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Exam Review

Key Facts: NZ Certifying Drainlayer Exam

100

Practice Questions

OpenExamPrep

65-70

Exam Questions

PGDB

2.5 hours

Time Limit

PGDB

NZ$410

Exam Fee (GST incl.)

PGDB

~25%

Paper Design Component

PGDB

AS/NZS 3500

Key Standard

AS/NZS 3500.2 & .3

The NZ PGDB Certifying Drainlayer Examination is the Plumbers, Gasfitters and Drainlayers Board's registration exam for certifying drainlayers, the highest drainlaying class. It runs 2.5 hours with about 65-70 questions: roughly 75% answered electronically (multiple choice, numerical, inline and multi-select) and about 25% as design work on paper, and it costs NZ$410 (GST inclusive). Relevant codes and standards (AS/NZS 3500 and Building Code clauses) are supplied as reference PDFs during the exam. Content spans foul-water and stormwater drainage to AS/NZS 3500.2 and 3500.3, gradients, falls and invert levels, pipe materials and jointing, inspection and testing, on-site wastewater systems to AS/NZS 1547, the NZ Building Code (G13 and E1), and the PGD Act 2006 and regulations. Passing lets a registered drainlayer certify their own work and supervise others' restricted drainlaying. This free prep includes 100 research-based practice questions with explanations and an AI tutor.

Sample NZ Certifying Drainlayer Practice Questions

Try these sample questions to review concepts for the NZ Certifying Drainlayer exam. Each question includes a detailed explanation. Start the interactive quiz above for the full 162+ question experience with AI tutoring.

1Under G13/AS2 Table 2, what is the maximum discharge-unit loading for a DN100 drain laid at a gradient of 1:80?
A.122 discharge units
B.149 discharge units
C.205 discharge units
D.255 discharge units
Explanation: G13/AS2 Table 2 gives a maximum loading of 149 discharge units for a DN100 drain at 1:80. The permitted gradient is selected from both pipe diameter and calculated discharge-unit loading; there is no single size-only minimum grade.
2A DN150 foul-water drain has a calculated load of 600 discharge units. Under G13/AS2 Table 2, what is the flattest listed gradient that can carry that load?
A.1 in 120
B.1 in 140
C.1 in 160
D.1 in 180
Explanation: At 1:160 a DN150 drain is rated for 611 discharge units, so it can carry 600. The next flatter entry, 1:180, is rated for only 558 discharge units. Therefore 1:160 is the flattest listed compliant choice.
3A DN100 drain is laid at 1 in 60 over a horizontal run of 30 m. What is the total fall?
A.300 mm
B.500 mm
C.600 mm
D.1800 mm
Explanation: Fall equals length divided by the grade ratio: 30 m / 60 = 0.5 m = 500 mm. This calculation sets the difference in invert level between the upstream and downstream ends of the run.
4The invert of a drain is best described as which part of the pipe?
A.The crown or top of the internal bore
B.The lowest point of the internal bore
C.The external soffit of the pipe
D.The centre line of the pipe
Explanation: The invert is the lowest point of the internal bore of a pipe or channel. Invert levels are used to set grades, calculate falls, and ensure correct connection heights between pipes and at junctions.
5Under G13/AS2, how must a non-vent connection enter a foul-water drain?
A.Follow any angle when both pipe diameters match
B.Use ≤45° upstream and point the junction with flow
C.Enter square at 90° to shorten the branch route
D.Point upstream so the receiving flow washes into the branch
Explanation: G13/AS2 requires a non-vent connection to use a junction with an upstream angle no greater than 45° and to be installed in the direction of flow. This arrangement reduces obstruction and blockage risk.
6For a new DN100 equal-junction installation in a graded drain, what minimum incline applies to the branch entry under G13/AS2?
A.At least 5° above horizontal
B.At least 15° above horizontal
C.At least 45° above horizontal
D.Exactly 90° above horizontal
Explanation: For a new DN100 equal-junction connection in a graded drain, G13/AS2 requires the branch entry to be inclined at least 15° above horizontal. The document separately provides stated on-grade exceptions for repair, maintenance or extension work and where no WC pan is connected upstream.
7When an unequal junction connects a smaller branch to a graded drain under the AS/NZS 3500.2 rules cited by G13/AS3, where must the smaller branch invert be?
A.At least 10 mm below the receiving-drain invert
B.Level with the receiving-drain soffit
C.At least 10 mm above the receiving-drain soffit
D.Exactly 15 mm below the receiving-drain crown
Explanation: For an unequal junction, the smaller branch invert must enter at least 10 mm above the soffit of the receiving drain. This is a separate requirement from the inclination and direction rules that apply to junction fittings.
8Which NZ Building Code clause covers foul water (sanitary drainage)?
A.E1 Surface Water
B.G12 Water Supplies
C.G13 Foul Water
D.E2 External Moisture
Explanation: NZ Building Code Clause G13 covers foul water. G13/AS3 cites AS/NZS 3500.2:2021, with New Zealand modifications, as one Acceptable Solution for sanitary plumbing and drainage.
9Which NZ Building Code clause governs the disposal of stormwater and surface water?
A.G13 Foul Water
B.E1 Surface Water
C.G12 Water Supplies
D.G14 Industrial Liquid Waste
Explanation: Clause E1 Surface Water of the NZ Building Code covers the collection and disposal of stormwater and surface water so that it does not damage other property or endanger people. Drainlayers must distinguish E1 (stormwater) from G13 (foul water) systems, which must remain separate.
10Which standard is cited by E1/AS2 as an Acceptable Solution for stormwater drainage?
A.AS/NZS 3500.1:2021
B.AS/NZS 3500.3:2021
C.AS/NZS 3500.2:2021
D.AS/NZS 1547:2012
Explanation: E1/AS2 cites AS/NZS 3500.3:2021 Stormwater drainage, subject to the modifications stated in E1/AS2. E1/VM1 and E1/AS1 provide other compliance pathways for surface-water work.

