NZ Certifying Drainlayer study guide
NZ Certifying Drainlayer · Work through your exam, one topic at a time.
The Certifying Drainlayer is a New Zealand licensing class administered by the Plumbers, Gasfitters and Drainlayers Board. It sits above the standard registered drainlayer class: a certifying drainlayer is authorised to certify that drainage work they have personally carried out complies with the New Zealand Building Code and the cited standards, so that building consent authorities can accept that certification instead of inspecting every element. The NZ Certifying Drainlayer study guide has 9 sections and about 3,155 words.
01Legislation, Regulations and Standards for Drainlaying
Drainlaying in New Zealand is governed by overlapping instruments. The Building Act 2004 makes drainage work "building work", requires building consent unless an exemption in Schedule 1 applies, and imposes the Building Code , whose relevant clauses are G13 (foul water), G14 (industrial liquid waste), G15 (solid waste) and E1 (surface water).
343 words, about 2 min02Drainage System Design, Hydraulics and Falls
Design has three jobs: carry the load, keep the pipe self-cleansing, and protect trap seals. Loads are counted in discharge (fixture) units and converted to pipe size using the AS/NZS 3500.2 tables; the size chosen is then checked against the minimum grade permitted for that diameter.
360 words, about 2 min03Site Assessment, Ground Conditions and Earthworks
A drainlayer reads the site as carefully as the drawings. Establish datum and levels (confirm whether the plan uses NZVD2016, an older national datum or a local authority datum), then check ground conditions : soil type and classification, bearing capacity, groundwater level and its seasonal variation, rock, fill, expansive clays, liquefaction-prone or contaminated ground (HAIL sites), and slope stability.
344 words, about 2 min04Pipe Materials, Components, Jointing and Bedding
Common NZ drainage materials include uPVC (solvent-cement or rubber-ring jointed, the default for building drains and sewer laterals), PE/HDPE (butt-fused or electrofused, good for long runs, rising mains and ground movement), concrete (AS/NZS 4058, large mains and stormwater), vitrified clay (chemically resistant), cast iron (acoustic and above-ground fire-rated situations), and copper and PP for particular above-ground and specialist uses. Each has its own jointing method, bedding class, deflection limits and handling rules.
339 words, about 2 min05Installation of Below-Ground and Above-Ground Drainage
Installation starts with accurate setout: string line or laser, grade checked regularly, invert levels recorded as laid. Trenches are excavated to the designed width and depth, the bed prepared, pipes laid from the low end with sockets upstream, junctions set to the correct angle and orientation, and inspection openings placed so every part of the drain can be rodded.
350 words, about 2 min06Testing, Commissioning and Inspection of Drainage Systems
Inspection is staged: pre-cover inspections by the building consent authority, plus the drainlayer's own checks. Tests available include water (hydrostatic) testing - plug the low end, fill to a nominated head above the highest point of the section, hold for the specified period and check for loss; air testing with a calibrated gauge and a permissible pressure drop; smoke testing to find illegal connections and leaks in existing systems; dye testing to trace connections; CCTV inspection with recorded survey for buried and existing lines; deflection testing with a mandrel for flexible pipe; and, for mains, infiltration/exfiltration or low-pressure air tests under NZS 4404.
342 words, about 2 min07Trade Waste, On-Site Wastewater and Special Drainage Systems
Discharges other than domestic sewage are controlled by the network operator's trade waste bylaw and a discharge consent or permit. The permit sets volume, flow rate, temperature, pH, contaminant limits, pre-treatment requirements, sampling point location and monitoring obligations.
352 words, about 2 min08Plan Interpretation, Documentation and Certification
A drainage set normally includes a site plan, drainage plan, sections and details, plus specifications and consent conditions. Establish the scale , north point, the datum , and whether levels shown are ground level (GL), invert level (IL), obvert or finished floor level (FFL).
353 words, about 2 min09Supervision, Health and Safety, and Contracting Practice
Licensed certifying drainlayers carry responsibility for the work they supervise as well as the work they do. Trainees and limited certificate holders must work under the supervision arrangement and to the standard the Board requires - supervision must be real, with the supervisor able to check and correct the work, and with the trainee's competence matched to the task.
372 words, about 2 min