Frozen pipes might seem like a problem only for Canadian winters, but in New Zealand — particularly in Otago, Southland, Canterbury, Central Plateau, and elevated parts of the North Island — overnight temperatures regularly drop well below zero. When water freezes inside a pipe, it expands, and that pressure can split copper, crack plastic fittings, or blow joints apart, leading to costly water damage. The good news is that a few simple precautions can keep your plumbing flowing all winter long.
Why Pipes Freeze (and Why It Matters)
Water expands by roughly 9% when it freezes. In a sealed pipe, that expansion has nowhere to go, so pressure builds until something gives way. The burst often doesn't show itself until the ice thaws — then water pours out. Pipes most at risk are those in unheated spaces: under the house (sub-floor), in roof cavities, in garages, in exposed outdoor areas, and anywhere that gets little or no insulation. Older NZ homes with timber piles and open sub-floors are especially vulnerable.
Insulate Exposed Pipes First
Pipe lagging (foam insulation sleeves) is your first and most cost-effective defence. It's available from Bunnings and Mitre 10 in various diameters to suit standard copper and CPVC pipe sizes.
- Measure the outside diameter of your pipes before you shop.
- Cut lagging with a sharp knife and use waterproof tape or cable ties to secure joins.
- Pay special attention to bends, T-junctions, and valve bodies — these are easy to miss.
- For outdoor taps (hose taps), purpose-made tap covers or a simple wrap of pipe lagging secured with tape works well.
- In roof spaces, make sure lagging is also protected from moisture — wet insulation loses most of its effectiveness.
BRANZ research confirms that sub-floor and roof-space insulation improves overall home warmth, which indirectly helps protect pipes in those areas too.
Seal Draughts Around Pipes
Cold air rushing through gaps in the sub-floor or exterior walls can freeze pipes even when the surrounding insulation seems adequate. Use expanding foam or flexible sealant (products from Sika are widely available) to seal penetrations where pipes pass through exterior framing, foundations, or cladding. This also helps with your home's overall energy efficiency — a win-win.
Keep a Trickle Running on Very Cold Nights
If a severe frost is forecast and you're worried about a particular pipe run, letting a slow trickle of water run from the tap overnight keeps water moving and dramatically reduces the chance of freezing. It wastes a small amount of water, but far less than dealing with a burst pipe. This is a good short-term measure for holiday homes or when you're away.
Drain Down Outdoor and Holiday Home Plumbing
For bach or holiday home owners who leave the property unoccupied over winter, the safest option is to drain the entire system:
- Turn off the water at the toby (main stopcock) — usually at the boundary or under the floor.
- Open all taps (hot and cold) to let water drain out.
- Flush toilets to empty cisterns.
- If you have a hot water cylinder, consider whether it needs draining too — check the manufacturer's instructions.
- Leave taps slightly open so any residual water can escape as it freezes.
Know where your toby is before winter arrives. If you can't locate it, a licensed plumber can find and service it for you.
Hot Water Cylinders and Heat Pumps
Most mains-pressure and low-pressure hot water cylinders in NZ are installed indoors and are not at significant freeze risk themselves, but the pipes feeding and leaving them can be. Check that any pipework in unheated areas near the cylinder is lagged. Heat pump water heaters with outdoor units should be checked against the manufacturer's cold-weather guidance — some have a minimum operating temperature.
For home heating that indirectly keeps pipes warmer, Energywise has good guidance on cost-effective heating options.
Comparison: Freeze-Prevention Methods
| Method | Cost (as a guide) | DIY Friendly? | Best For |
|---|---|---|---|
| Pipe lagging/foam sleeves | Low (a few dollars per metre) | Yes | Sub-floor, roof space, outdoor pipes |
| Tap covers | Very low | Yes | Outdoor hose taps |
| Draught sealing | Low | Yes | Pipe penetrations in exterior walls |
| Trickle flow overnight | Minimal water cost | Yes | Short-term, severe frost nights |
| Draining the system | Free (DIY) | Yes, mostly | Holiday homes, long absences |
| Trace heating cable | Moderate | Possible | High-risk exposed runs |
| Professional re-routing | Higher | No | Pipes in very exposed locations |
When to Call a Professional
Some freeze-prevention work is straightforward DIY, but there are situations where you should call a licensed plumber:
- A pipe has already burst. Turn off the toby immediately, then call a plumber. Water damage escalates fast.
- You can't locate or operate your toby. A plumber can service or replace it.
- Pipes are in very difficult locations — inside concrete slabs, inside walls, or in areas requiring significant access work.
- Installing trace heating cable on pipes near electrical connections — this overlaps with electrical work and may require both a plumber and a registered electrician (see EWRB for what counts as restricted electrical work).
- Any work on gas lines — always a job for a licensed gasfitter registered with the Plumbers, Gasfitters and Drainlayers Board.
For burst pipes especially, acting quickly and having a trusted local tradesperson on call makes a real difference. You can find licensed plumbers in your area at tradedirectory.co.nz.