About the NZ Certifying Drainlayer Exam

The Certifying Drainlayer Examination is the PGDB's registration exam for the highest class of drainlayer in New Zealand. It is a 2.5-hour, computer-based exam of about 65-70 questions (roughly 75% electronic multiple-choice and numerical items plus a 25% paper design component) costing NZ$410. Passing it lets a registered drainlayer apply to certify their own work and supervise the restricted drainlaying of others.

Exam sponsor: Plumbers, Gasfitters and Drainlayers Board (PGDB). The requirements and fees below concern the certification or admission exam, separate from our free practice resources.

Assessment

65-70 questions over 2.5 hours; about 75% answered electronically (multiple choice, numerical, inline and multi-select) and about 25% design work answered on paper. The paper design questions are marked separately within 10 working days. Codes and standards are supplied as reference PDFs in the exam. This practice bank is 100 selected-response items.

Time Limit

2.5 hours

Passing Score

Competency-based standard set by the PGDB

Exam / Certification Fees

NZ$410.00 (GST inclusive)

Exam sponsor website

Fees, eligibility, and exam policies can change. Confirm them with the exam sponsor before applying or paying.

Our practice resources: topics covered

We aim to reflect publicly available exam outlines and topic information in our study resources. Coverage, format, and difficulty may differ from the actual exam, and we cannot guarantee that every detail is accurate or current. Confirm exam requirements, fees, and policies with the official exam sponsor.

