I85PREP
⌘ K
NZ Certifying Drainlayer study materials
NZ Certifying Drainlayer study resources

NZ Certifying Drainlayer practice questions

One question at a time. Build your NZ Certifying Drainlayer understanding.

First 50 of 200 questions. Each one lists the choices, the correct answer, and an explanation. The checker at the top of this page saves progress in this browser when it is available.

Continue in the practice tool above to load more questions, 50 at a time.

Question 1Legislation, regulations and standards for drainlaying

Which Act is the principal statute that establishes the registration and licensing regime for drainlayers in New Zealand?

  1. The Health and Safety at Work Act 2015
  2. The Building Act 2004
  3. The Resource Management Act 1991
  4. The Plumbers, Gasfitters and Drainlayers Act 2006 Correct answer.

Explanation

The Plumbers, Gasfitters and Drainlayers Act 2006 establishes the Board and the registration and licensing system for drainlayers. It also defines restricted work and disciplinary powers.

Question 2Legislation, regulations and standards for drainlaying

To carry out drainlaying for payment in New Zealand, a person must:

  1. be registered and licensed Correct answer.
  2. hold a licence alone
  3. work under a builder
  4. hold a building consent

Explanation

Registration confirms the person is qualified and fit to be registered, while a current practising licence is required before carrying out licensed drainlaying work. Both are needed.

Question 3Legislation, regulations and standards for drainlaying

Which New Zealand Building Code clause sets performance requirements for foul water drainage?

  1. G13 Foul Water Correct answer.
  2. G14 Industrial Liquid Waste
  3. E1 Surface Water
  4. G12 Water Supplies

Explanation

Clause G13 Foul Water sets performance requirements for the collection, storage and disposal of foul water from buildings. G12 covers water supplies and G14 covers industrial liquid waste.

Question 4Legislation, regulations and standards for drainlaying

A drainlayer needs to check the Acceptable Solution requirements for installing sanitary plumbing and drainage. Which standard is the main reference?

  1. AS/NZS 3500.2 Correct answer.
  2. AS/NZS 3500.4
  3. AS/NZS 3500.3
  4. AS/NZS 3500.1

Explanation

AS/NZS 3500.2 is the plumbing and drainage standard dealing with sanitary plumbing and drainage. AS/NZS 3500.1 covers water supply, AS/NZS 3500.3 covers stormwater and AS/NZS 3500.4 covers heated water.

Question 5Legislation, regulations and standards for drainlaying

Which standard is the primary reference for stormwater drainage design and installation?

  1. AS/NZS 3500.2
  2. AS/NZS 3500.1
  3. AS/NZS 3500.3 Correct answer.
  4. AS/NZS 3500.4

Explanation

AS/NZS 3500.3 is the stormwater drainage standard. It covers design, installation and products for surface water drainage.

Question 6Legislation, regulations and standards for drainlaying

Which organisation is responsible for granting building consents for drainage work?

  1. The territorial authority Correct answer.
  2. WorkSafe New Zealand
  3. The Plumbers, Gasfitters and Drainlayers Board
  4. Taumata Arowai

Explanation

Territorial authorities are building consent authorities and grant building consents for drainage work. The Plumbers, Gasfitters and Drainlayers Board licenses tradespeople but does not issue building consents.

Question 7Legislation, regulations and standards for drainlaying

Before a newly laid private drain is backfilled, the usual quality check is to:

  1. flush it with stormwater
  2. paint the joints with solvent cement
  3. fit the inspection opening cover
  4. test it for watertightness Correct answer.

Explanation

Drains are normally tested for watertightness before backfilling so defects can be found and repaired while accessible. The building consent will also usually require an inspection before the work is covered.

Question 8Legislation, regulations and standards for drainlaying

Stormwater from a new dwelling must be discharged to:

  1. the trade waste system
  2. the foul sewer
  3. a septic tank
  4. the stormwater system Correct answer.

Explanation

Stormwater must be kept separate from foul water and discharged to the stormwater system, not the foul sewer. Cross-connections can overload the sewer and are prohibited.

