Hot Water Cylinder Seismic Restraints in Wellington

Quick answer

Yes. Under the Building Code, a storage hot water cylinder has to be held against earthquake movement, and Acceptable Solution G12/AS1 shows how: tensioned galvanised steel straps screwed into the wall framing near the top and bottom of the cylinder. A cylinder held only by its pipes can topple in a quake, flood the house and lose the water you may need afterwards.

A full hot water cylinder is one of the heaviest things in a house, and it usually stands in a cupboard with pipes, power and sometimes gas attached. In a strong shake an unrestrained cylinder can tip, snap its connections and empty itself across the floor.

This guide explains what a proper restraint looks like, how to check yours in five minutes, what a homeowner can and cannot do, and the other plumbing and gas items worth securing before the next quake.

Does my hot water cylinder need a seismic restraint?

Yes. The Building Code requires building elements to be supported against earthquake forces, and Acceptable Solution G12/AS1, which covers water supplies, sets out how storage water heaters should be restrained.

The G12/AS1 method applies to storage water heaters of up to 360 litres in light timber-framed buildings designed to NZS 3604. According to BRANZ, it uses 25 by 1 mm galvanised steel straps, tensioned when fixed, with each end screwed into the wall framing using 8 mm coach screws and washers that reach at least 50 mm into the timber. Depending on the cylinder's size and the strap positions, up to four straps may be needed. Tanks over 360 litres fall outside G12/AS1 and need a specifically designed solution.

Any new cylinder installed today should be restrained to this standard as part of the job. Older installations are worth checking, because G12/AS1 was updated in 2024 to clarify the restraint requirements, and straps that were fitted correctly years ago can loosen or rust.

Why does a restraint matter more in Wellington?

Because the region has about 50 active faults, many capable of damaging earthquakes, according to GNS research. The Wellington Fault runs through Karori and the city and along the Hutt Valley, and a rupture is expected to produce about a magnitude 7.5 earthquake.

Ground conditions add to it. Shaking increases on the deep alluvial floor of the Hutt Valley towards the Petone foreshore, and older studies placed Petone, Seaview and Gracefield among areas with liquefaction potential. A cylinder in a Petone house can be shaken harder than one on firmer ground.

There is also a practical reason. WREMO lists the hot water cylinder as one of the most valuable sources of water after a disaster, and tells households to check it is well secured. A cylinder that falls over loses that water at the moment you need it.

How can I tell if my cylinder is restrained properly?

Open the cupboard and look for metal straps that wrap around the cylinder and fix into the wall behind it, one near the top and one near the bottom. BRANZ guidance places the straps within the top and bottom quarter of the cylinder.

Then run through the checks below. If the answer to any of them is no, the cylinder is not properly restrained.

A plumber can check all of this during routine hot water servicing, along with the valves and element, and tell you what needs fixing before anything is changed.

There are at least two metal straps, near the top and the bottom, not plastic ties or wire
The straps are tight against the cylinder, with no slack when you push it
Each strap end is screwed into a wall stud or nogging, not just plasterboard
The fixings are coach screws with washers, not small nails or panel pins
The straps and screws are free of heavy rust
The cylinder sits flat on a solid base and is not held up by its pipes
Any header tank in the ceiling space is fixed down too

Is your cylinder strapped in?

Cheeky's Plumbers can check your cylinder restraint, valves and connections and fix what needs fixing, with the price agreed first.

0800 758 622 Book Online Get a quote

Can I fit a seismic restraint myself?

You can tighten a loose strap or replace a corroded screw, but fitting a full restraint is best left to a plumber, especially on an older cylinder.

There are three reasons. The straps have to land on solid framing, and in a retrofit BRANZ notes that extra framing may be needed to get adequate fixing; finding studs behind old lath and plaster in a Mt Victoria or Newtown villa is harder than it sounds. A cylinder that has settled may need lifting, levelling or a new base. And if the pipes have to be moved, or the valves turn out to be faulty, that is plumbing work for a licensed plumber.

Never try to move or re-seat a gas water heater yourself. WorkSafe advises having all gasfitting done by a currently licensed gasfitter, who must certify the work.

If your cylinder is old, rusty at the base or already leaking, it often makes more sense to replace it with a new one that is restrained as part of the install. Our hot water cylinders page explains the options.

Do flexible connections help in an earthquake?

They can. Straps stop the cylinder falling, but a strapped cylinder can still move a little, and rigid copper pipes can crack where they join it.

Flexible connectors or a short loop in the pipe let the cylinder shift slightly without tearing the joint. This matters most on the cold water inlet and hot outlet, where a broken joint will keep pouring until someone turns the water off at the toby. On a gas cylinder, the gas connection must be done to the appliance maker's instructions by a licensed gasfitter.

Flexible hoses are not a fit-and-forget part. Braided hoses age, and a corroded or kinked hose is a leak waiting to happen, so have them checked when the cylinder is serviced.

What about gas hot water and LPG bottles?

Gas adds a fire risk to a quake, so know where to turn the gas off and make sure bottles cannot fall.

If your hot water runs on natural gas, find the isolation valve at the gas meter now, while things are calm. If you smell gas after a quake, leave the house, do not use light switches or anything that can spark, turn off the supply at the meter if it is safe to do so, and call the Powerco gas emergency line on 0800 111 848 from outside.

Outdoor LPG bottles should stand on a firm base and be chained or strapped to the wall so they cannot tip and stress the regulator and pipe. A licensed gasfitter can check the installation, the fixings and the shut-off, which is part of our gas fitting service.

What else in the house should be secured for a quake?

Anything heavy that holds water or gas, or that is tall enough to fall: the header tank, a wall-hung continuous flow unit, rainwater and emergency tanks, and LPG bottles.

Inside, check that the washing machine is not walking on its hoses, that the toby is easy to reach and turn, and that everyone in the house knows where it is. In hillside Hataitai, where many homes date from the early 1900s to the 1950s and pipework is ageing, it is also worth looking under the house for pipes resting on loose packers rather than clipped to the framing.

If you want it all checked in one visit, Cheeky's Plumbers can go through the cylinder, valves, gas and toby and give you a fixed price for anything that needs doing. Our plumber Eastern and Southern Suburbs page covers Hataitai, Kilbirnie, Miramar and the south coast, or you can book online.

Frequently Asked Questions

Are plumber's strap kits from a hardware store good enough?

A kit can work if it uses galvanised steel straps of the right size and the fixings go into solid framing. Plastic straps, wire or screws into plasterboard alone will not hold a full cylinder in a strong quake.

Does a heat pump water heater need restraining?

Yes. Any storage water heater, whether electric, gas or heat pump, holds a heavy tank of water and should be restrained. Follow the maker's NZ installation instructions as well as G12/AS1.

Will insurance pay if an unrestrained cylinder floods the house?

That depends on your policy. Some insurers may ask whether the cylinder was installed to the Building Code, so keeping it properly restrained avoids an argument later.

How often should I check the cylinder straps?

A quick look once a year is enough, and again after any noticeable earthquake. Check that the straps are still tight, the screws are firm and nothing is rusting through.

Does a restraint stop the cylinder leaking in a quake?

It stops the cylinder falling, which is the main cause of broken connections. Flexible connections and good valves reduce the risk of a joint failing as well.