete truck arrives and the slab is poured, every drain, every penetration, every set-out point is locked in permanently. If a toilet drain is set out 200mm off, the toilet now sits 200mm off. If a floor waste is in the wrong spot, the shower has to be redesigned around it or the slab has to be cut and the drain relaid, which means jackhammering finished concrete, re-grading the pipe, re-pouring, and waiting for it to cure. That's not a small variation, that's a serious cost and a real delay, and it's why we double-check every set-out against the latest plans before the pour, not the plans from three weeks ago.

Drainage inspection before the pour

Underground drainage has to be inspected and approved before it's covered. In Queensland the buried sanitary drainage is inspected by the relevant inspector while it's still open and visible, often with an air or water test on the drain to prove it holds and there are no leaks in the joints. This is non-negotiable and it's there for a good reason: it's the last chance anyone has to look at the drainage before it disappears under concrete for the life of the house. If the inspection fails, you fix it now while it's easy. You do not pour over un-inspected drainage.

Who else has to be coordinated

This stage lives or dies on coordination with the concreter. The plumber's drainage and penetrations have to be in, inspected and signed off before the concreter can pour, and the concreter is usually working to a tight slot with a booked concrete truck. If the plumber is late, the pour is delayed, and a delayed pour shoves the framer, the roofer and every trade after them back too. The slab levels and the drain grades also have to agree, so the plumber and the concreter (and the engineer's slab drawings) all have to be reading off the same set of levels. This is the one stage where being a day late costs the most, because so much else is queued behind it.

Stage 2: Above-ground / wall rough-in

The slab is poured and cured, the frame is up, the roof is on, and the house is now a skeleton you can walk through. This is when the plumber comes back for the rough-in: all the pipework that runs inside the walls and ceilings, installed before the wall sheeting goes on and hides everything.

Water lines to every fixture

We run hot and cold water lines from the supply through the wall and ceiling cavities to every tap and outlet point in the house. Each fixture gets stubbed out, capped, at the right height, the right centres and the right depth in the wall, ready for the tap or mixer that goes on at fit-off. On the Gold Coast the cold line also has to be planned around the pressure-limiting valve at the meter, because mains pressure here can run high enough to damage fittings over time.

Gas lines in the walls

If the house has gas, the appliance lines get run now too: to the cooktop, the continuous-flow hot water unit, an outdoor BBQ point, whatever's on the plan. Gas pipework in the wall has to be sized for the appliance load and run to the licensed standard. In Queensland gas work is licence-only, so this is done by a licensed gas fitter, full stop. Doing it any other way is illegal and voids your insurance.

Waste and vent pipes

The drainage that started under the slab continues up through the walls as waste and vent pipework. Every fixture needs its waste connected to the drain, and the drainage system needs venting so that water draining out doesn't suck the water out of the traps and let sewer gas back into the house. Those vent pipes run up through the walls and out through the roof, so their position has to be planned around the framing and the roof penetrations.

Setting the points to the tiler and the cabinetmaker

This is the part of rough-in that separates a careful plumber from a careless one. The tap points, outlet points, waste positions and toilet set-out aren't placed to where's convenient in the wall, they're placed to the tiler's finished tile surface and the cabinetmaker's finished joinery. A wall mixer has to land at the right depth so it sits proud of the finished tile by the correct amount, not buried behind it or floating off it. A kitchen sink waste and the tap point have to match the cabinet maker's bench and sink cut-out exactly. A basin spout has to sit centred over where the basin will actually go.

To get this right the plumber needs the final fixtures specified before rough-in starts, and needs to be reading the tiler's tile thickness and the cabinetmaker's joinery drawings. Set a wall mixer out for a 10mm tile when the tiler lays a 20mm stone, and the mixer body ends up the wrong depth in the wall. That's a fit-off-day problem you can't fix without opening the wall back up. Get the fixture spec locked, get it to the plumber, before rough-in.

Pressure test before sheeting

Before a single sheet of plasterboard goes on, the water system is pressure-tested. We charge the pipework up and confirm it holds, which proves there are no leaks in any joint that's about to be sealed inside a wall. Same logic as the drainage inspection: this is the last time anyone can see the pipework, so it gets proven now while a fix is easy. Rough-in is also the stage QBCC inspects before the walls close up.

Who else has to be coordinated

Rough-in is sandwiched between the framer (who has to be finished so the plumber has walls to run pipe in) and the wall sheeting that follows. It also has to dovetail with the electrician, because both trades are fighting for the same wall cavities and ceiling space, and you don't want a water line and a power cable arguing over the same stud bay. And critically, it has to be set out to the tiler and cabinetmaker who come much later, which is why their specs have to exist now. After the plumber, the waterproofer seals around every penetration, then the tiler tiles. Get that sequence out of order and you're tearing out finished work.