Question 9Legislation, regulations and standards for drainlaying

The New Zealand Building Code is set out in which instrument?

  1. The Building Regulations 1992 Correct answer.
  2. The Plumbers, Gasfitters and Drainlayers Act 2006
  3. NZS 3604
  4. The Building Act 2004

Explanation

The New Zealand Building Code is Schedule 1 of the Building Regulations 1992. The Building Act 2004 requires compliance with the code but does not itself contain the code clauses.

Question 10Legislation, regulations and standards for drainlaying

Which New Zealand Building Code clause applies to industrial liquid waste discharged to drainage systems?

  1. G13 Foul Water
  2. G14 Industrial Liquid Waste Correct answer.
  3. G15 Solid Waste
  4. E1 Surface Water

Explanation

Clause G14 Industrial Liquid Waste covers the discharge of industrial liquid waste to drainage systems. G13 deals with ordinary foul water from sanitary fixtures and appliances.

Question 11Legislation, regulations and standards for drainlaying

A food business proposes to discharge trade waste to the council sewer. What approval is normally required?

  1. A trade waste permit Correct answer.
  2. A resource consent from the Board
  3. A water supply permit
  4. A building consent only

Explanation

Discharging trade waste to a council sewer normally requires a trade waste permit from the territorial authority. The permit sets pretreatment and discharge conditions.

Question 12Legislation, regulations and standards for drainlaying

After completed building work is found to comply with the building consent and Building Code, the territorial authority issues a:

  1. certificate of work
  2. practising licence
  3. producer statement
  4. code compliance certificate Correct answer.

Explanation

A code compliance certificate is issued by the territorial authority once it is satisfied that completed building work complies with the building consent and the Building Code.

Question 13Legislation, regulations and standards for drainlaying

A certifying drainlayer's main statutory role in relation to building work is to:

  1. issue code compliance certificates for buildings
  2. approve connections to public stormwater mains
  3. certify specified drainage work as compliant Correct answer.
  4. grant building consents for drainage

Explanation

A certifying drainlayer is registered and licensed to certify specified drainage building work for the territorial authority. This certification supports the building control process but does not replace building consents or code compliance certificates.

Question 14Legislation, regulations and standards for drainlaying

A practising licence issued by the Plumbers, Gasfitters and Drainlayers Board must normally be renewed:

  1. only when changing employer
  2. every five years
  3. every year Correct answer.
  4. every three years

Explanation

Practising licences are issued for a limited period and are normally renewed annually. Working without a current practising licence is an offence.

Question 15Legislation, regulations and standards for drainlaying

A complaint about the competence or conduct of a registered drainlayer is made to:

  1. the local district court
  2. WorkSafe New Zealand
  3. the Plumbers, Gasfitters and Drainlayers Board Correct answer.
  4. the building consent authority

Explanation

The Plumbers, Gasfitters and Drainlayers Board handles complaints and disciplinary matters about registered practitioners. Courts deal with prosecutions, not routine competence complaints.

Question 16Legislation, regulations and standards for drainlaying

What record is normally required when a certifying drainlayer completes drainage work that is exempt from building consent?

  1. A code compliance certificate
  2. An inspection notice from WorkSafe
  3. A certificate of work Correct answer.
  4. A building consent amendment

Explanation

A certifying drainlayer can issue a certificate of work for certain drainage work that does not require a building consent. The certificate records that the work complies with the relevant requirements.

Question 17Legislation, regulations and standards for drainlaying

A drainlayer discovers that a new drain crosses a public sewer main. Before altering the public main, the drainlayer should:

  1. ask for a code compliance certificate
  2. obtain approval from the network operator Correct answer.
  3. complete the work and notify the Board
  4. backfill and record it on the as-built plan

Explanation

Public sewer mains are assets controlled by the territorial authority or network operator. Approval is needed before altering or connecting to them, and damage must be reported.

