New build plumbing checklist for owner-builders

Most production builders have plumbing scope locked down because they do hundreds of houses. Owner-builders are doing one — easy to miss things. Here's what to think about, in roughly the order it matters during the build.

1. Pre-design — get your plumber involved before the slab is drawn

Most plumbing scope problems start at the design stage. By the time you've got engineered slab drawings and trusses ordered, moving a wet area is expensive. Bring your plumber in when the floor plan is still in flux — we'll flag where drains are going to fight the slab grade, where you'll need an over-floor waste pipe, where a kitchen is too far from existing services.

2. Sewer connection — where and how

Before anything else, confirm:

• Is there a council sewer main at your boundary? If not, you're on septic or on-site treatment, and that changes everything.
• Where does the connection come into the lot, and at what depth? This dictates whether your slab gradient lines up with the connection or not.
• What does the council require for the connection point — riser, inspection chamber, surveyor's certificate?

If your sewer connection is 600mm below natural ground level, you can't have a floor 300mm below natural ground level — the drain can't run uphill. Sounds obvious, gets missed.

3. Stormwater plan

Council will want a stormwater drainage plan as part of your building approval. Roof water, surface water, sub-soil — where does it go? Options are gully connection to street, discharge to legal point, or on-site infiltration. Each has different cost and engineering implications. Sort this with your hydraulic engineer before slab.

4. Pre-slab penetrations and set-outs

This is the most time-pressured part of a new build for the plumber. Once the slab is being prepared for pour, every drain penetration, every sleeve, every waste outlet has to be set out perfectly — because once concrete is around it, it's not moving.

Things we set out at this stage:

• Sewer drainage runs at correct grade
• Stormwater pits, pipes and connections
• Set-out points for toilet, basin, shower, kitchen sink, laundry tub, dishwasher
• Hot water unit drain (if external)
• Gas sleeve for future LPG bottle line or natural gas connection
• Water supply entry sleeve

Mistakes here are the most expensive in the whole build. Don't rush this.

5. Pressure regulator — install one

Mains water pressure on the Gold Coast can spike to 800+ kPa, which is above what household pipework is rated for and will cause taps and fittings to fail early. A pressure-limiting valve (typically set to 500 kPa) installed at the meter is cheap insurance and required by AS3500 for any new install. Don't skip it.

6. Hot water — chose the right system for the slab

This is the moment to plan for solar hot water (panels on the roof) or heat pump (external unit on a slab pad). If you decide later, retrofit is messy. Things to consider:

• Heat pump: needs a small concrete pad outside, ventilation space, electrical supply, drainage for condensate.
• Solar: needs roof structure designed for the tank weight if you're going close-coupled, or roof penetrations for collectors only if you're going split-system.
• Gas continuous-flow: small unit, no tank, but needs gas supply, exhaust clearance and cold/hot/gas connections.

Decide now. Save yourself a $2,000 retrofit fight later.

7. Gas — bottle vs natural, and rough-in for both

Natural gas connection (if available in your street) means a connection from the gas main to your meter, then internal pipework to appliances. LPG means a bottle hardstand outside, regulator and changeover, then internal pipework.

Even if you're not going gas now, run a sleeve from the meter location to the kitchen wall. Adds maybe $200 to the build and means a future gas cooktop install is a one-day job, not a wall-out.

And remember — gas work in QLD is licence-only. Get this done by a licensed gas fitter or it's illegal and your insurance is void.

8. Cold and hot water rough-in

The rough-in is the bit between frame complete and plasterboard going on. We:

• Run cold and hot water lines to every fixture
• Install isolation valves for each fixture (so you can shut off a single tap without killing the whole house)
• Stub out at correct heights, centres and depths for fit-off later
• Pressure-test the system to confirm no leaks
• Coordinate with sparkie for heated towel rail rough-ins

Fixture set-out is critical. A mixer 5mm off centre, a basin spout that doesn't sit over the basin, a shower outlet 30mm too low — these are problems that you find at fit-off when it's too late. Get fixture spec from your design before rough-in starts.

9. Inspections — book ahead, don't get caught

QBCC requires plumbing inspections at specific points: post-rough-in (before walls go up), and post-fit-off (final). Council inspectors and certifiers book out weeks ahead. Get them booked early in the build so you're not waiting on an inspector to be available before the next trade can start.

10. Waterproofing coordination

The plumber finishes rough-in before the waterproofer comes in. The waterproofer seals around every penetration the plumber made. Then the tiler tiles over the waterproofing. Order matters — get any of these out of sequence and you're tearing out finished work.

11. Fit-off — the bit that makes or breaks the look

Fit-off is the visible plumbing work — taps, mixers, showers, basins, toilets, kitchen sink, dishwasher, laundry tub, all installed and connected. Tiny details matter:

• Tapware sits straight (a 1° tilt looks awful when you look down a row of mixers).
• No sealant fingerprints, no scratched chrome.
• Mixer hot/cold sides match standard orientation (hot left, cold right).
• Toilet sits flat to the floor, no wobble.

This is where the difference between a quick install and a careful install really shows. Don't accept "she'll be right" finishes.

12. Final certification and handover

At the end of a new build, your plumber has to certify the plumbing work for QBCC and your private certifier. You should get:

• QBCC Form 4 (plumbing compliance)
• Gas compliance certificate (if gas was installed)
• Backflow prevention test certificate (if a backflow device was installed)
• Pressure test certificates
• Hot water system warranty paperwork registered
• As-built drainage plan

File this paperwork. You'll need it for the certificate of classification, future insurance claims, and the eventual sale of the house.

What good plumbing communication looks like during a build

If your plumber:

• Turns up to site meetings
• Quotes variations in writing before doing them
• Coordinates directly with your other trades
• Books inspections without you having to chase them
• Hands over certifications without you asking twice

…you've got a good one. If any of those are missing, manage the relationship tighter or move on.

We work with owner-builders on the Gold Coast every month. If you're starting a new build and want a plumber that'll slot in cleanly, ring us or send the plans through the contact page. 0472 657 042.