How to Quote a Plumbing or Drainage Job in NZ — Fixtures, Runs, the Gravity/Pumped Split, and AS/NZS 3500
Updated: Jul 9
Plumbing and drainage quotes in NZ fail on the things the site plan does not show: the fall that will not reach the connection, the inspection points the engineer's notes require, and the fixture schedule that grew between revisions. Here is the quoting sequence that prices what will actually be installed.
By Steve Parker · Trueworks · NZ construction estimation · 5 min
What you'll learn in this post
The takeoff structure: fixtures, runs by diameter, and the drainage design — separately
The gravity-vs-pumped question that moves quotes by five figures
The exclusions and consent interfaces a defensible quote carries
Quick answer: A defensible NZ plumbing/drainage quote prices three layers separately: fixtures (counted per room off the named revision, with rough-in and fit-off as distinct labour), pipe runs (by diameter, material, and actual route under AS/NZS 3500.1/.2 for water and sanitary), and drainage (by the engineer's design, not the site plan — falls, inspection points, and the gravity/pumped decision under AS/NZS 3500.3). The gravity-vs-pumped split is the five-figure question: a pump station, rising main, and electrical supply turn a $8k drainage scope into $25k+. On TC2/TC3 land (Canterbury and mapped liquefaction zones), flexible joints and added inspection points are engineer-specified costs the standard quote misses. Wastage on pipe: ~5-8% on cut runs.
Step 1 — fixtures, with rough-in and fit-off split
Count fixtures per room against the named drawing revision: WCs, basins, showers (heads and outlets separately where specified), baths, sinks, laundry tubs, HWC or continuous-flow units, external taps, washing machine and dishwasher points.
Price rough-in and fit-off as separate labour stages — they happen months apart, between other trades, and a fit-off return visit priced at zero is margin gone. On renovations, add the strip-out and cap-off stage.
The fixture schedule is also the revision trap: bathroom counts change between concept and consent more than almost any other scope. The quote line "fixtures as scheduled on revision X" makes growth a variation.
Step 2 — runs by diameter and route
Water supply (AS/NZS 3500.1) and sanitary plumbing (AS/NZS 3500.2) price by measured route: pipe by diameter and material (PEX, copper, PVC waste), valves, and the vertical drops and subfloor or ceiling routes the plan view flattens. Add 5-8% wastage on cut runs.
Hot-water delivery dead-legs, tempering valves, and any specified recirculation loop are their own lines. A continuous-flow conversion includes the gas line or the electrical-supply interface — name whose scope that interface is.
Step 3 — drainage off the engineer's design, never the site plan
The site plan shows a line to the boundary. The engineer's drainage design shows what you actually price under AS/NZS 3500.3:
Falls and invert levels — whether gravity reaches the connection at compliant grade
The gravity/pumped decision — if the levels do not work, a pump station, rising main, non-return valves, and an electrical supply enter the scope. This is the five-figure swing; price it only off the engineer's design, and if that design is not issued yet, exclude pumped drainage by name
Inspection points and access chambers — count them; on TC2/TC3 land the engineer's notes typically increase the density and specify flexible joints for differential settlement, both above standard allowances
Stormwater attenuation — detention tanks and flow-control devices on infill sites are engineer-designed items with their own PS chain; in or out, by name
The connection itself — council connection fees, road-opening consents, and traffic management at the boundary are real costs; name whose they are
Step 4 — exclusions, certification, validity
The defensible plumbing/drainage quote carries:
The drawing and drainage-design revisions priced, by name
Gravity drainage assumed; pumped systems excluded unless engineer-designed and priced
Ground conditions assumed (rock excavation, dewatering, and contaminated spoil excluded)
Council fees, connection charges, and traffic management allocated by name
As-laid plans, CCTV if required, and inspection attendance stated (what is included, what re-attendance costs)
30-60 day validity — pipe and fitting pricing moves with resin and metals
Certification: the craftsperson certification and council inspections are yours to schedule; producer-statement support on engineer-designed elements (pump stations, attenuation) belongs to whoever the quote names.
FAQ — quoting plumbing and drainage in NZ
Q1: Can I price drainage off the architect's site plan? No. The site plan shows intent; AS/NZS 3500.3 compliance lives in falls, invert levels, and inspection-point density, which come from the engineer's design. Quotes priced off the site plan own the gap when the design lands.
Q2: Who pays when gravity will not reach the connection? Whoever the quote says. A pump station is $15-25k+ of scope swing. "Gravity drainage assumed; pumped system if required priced as variation off the engineer's design" is the line that keeps it a variation.
Q3: What changes on TC2/TC3 land? Engineer-specified flexible joints, tighter inspection-point spacing, and settlement allowances under the MBIE guidance — all above standard residential allowances. Price off the geotech-informed design, and name its revision.
Q4: How should rough-in and fit-off be priced? As separate stages with separate site visits. The months between them belong to other trades; a quote that prices one continuous visit funds the return trip itself.
Q5: What wastage factor for pipework? 5-8% on cut runs, higher on complex subfloor routes. Fittings price by count, not factor.
Get your next plumbing tender measured properly
Drawings + the drainage design + 5 business days = a fixture schedule, run takeoff, and drainage pricing with the gravity/pumped risk named and your exclusions drafted.
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About Trueworks
Trueworks is built by Steve Parker — 20 years on the analytical side of NZ construction. Variation reviews, contract advisory, programme review, and AI-augmented document workflows. Trueworks is the productisation of that practice for builders: same defensible analysis, at a price and pace a NZ builder can actually use.
Every report is checked and signed off by me personally before it goes out. If you have a plumbing or drainage tender closing, the easiest way to find out if Trueworks is useful is to send the drawings.
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