Question 18Legislation, regulations and standards for drainlaying

A building consent is required for a new drainage connection unless the work is:

  1. inspected by the territorial authority
  2. carried out by a registered drainlayer
  3. covered by a producer statement
  4. exempt building work under Schedule 1 Correct answer.

Explanation

Building consent is required unless the work falls within the exempt building work in Schedule 1 of the Building Act 2004. Being registered or using a producer statement does not remove the consent requirement.

Question 19Legislation, regulations and standards for drainlaying

Before covering drainage work that requires a building consent inspection, the drainlayer must:

  1. have the work certified by WorkSafe
  2. notify the authority and obtain clearance Correct answer.
  3. lodge an as-built plan with the Board
  4. apply for a code compliance certificate

Explanation

Consent conditions usually require notice and inspection before drainage is covered. Covering work before inspection can require it to be exposed again.

Question 20Legislation, regulations and standards for drainlaying

The primary responsibility for ensuring drainage work complies with the Building Code rests with:

  1. the person carrying out the work Correct answer.
  2. the pipe manufacturer
  3. the territorial authority
  4. the homeowner

Explanation

The person carrying out building work, including the drainlayer, must ensure it complies with the Building Code and the building consent. Others may have oversight roles, but the primary duty sits with the installer.

Question 21Legislation, regulations and standards for drainlaying

Which legislation requires a resource consent for discharging treated wastewater to a river?

  1. Resource Management Act 1991 Correct answer.
  2. Health and Safety at Work Act 2015
  3. Building Act 2004
  4. Plumbers, Gasfitters and Drainlayers Act 2006

Explanation

The Resource Management Act 1991 controls discharges to water, land and air through resource consents. Building and trade licensing legislation does not authorise environmental discharges.

Question 22Legislation, regulations and standards for drainlaying

Which agency is the water services regulator established under the Water Services Act 2021?

  1. The territorial authority
  2. Taumata Arowai Correct answer.
  3. WorkSafe New Zealand
  4. The Plumbers, Gasfitters and Drainlayers Board

Explanation

Taumata Arowai is the water services regulator under the Water Services Act 2021. It oversees drinking-water supply and regulation of wastewater and stormwater networks.

Question 23Legislation, regulations and standards for drainlaying

NZS 4404 is primarily used for:

  1. subdivision infrastructure Correct answer.
  2. gas installation work
  3. drinking-water treatment
  4. sanitary plumbing inside buildings

Explanation

NZS 4404 provides standards for land development and subdivision infrastructure, including stormwater and wastewater reticulation. It is not the internal sanitary plumbing standard.

Question 24Legislation, regulations and standards for drainlaying

A drainlayer is excavating a deep trench in a public road. Which legislation imposes the primary duty to manage excavation hazards?

  1. Building Act 2004
  2. Health and Safety at Work Act 2015 Correct answer.
  3. Resource Management Act 1991
  4. Plumbers, Gasfitters and Drainlayers Act 2006

Explanation

The Health and Safety at Work Act 2015 imposes duties on PCBUs to manage risks, including excavation and trenching hazards. Building and resource legislation may also apply, but the primary worker-safety duties are under the health and safety legislation.

Question 25Legislation, regulations and standards for drainlaying

What is the legal effect of complying with an Acceptable Solution under the Building Act 2004?

  1. It must be accepted as complying with the Building Code for the matters it covers. Correct answer.
  2. It is a mandatory method for all drainage work.
  3. It overrides the Building Code where local conditions differ.
  4. It is a manufacturer's guide with no legal status.

Explanation

An Acceptable Solution is a means of compliance issued under the Building Act 2004. If building work complies with a relevant Acceptable Solution, it must be accepted as complying with the Building Code for the matters covered.

Question 26Legislation, regulations and standards for drainlaying

Under the Building Act 2004, the excavation and installation of a new private drain on the site of a building is classified as which category of building work?

