A Sydenham villa off Colombo Street, July 2022: the gully trap outside the laundry was lifting its grate every time the washing machine emptied. The owner had had the drain “cleared” three times in two years at NZ$180 a visit; nobody had put a camera down it. When we did, the picture showed fine roots at the fourth joint from the gully, a heavier mass at the sixth, and behind that a joint displaced by about 15 mm where the earthenware had settled into 2011 liquefaction. The tree was a silver birch on the neighbour’s side of the fence, 6 metres from the line. Three clearances had bought eighteen months and a false sense the problem was small.
Reading the symptoms before anyone digs
Root intrusion has a signature, not the same as a fat blockage or a collapsed pipe.
- It is seasonal. Roots grow fastest in spring; a lateral that runs fine through winter and slows in November is probably roots.
- It recurs on a rhythm. A drain that blocks every twelve to eighteen months and clears cheaply each time is roots regrowing. A collapsed pipe does not come and go.
- It is progressive. First the toilet flushes slowly, then the gully trap surcharges under load, then overflows. Roots narrow the pipe in stages.
- Paper comes back up but water eventually goes down. A root mat is a strainer, not a plug.
None of that tells you where the roots are or how they got in. That takes a camera.
What the camera has to show you
A drain camera inspection on a residential lateral costs NZ$250 to NZ$450 in Christchurch; the recording is worth more than the visit. Insist on seeing it and on having the operator locate the problem from the surface with a sonde. From the footage, you want four things.
- Pipe material and joint spacing. Glazed earthenware in 600 mm lengths is pre-1970s and full of entry points; concrete is similar. PVC with joints every 6 metres offers roots very little unless a joint has separated.
- How the roots are getting in. Fine hairs at a joint mean the joint is leaking but the pipe is otherwise sound; a root the thickness of a thumb means the gap is larger than it should be; roots through the barrel mean a crack. Each gets a different repair.
- Grade and displacement. Standing water in the picture means a belly or a dropped joint. Roots love a belly because it holds water between flushes. Post-earthquake settlement has left bellies throughout the eastern suburbs in laterals that never had them; roots find them within two or three seasons.
- Distance from the tree. Measure along the pipe from the gully to the ingress point, mark it on the surface, then look up. The nearest large tree is usually the culprit; willow, poplar and birch will travel 20 metres or more to a leaking joint.
The options, priced honestly
Cut and jet. A mechanical root cutter followed by water jetting clears the pipe for NZ$350 to NZ$700, buying six to eighteen months. A foaming herbicide at NZ$300 to NZ$600 slows regrowth for a year or two. Neither fixes the entry point.
Reline. A cured-in-place liner seals joints and cracks along the run without a trench, at roughly NZ$500 to NZ$1,000 per metre. Good where the pipe is straight and holding its shape; not possible where a joint is badly displaced or the pipe has bellied.
Replace the section. Two or three metres near the surface might be NZ$1,800 to NZ$3,500; a full 12-metre lateral at 1.2 metres deep with a new connection and council inspection is NZ$5,000 to NZ$11,000. The section owner owns the lateral to the council main; this bill is yours whatever tree caused it.
Deal with the tree. Removal alone does not fix the pipe; a dead root system leaves voids around a pipe that has already moved. Root pruning under an arborist’s direction, or a barrier between tree and pipe, is often enough where the pipe is being renewed. The same roots often lift a driveway or path above the pipe and the two problems are best handled in one excavation, as the sequence in a Dunedin driveway lifted by roots shows.
Who is allowed to do the work
Sanitary drainage in New Zealand is restricted work. Anyone laying or repairing a sewer lateral must be an authorised drainlayer; like-for-like repair is usually exempt from building consent, but cases that still need it are set out on the Ministry of Business, Innovation and Employment’s building site. Camera inspections and jetting are not restricted, which is why repeated clearances with no lasting fix is a common story. Ask who will sign off before the digger arrives.
Frequently asked questions
How do I know if tree roots are in my sewer? Recurring blockages at roughly yearly intervals, a gully trap that surcharges under load, and drains that slow in spring are the classic pattern. A camera inspection costing NZ$250 to NZ$450 confirms it and shows the entry point.
Will root killer alone fix roots in a drain? No. Foaming herbicide kills roots inside the pipe and slows regrowth for a year or two, but the joint or crack they came through is still open. It is a maintenance step, not a repair.
Can I make my neighbour pay for roots in my lateral? Rarely. You own the lateral and its repair; the tree owner is only liable where the tree is clearly the cause and they were told and did nothing. Dated camera footage and a written notice are what you need if it ever comes to that.