Stage 3: Fit-off

The walls are sheeted, the wet areas are waterproofed and tiled, the cabinetry is in, the painting's largely done. Now the house is finished enough that the plumber comes back to install all the visible fixtures onto the points that were roughed in months ago. This is fit-off, and it's the stage that determines how the plumbing actually looks and feels in the finished house.

Installing the fixtures

At fit-off we install and connect the gear:

• Taps, mixers and shower sets onto the roughed-in points
• Toilets, set down and connected to the waste, sitting flat with no rock
• Basins, vanities and the kitchen sink, connected to water and waste
• The bath and any freestanding bath filler
• The laundry tub and the washing machine taps
• The dishwasher connection
• The hot water unit, set on its pad or bracket and connected up

Connecting the gas appliances

The gas cooktop, the continuous-flow hot water unit and any other gas appliance get connected to the lines that were roughed in earlier. This is licensed gas work again, and the appliances aren't just connected, they have to be commissioned properly, which carries into the final stage.

Why fit-off is where the care shows

Everything at this stage is visible and everything is permanent enough to be annoying to redo. Tapware has to sit dead straight, because a mixer tilted a degree off looks awful when you're looking down a row of them. Chrome can't be scratched, sealant can't be smeared, hot has to be on the left and cold on the right. None of this is hard, it's just the difference between a quick install and a careful one. This is also where any rough-in error finally surfaces: a mixer at the wrong depth, a waste in the wrong spot, a spout that doesn't sit over the basin. If the earlier stages were done right, fit-off goes smoothly. If they weren't, this is where it bites.

Who else has to be coordinated

Fit-off can't start until the tiler and the cabinetmaker are done, because the plumber is fixing fixtures onto and into their finished surfaces. It usually overlaps with the painter and the electrician doing their own fit-offs, so the site gets busy. The order matters: tiles and joinery first, then plumbing fit-off, so the fixtures land on finished surfaces rather than the trades clashing.

Stage 4: Final / commissioning and handover

The fixtures are in. The last stage is proving the whole system works, getting the gas commissioned and compliant, and handing over the paperwork that makes the build legal to occupy.

Test everything

We run the lot. Every tap, hot and cold, checked for flow and for the right temperature. Every toilet flushed and refilling cleanly. Every waste and drain checked for flow with no leaks under the basins, the sink, the bath. The hot water system run up to temperature and checked. We're looking for the small stuff that only shows when water actually runs: a weeping connection, a slow-filling cistern, a tap that's cross-threaded hot and cold.

Gas commissioning and compliance

Gas appliances have to be commissioned, not just connected. That means the licensed gas fitter tests the installation for soundness, confirms there are no leaks, checks the appliances are getting the right gas pressure and are burning correctly, and confirms the flues and clearances are right. Done properly, the gas install then gets its compliance certificate. This is the law in Queensland, and it's the part that keeps the house safe.

Certificates and handover

At the end, the plumbing and gas work has to be certified, and you should walk away with the documentation. Depending on what was installed that typically includes the plumbing compliance paperwork, the gas compliance certificate, pressure and drainage test records, the backflow test certificate if a backflow device was fitted, and the hot water system warranty registered. Your certifier needs this compliance paperwork to sign the build off, so it's not optional admin, it's the thing that lets you move in. File it, because you'll want it for insurance and for the eventual sale.

Who else has to be coordinated

The final stage ties back to the private certifier and the QBCC inspection regime. The plumber's certification has to land with the certifier so the certificate of classification can issue. Book the inspections early, because inspectors and certifiers get booked out and a missing slot can hold up the whole handover.

So what does this all cost?

Honestly, it varies, and anyone quoting you a flat number off a blog post is guessing. The plumbing cost on a new home depends on the size of the house, the number of wet areas, the fixtures you choose, whether you're on gas, your hot water system, how hard the drainage and stormwater are on your particular block, and whether you're inland or coastal. The way to get a real number is to send your plans through and get a proper quote against the actual scope. What this article is for is making sure you understand the stages well enough to know nothing important gets skipped or rushed.

The one thing to take away

The order is everything. Underground before the slab, rough-in before the sheeting, fit-off after the tiling and joinery, commissioning at the end. Each stage is locked behind another trade finishing, and the early stages get buried, so the mistakes you make underground or in the wall cost the most to undo. A plumber who knows new builds, who sets out to the final fixtures, and who turns up to the inspections on time saves you far more than they cost.

If you're building on the Gold Coast and want a plumber who'll run these stages cleanly and coordinate with your other trades, send the plans through the contact page or read more about our new build plumbing service. Ring us on 0472 657 042.