  1. Design work
  2. Demolition
  3. Maintenance
  4. Sitework Correct answer.

Explanation

The Building Act 2004 defines building work broadly and expressly includes sitework, which covers excavation, filling, and the construction of drains and other utility connections on the site of a building. Installing a new drain is therefore building work in the sitework category, which is why a building consent and inspection regime can apply to it.

Question 27Legislation, regulations and standards for drainlaying

Which licence class under the Plumbers, Gasfitters, and Drainlayers Act 2006 authorises a drainlayer to certify their own drainlaying work as compliant?

  1. Registered drainlayer
  2. Apprentice drainlayer
  3. Limited certificate holder
  4. Certifying drainlayer Correct answer.

Explanation

Certification of drainlaying work is reserved for the certifying drainlayer licence class, which is the class that carries the authority to certify completed work. A registered drainlayer is licensed to carry out drainlaying but must have the work certified by a certifying drainlayer or verified by a building consent authority inspection.

Question 28Legislation, regulations and standards for drainlaying

A drainlayer is checking the performance requirements that apply to the disposal of foul water from a new dwelling. Which Building Code clause applies?

  1. Clause G14 Industrial liquid waste
  2. Clause G13 Foul water Correct answer.
  3. Clause G12 Water supply
  4. Clause E1 Surface water

Explanation

Clause G13 of the Building Code sets the objectives and performance requirements for the disposal of foul water from buildings, and drainage work for a dwelling must satisfy it. Related clauses cover different services: E1 deals with surface water, G12 with water supply, and G14 with industrial liquid waste.

Question 29Legislation, regulations and standards for drainlaying

A drainlayer needs the New Zealand standard that sets out design and installation requirements for sanitary plumbing and drainage in buildings. Which standard applies?

  1. NZS 1547
  2. NZS 3604
  3. NZS 3910
  4. AS/NZS 3500.2 Correct answer.

Explanation

AS/NZS 3500.2 is the joint Australian and New Zealand standard for sanitary plumbing and drainage, and it is the technical reference used for drainlaying design and installation in New Zealand. The other documents commonly appear on a drainlayer's reading list but govern different subject matter.

Question 30Legislation, regulations and standards for drainlaying

A territorial authority considers that recently completed drainage work breaches the Building Code and issues a notice to fix. What is the legal effect of that notice?

  1. It requires the breach to be remedied within the stated time Correct answer.
  2. It cancels the building consent with immediate effect from the date of issue
  3. It transfers the work to a certifying drainlayer chosen by the authority
  4. It imposes an infringement fine payable to the territorial authority

Explanation

A notice to fix is an enforcement tool under section 164 of the Building Act 2004. It requires the person named to remedy the contravention of the Act or regulations within the period stated in the notice, and the territorial authority may take further enforcement action if it is not complied with.

Question 31Drainage system design, hydraulics and falls

A foul water drain is laid at a gradient of 1:60. What fall does this produce for every metre of pipe?

  1. 6.0 mm
  2. 16.7 mm Correct answer.
  3. 1.67 mm
  4. 60 mm

Explanation

A gradient of 1:60 means one unit of fall for every 60 units of horizontal length, so per metre the fall is 1000 mm divided by 60, which is 16.7 mm. This is the standard way of converting a ratio grade into a fall per metre for setting out.

Question 32Drainage system design, hydraulics and falls

A drain falls at a gradient of 1:100 over a straight run of 25 m. What is the total fall over that run?

  1. 25 mm
  2. 500 mm
  3. 250 mm Correct answer.
  4. 125 mm

Explanation

Total fall equals run length divided by the gradient denominator: 25 m divided by 100 gives 0.25 m, or 250 mm. Setting out levels always uses the total fall over the run, not the fall per metre.

Question 33Drainage system design, hydraulics and falls

In drainage work, the invert level of a pipe is best described as:

  1. the level of the inside bottom of the pipe Correct answer.
  2. the finished ground level directly above the pipe
  3. the level of the inside top of the pipe
  4. the level of the outside bottom of the pipe

Explanation

The invert is the level of the lowest point of the internal bore of the pipe at a given point. Hydraulic design, gradients and depth of cover are all calculated from invert levels, not from the outside of the pipe.

