In Part 1 of our plumbing series, we covered the key design and planning decisions every owner builder should make before construction starts.
In this second blog, we dive into what can go wrong once plumbing work begins.
From rough-in blunders to last-minute fixture swaps, Nathan Rich from KNR Plumbing (yep, a real licensed plumber) shares the most common mistakes he sees and how you can avoid them.
Plumbing slip-ups don’t just cost money, they can delay your build and cause long-term headaches.
Here’s what to watch out for.
Plumbing Mistake #1: Not Understanding the Difference Between Rough-In and Fit-Off
One of the first plumbing stages is the rough-in, where pipes are laid through walls and floors before plaster goes up. The fit-off happens much later, once tiling, waterproofing, and cabinetry are complete, and fixtures like taps and sinks are installed.
“Your rough-in happens before the walls are sheeted. If anything's wrong and the walls go on, it's a big deal to fix,” says Nathan.
Get this wrong, and you may be pulling off tiles or cutting into brand-new walls.
✅ Pro tip: Confirm the rough-in is complete and correct before walls are closed.
Plumbing Mistake #2: Forgetting to Order Your Tapware and Fixtures
Nathan's #1 piece of advice? Have all your tapware and fixtures ready before rough-in.
“Too many times I turn up to rough-in and the owner builder hasn’t bought their mixer taps yet. I can’t install what I don’t have.”
Every fixture, like your vanity, toilet, bath, and especially mixer taps, needs to be physically available at rough-in to get accurate placement.
✅ Pro tip: Don’t book your plumber until your fixtures are selected and delivered.
Plumbing Mistake #3: Changing Fixtures Mid-Build
You might find a new toilet you like halfway through the build but if your plumbing has already been set for something else, changing your mind can get expensive.
“I’ve had owners change their toilet choice, and the new one didn’t match the original plumbing. We had to move water points and rework everything.”
✅ Pro tip: Lock in your choices before rough-in and stick to them.
Plumbing Mistake #4: Hiring the Cheapest Trade
Budget is important but cheap trades can lead to shortcuts, missed steps, or even non-compliant work.
“Some builders use cheaper trades or unsupervised apprentices to cut costs. I’ve seen pipes laid incorrectly or not clipped properly. That leads to water hammer or drainage problems.”
✅ Pro tip: Always hire a licensed plumber and check their reviews and insurance.
Plumbing Mistake #5: Rushing the Job
In a rush to meet deadlines, some builders or owner builders skip critical checks.
“New builds are often rushed. Inspectors can miss things. It’s better to allow time to do it right than deal with plumbing issues later.”
✅ Pro tip: Build in time for inspections and don’t rush your trades.
What's next in the Plumbing Series?
Plumbing mistakes can sneak up on even the most organised owner builder but they’re often easy to avoid with the right knowledge and timing. From rough-in readiness to locking in your fixtures, Nathan’s advice helps you stay one step ahead.
In Part 3 of our series, we’ll dive into the plumbing regulations you must follow, including inspections, permits, and those unexpected requirements. Like bum gun compliance and yes, you read that correctly 😅.
Stay tuned Owner Builders 🏡
About Nathan Rich – KNR Mechanical Plumbing
Nathan runs KNR Mechanical Plumbing on the Sunshine Coast and has built a solid reputation for being friendly, down-to-earth, and great at what he does.
With loads of experience in residential builds and renos, Nathan takes pride in doing the job right. No shortcuts, just honest advice and quality work.
If you’re after a plumber who actually cares about your build and has experience working with owner builders, Nathan’s your guy!
Have questions or a rough-in horror story? Join our free Private Facebook group with over 12,000 other owner builders sharing tips and support – click to join!