30%

Foul-Water & Stormwater Drainage

Separated systems, junctions and bends, gully traps and water seals, ventilation, discharge pipes, fixture-unit sizing, sewer connection, rising mains, and overflow relief under AS/NZS 3500.2 and 3500.3

16%

Inspection & Testing

Water and air testing, CCTV condition assessment, pre-backfill inspection, leak detection, confined-space and gas hazards, trench safety, and service location

14%

PGDB Act & Regulations

PGD Act 2006, registration and practising licences, certifying authority, supervision of restricted work, records of work, CPD, trade waste, and exam format

12%

On-Site Wastewater Systems

AS/NZS 1547 septic tanks and AWTS, primary and secondary treatment, soakage trenches and irrigation, percolation testing, design loading rates, setbacks, and resource consents

12%

Pipe Materials & Jointing

uPVC, vitrified clay and other DWV materials, solvent-cement and rubber-ring joints, joint preparation, dissimilar-material adaptors, bedding, cover, and backfill

10%

Gradients, Falls & Invert Levels

Minimum grades for DN100 and DN150, fall and grade calculations, invert levels, setting out with laser levels and boning rods, and avoiding over-steep grades and backfall

6%

NZ Building Code

Clause G13 Foul Water and E1 Surface Water, AS/NZS 3500.2 and 3500.3 as Acceptable Solutions, compliance pathways, and service separation

Preparing for the NZ Certifying Drainlayer Exam

What You Need to Know

  • Passing score: Competency-based standard set by the PGDB
  • Assessment: 65-70 questions over 2.5 hours; about 75% answered electronically (multiple choice, numerical, inline and multi-select) and about 25% design work answered on paper. The paper design questions are marked separately within 10 working days. Codes and standards are supplied as reference PDFs in the exam. This practice bank is 100 selected-response items.
  • Time limit: 2.5 hours
  • Exam / certification fees: NZ$410.00 (GST inclusive) Official sources

Using Our Practice Resources

  • Work through all 162 available questions
  • Review every answer and explanation
  • Track weak areas and revisit them
  • Use our AI tutor for tough concepts

NZ Certifying Drainlayer: Suggested Study Strategy

1Weight your study toward foul-water and stormwater drainage, inspection and testing, and the PGD Act - together they are the bulk of the exam
2Memorise the core grades: DN100 minimum 1 in 60 and DN150 minimum 1 in 100, and practise fall = length / grade ratio until it is automatic
3Know AS/NZS 3500.2 (foul water, G13) versus AS/NZS 3500.3 (stormwater, E1) and never cross-connect the two systems
4Practise the design/paper questions - sketching drain layouts, junctions, gradients and invert levels - because about 25% of marks are paper-based
5Be confident on testing methods (water vs air test, rising-main pressure test) and confined-space and trench safety
6Complete all 100 practice questions and review every miss with the AI tutor before sitting the exam

Frequently Asked Questions

How many questions are on the PGDB Certifying Drainlayer exam and how long is it?

The Certifying Drainlayer examination has about 65-70 questions and runs for 2.5 hours. Roughly 75% are answered electronically (multiple choice, numerical, inline and multi-select) and about 25% are design questions answered on paper, which are marked separately.

How much does the Certifying Drainlayer exam cost?

The PGDB Certifying Drainlayer examination fee is NZ$410.00 (GST inclusive) per sitting. Registration and your annual practising licence are charged separately once you pass.

What is the difference between a registered drainlayer and a certifying drainlayer?

A Certifying Drainlayer holds the highest drainlaying class. They can carry out and certify their own restricted drainlaying work without supervision and may supervise the restricted work of others, remaining accountable for its compliance.

What topics does the Certifying Drainlayer exam cover?

It covers foul-water and stormwater drainage to AS/NZS 3500.2 and 3500.3, gradients, falls and invert levels, pipe materials and jointing, inspection and testing, on-site wastewater systems to AS/NZS 1547, the NZ Building Code (G13 and E1), and the PGD Act 2006 and regulations.

Are codes and standards provided during the exam?

Yes. The relevant codes and standards, such as AS/NZS 3500 and Building Code clauses, are supplied as reference PDFs within the exam, so it tests your ability to find and apply requirements rather than memorise them. Hardcopy references can be arranged through special assessment conditions.

Is this free Certifying Drainlayer practice as good as paid prep?

Our 100 practice questions cover the same content areas as the certifying exam, with a teaching explanation for every answer plus free daily AI tutor interactions. All content is free forever and updated for 2026.