Question 34Drainage system design, hydraulics and falls

What minimum self-cleansing velocity is normally adopted when designing a foul water drain?

  1. 0.3 m/s
  2. 0.6 m/s Correct answer.
  3. 0.1 m/s
  4. 1.5 m/s

Explanation

A velocity of about 0.6 m/s at design flow is the accepted minimum for keeping solids moving in a foul water drain. Below this, solids settle out and the drain progressively silts up.

Question 35Drainage system design, hydraulics and falls

A drain is described as having backfall when it is laid:

  1. with a fall steeper than 1:20
  2. perfectly level over its full length
  3. with a fall against the direction of flow Correct answer.
  4. with a fall in the direction of flow

Explanation

Backfall is a fall running the wrong way, so that the pipe slopes upwards in the direction of flow. It causes ponding, solids deposition and repeated blockages at the low point.

Question 36Drainage system design, hydraulics and falls

What is the minimum depth of water seal required in a gully trap?

  1. 75 mm
  2. 50 mm Correct answer.
  3. 100 mm
  4. 25 mm

Explanation

Traps must retain a water seal of at least 50 mm to resist the passage of sewer gas. A shallower seal can be lost through evaporation or pressure fluctuations and stop the trap working.

Question 37Drainage system design, hydraulics and falls

Why is a rodding eye or inspection opening installed at the head of a drain run?

  1. to give access for clearing blockages Correct answer.
  2. to vent sewer gas above the roofline
  3. to measure the rate of flow in the drain
  4. to trap debris before it reaches the main drain

Explanation

An access point at the upstream end lets a drainlayer rod or jet the run in the direction of flow. Every drain needs access points positioned so that the whole length can be cleared without removing fittings.

Question 38Drainage system design, hydraulics and falls

Why do plumbing codes limit how steep a foul water drain may be?

  1. Solids are stranded and the pipe scours Correct answer.
  2. Access points become hard to reach
  3. The drain stops being self-cleansing
  4. The pipe loses capacity as grade rises

Explanation

On very steep grades the liquid travels fast while solids are left behind, so the drain silts up, and the high velocity can also scour the pipe wall. Where the ground is steep, energy is usually controlled with a backdrop or a series of drops instead.

Question 39Drainage system design, hydraulics and falls

A drain has a surface cover level of 20.500 m and the pipe invert is 1.350 m below that cover. What is the invert level?

  1. 21.850 m
  2. 19.350 m
  3. 20.350 m
  4. 19.150 m Correct answer.

Explanation

Invert level equals cover level minus the depth to the invert: 20.500 minus 1.350 gives 19.150 m. Depths are always subtracted from the surface level to give the level of the flow line.

Question 40Drainage system design, hydraulics and falls

The invert level at an upstream manhole is 12.400 m. The drain runs 24 m at a gradient of 1:80 to the next manhole. What is the invert level at the downstream manhole?

  1. 12.150 m
  2. 12.700 m
  3. 11.200 m
  4. 12.100 m Correct answer.

Explanation

The fall over the run is 24 m divided by 80, which is 0.300 m. Subtracting that from the upstream invert gives 12.400 minus 0.300, which is 12.100 m.

Question 41Drainage system design, hydraulics and falls

What is the minimum gradient normally required for a 100 mm foul water drain under the New Zealand Building Code?

  1. 1:60 Correct answer.
  2. 1:100
  3. 1:20
  4. 1:40

Explanation

The acceptable solution for foul water drainage sets a minimum grade of 1:60 for a 100 mm drain. That grade is what generates the self-cleansing velocity at typical dwelling flows.

Question 42Drainage system design, hydraulics and falls

A 100 mm diameter drain is flowing full at a velocity of 0.6 m/s. What is the approximate discharge?

