On most New Zealand building and renovation projects, drainlayers and plumbers work closely together — but they each hold distinct, legally defined roles. Understanding how these two trades coordinate can save you time, money, and headaches, whether you're building a new home, adding a bathroom, or connecting to the council sewer.
What Each Trade Is Licensed to Do
In New Zealand, both trades are regulated by the Plumbers, Gasfitters and Drainlayers Board (PGDB). The licensing is separate, and the work each trade can legally perform is clearly defined.
- A licensed drainlayer installs, alters, or repairs drains — the underground pipework that carries wastewater and stormwater from your property to the council network or an on-site system (such as a septic tank). This includes everything from the building's external wall outward to the point of connection at the street.
- A licensed plumber handles the pipework inside the building — from fixtures like toilets, sinks, and showers, through the internal waste system, to the point where it exits the building (typically at the external wall or foundation).
Some practitioners hold both licences, which can simplify coordination on smaller jobs. On larger projects, however, you'll often have two separate tradespeople or companies involved.
Where the Two Trades Meet
The critical handover point is usually the drain connection at the building's external wall or floor slab. The plumber's internal waste pipes must align precisely — in both position and fall — with the drainlayer's external drain. If these don't match up, costly rework is required.
This is why communication between the two trades (and with the builder, if there is one) needs to happen early and often. Key coordination points include:
- Pipe invert levels — the height at which the pipe sits inside the trench or slab, which determines the fall (gradient) of the drain
- Pipe locations and penetrations — where pipes pass through the foundation or slab, agreed before concrete is poured
- Inspection openings — placement of access points for future maintenance
- Timing of inspections — both trades may need council or building inspector sign-off at different stages
The Typical Sequence on a New Build
On a new house, the coordination generally follows this order:
| Stage | Who's Involved | Key Task |
|---|---|---|
| Design & consent | Both trades, designer | Agree on drain layout, get building consent |
| Groundworks | Drainlayer | Lay sub-floor drains, set invert levels |
| Slab preparation | Plumber + drainlayer | Confirm pipe penetrations before pour |
| Slab pour | Builder | Concrete locked in — positions are final |
| Framing & fit-out | Plumber | Internal waste and water supply rough-in |
| External connection | Drainlayer | Connect to council sewer or stormwater |
| Inspections | Both trades + council | Sign-off before covering work |
| Completion | Both trades | As-built documentation, producer statements |
Building Consent and Inspections
Most drain and plumbing work on a new build or significant alteration requires a building consent from your local council. The MBIE Building Performance website has guidance on what requires consent and what may be exempt under Schedule 1 of the Building Act — but always confirm with your council before assuming work is exempt.
Both trades are typically required to provide producer statements (PS3 — supervision, PS4 — construction) confirming their work meets the NZ Building Code, particularly clauses G12 (water supplies), G13 (foul water), and E1 (surface water). Inspectors will want to see drains before they are backfilled, so timing is important.
On Renovation and Alteration Projects
On a bathroom renovation or kitchen extension, the coordination is similar but often more compressed. The drainlayer may need to expose or extend existing underground drains to match new fixture positions chosen by the plumber and homeowner. Getting both trades on site at the same time — or at least in close communication — avoids situations where, for example, a new toilet position can't be drained without major excavation.
BRANZ provides technical guidance used by both trades to ensure work meets current standards, including correct pipe falls and materials.
Restricted Work — What Homeowners Cannot Do
Both drainlaying and plumbing are restricted trades in New Zealand. It is illegal for an unlicensed person to carry out, supervise, or certify this work. This applies to homeowners as well. Attempting to do your own drain connections or internal waste plumbing without a licence can:
- Void your home insurance
- Create problems when you sell the property
- Result in fines under the Plumbers, Gasfitters, and Drainlayers Act 2006
Always use a licensed tradesperson and ask to see their current licence. You can verify licences on the PGDB website.
Safety note: Underground drains can involve confined spaces, contact with wastewater, and excavation risks. Leave this work to the professionals.
When to Call a Professional
You should engage both a licensed drainlayer and a licensed plumber (or a dual-licensed tradesperson) whenever you are:
- Building a new home or major addition
- Adding or relocating a bathroom, laundry, or kitchen
- Connecting to a new council sewer or stormwater system
- Installing or upgrading a septic or on-site wastewater system
- Noticing slow drains, gurgling pipes, or wet patches in your yard (possible drain failure)
A good starting point is to find a qualified local drainlayer or plumber through tradedirectory.co.nz, where you can search for licensed professionals in your area.
Certifying Drainlayer
