Installing a new gas line to your home involves two distinct phases: the physical trenching work, and the actual gas pipework. In New Zealand, all gas fitting work is restricted work that must be carried out by a licensed gasfitter — but as a homeowner, you may be able to dig the trench yourself and save on labour costs. Read on to understand exactly what you can do, what the rules are, and how to do it safely.
Understand What Is and Isn't DIY Work
Before you pick up a spade, it's important to be clear on the legal boundaries. Under New Zealand law, connecting, installing, or modifying any gas piping is restricted work that must only be performed by a gasfitter registered with the Plumbers, Gasfitters and Drainlayers Board (PGDB). This includes laying the gas pipe itself, making connections, and pressure-testing the line.
What you can typically do as a homeowner is prepare the trench — the physical excavation — before the gasfitter arrives. However, always confirm this with your gasfitter and your local council before starting, as site-specific conditions or consent requirements may affect what's permitted.
Check Whether You Need a Building Consent
In many cases, running a new gas line to a home will require a building consent. Some minor work may fall under Schedule 1 exemptions of the Building Act 2004, but this depends on the scope of work and your local council's interpretation. Always check with your council before starting. Your licensed gasfitter will also be familiar with consent requirements and can advise you. More information on consents is available from MBIE Building Performance.
Call Before You Dig — Locate Underground Services
This is the single most important step before any excavation. New Zealand has underground electricity cables, water mains, telecommunications lines, and existing gas pipes that are not always where you'd expect them.
- Contact Dial Before You Dig (0800 248 344) or visit their website to request a service location for your property.
- Your local council or network utility operator may also be able to provide plans.
- Consider hiring a cable and pipe locator service for added confidence — many excavation contractors offer this.
Striking a live gas main or power cable is extremely dangerous and potentially fatal. Never skip this step.
Trench Depth and Width Requirements
The required trench depth for a residential gas line in New Zealand is generally governed by the gas network operator's specifications and relevant standards. As a general guide:
| Location | Typical Minimum Cover Over Pipe |
|---|---|
| Under garden/lawn areas | 375–450 mm |
| Under driveways or paved areas | 450–600 mm |
| Under buildings | Not generally permitted without specific design |
These figures are a guide only. Your licensed gasfitter and the gas network operator (such as Vector or First Gas, depending on your region) will specify the exact requirements for your installation. Always follow their instructions.
Trench width should be sufficient to allow the pipe to be laid comfortably and bedded correctly — typically around 300 mm wide for a residential supply, but confirm with your gasfitter.
How to Dig the Trench
Planning the Route
- Plan the shortest practical route from the gas meter (or connection point) to the entry point of your home.
- Avoid routes under concrete foundations, large tree root zones, or areas prone to flooding.
- Mark the route clearly with spray paint or string line before digging.
Hand Digging vs. Hiring an Excavator
For short runs in soft soil, hand digging with a spade and mattock is feasible. For longer runs, rocky ground, or clay-heavy soil (common in many parts of NZ), hiring a mini excavator is far more practical and time-efficient. You can find qualified local excavation contractors on tradedirectory.co.nz who can handle the trenching for you.
Digging Tips
- Dig carefully and slowly, especially near the depth where other services may run.
- Keep excavated soil to one side so it doesn't fall back in.
- If you encounter unexpected pipes, cables, or unusual materials, stop digging and seek advice before continuing.
- In wet conditions, trench walls can collapse — shore up the sides if needed, particularly in deeper trenches (WorkSafe NZ has guidance on excavation safety).
Bedding the Trench
Once the trench is at the correct depth, the bottom should be free of sharp rocks or debris. Your gasfitter will typically specify a sand bedding layer (often around 75–100 mm) beneath the pipe to protect it from damage. Have the appropriate bedding sand on hand, or ask your gasfitter what they require. Suppliers like Bunnings or PlaceMakers stock suitable bedding sand.
After the Trench Is Dug
Once your trench is ready, contact your licensed gasfitter to lay the pipe, make all connections, and carry out pressure testing. Do not backfill the trench until the gasfitter has inspected the pipe installation and given you the go-ahead. Backfilling before inspection may mean you have to re-excavate.
After approval, backfill in layers, compacting as you go, and reinstate any landscaping or paving.
When to Call a Professional
All gas pipe installation, connection, and testing must be done by a gasfitter licensed with the PGDB — this is non-negotiable under NZ law. If you're unsure about any aspect of the trenching, encounter unexpected ground conditions, or simply want the whole job handled professionally, a qualified excavation contractor and licensed gasfitter working together is the safest and most efficient approach. Find trusted local tradespeople at tradedirectory.co.nz.
Safety note: Never attempt to connect, modify, or test gas pipework yourself. Gas leaks can cause fires, explosions, and carbon monoxide poisoning. If you ever smell gas, leave the area immediately and call your gas network operator's emergency line.
Sources & Further Reading
- Plumbers, Gasfitters and Drainlayers Board (PGDB) — licensing requirements for gas work
- MBIE Building Performance — building consents and the NZ Building Code
- WorkSafe NZ — excavation and trench safety guidance
- BRANZ — building research and best practice guidance
- Energywise — energy use and home efficiency information
Licensed Building Practitioner (LBP)