  1. 4.7 L/s Correct answer.
  2. 2.4 L/s
  3. 0.5 L/s
  4. 1.2 L/s

Explanation

The full-bore area of a 100 mm pipe is about 0.00785 square metres. Multiplying by 0.6 m/s gives about 0.0047 cubic metres per second, which is 4.7 L/s.

Question 43Drainage system design, hydraulics and falls

A drain is laid at a gradient of 1:80. Expressed as a percentage, this gradient is:

  1. 1.8%
  2. 0.8%
  3. 8.0%
  4. 1.25% Correct answer.

Explanation

A gradient of 1:80 is a fall of 1 unit in 80, which equals 0.0125. Multiplying by 100 gives 1.25%, so the fall is 12.5 mm per metre.

Question 44Drainage system design, hydraulics and falls

Why are foul water drains normally designed to run part-full rather than full at design flow?

  1. To reduce the depth of pipe bedding required
  2. So that flow velocity remains below 0.3 m/s
  3. To stop tree roots entering the pipe joints
  4. To allow air space above the flow Correct answer.

Explanation

Designing for part-full flow leaves an air space above the water surface, which ventilates the drain and gives room for surges without the pipe running under pressure. It also keeps the drain from surcharging back into fixtures.

Question 45Drainage system design, hydraulics and falls

Venting of a sanitary drainage system is primarily provided to:

  1. allow the drain to be rodded from the roof
  2. protect trap water seals from siphonage Correct answer.
  3. reduce the build-up of sewer gas only
  4. increase the velocity of flow in the drain

Explanation

Venting equalises air pressure on both sides of a trap seal so that a slug of water flowing away does not siphon the seal out. Once the seal is lost, sewer gas can enter the building.

Question 46Drainage system design, hydraulics and falls

Stormwater from a dwelling roof is found connected into the foul water drain. What is the correct action?

  1. fit a gully trap at the downpipe base
  2. reduce the roof catchment area
  3. leave it if the drain is 150 mm or larger
  4. disconnect it and pipe it to stormwater Correct answer.

Explanation

Foul water and stormwater must be carried in separate systems, because stormwater flows would overload the foul drain and the treatment system. The roof connection must be removed and the downpipe redirected to the stormwater system.

Question 47Drainage system design, hydraulics and falls

A 100 mm drain has 0.9 m of fall available over a 60 m run. What gradient does this give, and does it meet a 1:60 minimum?

  1. 1:60, which just meets the minimum
  2. 1:67, which does not meet the minimum Correct answer.
  3. 1:75, which does not meet the minimum
  4. 1:54, which meets the minimum

Explanation

The gradient is the run divided by the fall: 60 divided by 0.9 gives about 1:67. Because 1:67 is flatter than the 1:60 minimum, the drain would need a steeper grade or a different alignment.

Question 48Drainage system design, hydraulics and falls

The invert at the top of a drain run is 8.640 m and at the bottom it is 8.280 m over a length of 18 m. What is the gradient?

  1. 1:60
  2. 1:40
  3. 1:72
  4. 1:50 Correct answer.

Explanation

The fall is 8.640 minus 8.280, which is 0.360 m. Dividing the run by the fall gives 18 divided by 0.36, which is 1:50.

Question 49Drainage system design, hydraulics and falls

What is the minimum nominal diameter for a below-ground foul water drain serving a single dwelling?

  1. 50 mm
  2. 65 mm
  3. 100 mm Correct answer.
  4. 150 mm

Explanation

A 100 mm nominal diameter is the minimum permitted for a below-ground foul water drain from a dwelling. Smaller sizes lack the capacity and the self-cleansing performance for soil fixtures.

Question 50Drainage system design, hydraulics and falls

On a steep site a drain arrives at a manhole with an excessively high velocity. What is the usual design solution?

  1. increase the pipe diameter upstream
  2. fit a gully trap at the manhole
  3. reduce the pipe diameter downstream
  4. install a backdrop drop at the manhole Correct answer.

Explanation

A backdrop brings the flow vertically down inside the manhole so that energy is dissipated before the flow continues downstream. This controls velocity without needing an unworkably flat pipe gradient.