New Drainlaying in Christchurch: Consents, Council Rules and Ground Conditions

Do you need a building consent?

Most new drainage work connecting to the public network, or any drainage that's part of a new dwelling, minor dwelling or major renovation, needs a building consent through Christchurch City Council, Selwyn District Council or Waimakariri District Council depending on where the property sits.

The drainage plan has to show pipe sizes, falls, inspection points and the connection point to the council main. As-built plans are required once the work is finished, showing exactly what was laid and where.

Connecting to the council network

• A council-issued point of connection for both wastewater and stormwater
• Correct separation between wastewater and stormwater lines, they must never be combined
• Inspection chambers at every junction and change of direction
• A pre-cover inspection by council before the trench is backfilled

Ground conditions after the earthquakes

Ground conditions vary a lot across Canterbury. Parts of eastern Christchurch and the Avon Loop still have soft, silty ground affected by liquefaction, which means trenches need more careful backfill and compaction to stop the new pipe settling unevenly later.

On the Port Hills and Banks Peninsula, rock and hard clay can mean a digger with a breaker attachment rather than a standard trencher, which changes both timeframe and cost. In Selwyn and Waimakariri's newer subdivisions, ground is usually more predictable, though shallow water tables in some areas need dewatering before pipe can go in.

Materials we use

• PVC pipe for gravity wastewater and stormwater, now standard for new work
• Class SN pipe rated for the expected ground loading and depth
• Sealed rubber-ring joints rather than solvent weld on longer runs, to allow for minor ground movement
• uPVC or concrete inspection chambers depending on depth and council specification

Falls and gravity

Every gravity drain needs enough fall to keep waste moving without running so fast that solids get left behind. We set this out before digging starts and check it with a laser level as the pipe goes in, because a flat or reversed section is one of the most common causes of a blocked new drain.

What the process looks like

• Site visit and drainage plan drawn up
• Building consent lodged with the relevant council
• Trenching and pipe laid to the approved plan
• Pre-cover inspection booked with council before backfill
• As-built plan submitted and code compliance certificate issued

Working around existing services

Older Christchurch sections often have services in unexpected places from past repairs or earthquake remediation. We run a locate before digging and adjust the route if needed, which is far cheaper than striking an unmarked line halfway through the job.

Frequently asked questions