Overheating Homes in NZ Summer 2026: How to Cool a Hot Townhouse Now Building Code Rules Are Delayed to 2031

If your upstairs bedroom hit the mid-30s last February, you're not imagining it and you're not alone. On 28 September, MBIE confirmed that overheating won't be in the 2028 Building Code review. It has been pushed out to the 2031 review. That means no new rules for at least five years, and nothing that would ever apply retrospectively to the home you already live in.

So the fix is on you. This article explains why so many newer NZ townhouses and apartments overheat, which fixes actually work (and in what order), what they cost to run at today's power prices, and the one ventilation mistake that can make a hot house hotter.

At a Glance

• The rules aren't coming soon. MBIE says overheating needs "considerable technical and policy work", so it has moved from the 2028 Building Code review to 2031.
• It's a widespread problem. BRANZ data from summer 2023/24 found 70% of people said their home was warmer than they wanted at least some of the time.
• Stop the sun first. External shading on west- and north-facing glass does more than anything else you can buy, and it costs nothing to run.
• Flush heat out at night. Cross-ventilation and night purging are free. A well-set ventilation system can help, but a positive-pressure system pulling from a 45°C roof space will make things worse.
• Fans are the cheapest comfort. A ceiling fan costs around 1–3 cents an hour to run at NZ's average power price of about 39c/kWh.
• A heat pump is the backstop. Cooling a lounge with a 5 kW split costs up to about 45–55 cents an hour at full output (less once the room is cool), and you get winter heating from the same unit.

Why MBIE's delay matters to you

The story, reported by RNZ and 1News on 28 September 2026, centres on the glut of townhouses and apartments built in the last few years. An Auckland resident described upstairs temperatures of 35°C during the day, still in the high 20s late in the evening, and an aluminium front door too hot to touch.

MBIE's manager for building performance and engineering, Dave Gittings, said the issue is complex and interconnected. The NZ Green Building Council's chief executive, Andrew Eagles, said the council was "really shocked" by the delay. BRANZ has been flagging the problem for years.

For homeowners the practical upshot is simple. The Building Code currently has detailed rules on keeping heat in (the H1 insulation changes taking effect on 26 November are the latest, and we cover them in our H1 insulation explainer). It has nothing equivalent on keeping excess heat out. Better-insulated, more airtight homes hold onto heat in winter, and in summer they hold onto it too, unless the design lets it escape.

Even when rules do arrive in the 2030s, they'll apply to new consents. If you own or rent a 2018–2025 townhouse, nobody is coming to retrofit it for you.

Why newer NZ townhouses overheat

It's mostly design, not insulation. The common culprits named by BRANZ and the Green Building Council:

• Large areas of glass, especially floor-to-ceiling glazing on west or north faces. Glass lets sunshine in as heat, and it doesn't leave the same way.
• No eaves or external shading. Older NZ houses often had generous eaves that blocked high summer sun. Many new builds have none.
• Limited cross-ventilation. Terraced and attached homes have fewer external walls, so there's often no way to get a breeze flowing through from one side to the other.
• Dark roofs and tight spacing. Dark cladding absorbs heat, and buildings packed close together reflect it at each other.
• Heat rises. In a three-storey townhouse the top floor, usually the bedrooms, collects heat from the whole building.

Knowing which of these applies to your home tells you which fix will pay off.

The fixes, in the order that makes sense

1. Block the sun before it hits the glass

This is the single most effective thing you can do. Shading outside the window stops the heat before it enters. Internal blinds and curtains help, but by the time sunlight reaches them it's already inside, and much of that heat stays in the room.

Options, roughly from cheapest to most expensive:

For apartments and many townhouses, external changes may need body corporate approval or affect your weathertightness warranty. Ask before you drill.

2. Get the heat out at night (night purging)

NZ summer nights are usually much cooler than the days, even in Auckland. Night purging means opening the house up after sunset to let cooler air flush out the heat stored in floors, walls and furniture, then shutting it up again by mid-morning, before the outdoor air warms past the indoor temperature.

• Open windows on opposite sides or different levels to get air moving. In a multi-storey townhouse, a low window downstairs and a high window upstairs use the stack effect: warm air leaves at the top and pulls cooler air in at the bottom.
• Security stays and restricted-opening window catches let you leave windows ajar overnight more safely.
• A box fan facing out of an upstairs window will push hot air out and draw cooler air in through the rest of the house.

It costs nothing, and in many homes it's the difference between a 29°C bedroom at 11pm and a 23°C one.

3. Check what your ventilation system is doing in summer

This is where a lot of NZ homes go wrong. Ventilation systems fall into two main camps, which we compare in detail in positive pressure vs balanced ventilation.

Positive-pressure systems (the common roof-mounted units marketed under brands like HRV, DVS and Smartvent) push air from your roof space into the house. In winter that roof air is useful because it's relatively dry. On a sunny summer afternoon, though, a roof cavity under dark roofing can be far hotter than your living room, often 40°C or more.

Many current units have a roof-space temperature sensor that should stop them supplying air when it's hotter than inside, and some offer a summer kit or alternative intake that draws outdoor air instead. Older units, or units that have never been set up, may not. Check:

• Is the controller on a summer setting? Many systems have seasonal modes, and installers sometimes leave them on the winter profile for years. We cover this in our HRV, DVS and Smartvent running costs piece.
• Does the system have a summer intake or bypass option, and is it fitted?
• Put your hand under a ceiling grille at 3pm on a hot day. If the air feels warmer than the room, the system is heating your house. Turn it off during the day or ask your installer to adjust it.

Balanced systems with heat recovery supply and extract air in equal measure. A good one has a summer bypass that routes air around the heat exchanger when the outside air is cooler than inside, typically overnight, so you get filtered night purging without opening windows. BRANZ recommends housewide mechanical ventilation combined with reasonable airtightness for new builds and major renovations, and it's a big part of why balanced systems are increasingly specified in new homes.

If you're choosing a system now, ask the installer directly how it behaves on a 30°C afternoon. That's as important as how it handles winter condensation. Our complete home ventilation guide covers the system types and costs in more detail.

4. Add ceiling fans (the cheapest comfort per dollar)

Fans don't lower the air temperature, but moving air across your skin makes a room feel several degrees cooler. A ceiling fan draws roughly 30–75W on typical settings, which at an average NZ price of about 39c/kWh (MBIE's February 2026 survey) works out to around 1–3 cents an hour. Pedestal fans are similar.

A ceiling fan installed by an electrician typically costs a few hundred dollars per room including the unit. For upstairs bedrooms, this is usually the best value upgrade on this list.

5. Use a heat pump for cooling (the backstop)

Every reverse-cycle heat pump sold in NZ also cools, and if your home simply can't shed enough heat passively, this is the reliable fix. As a rough guide at around 39c/kWh:

These are full-output figures, assuming the unit is working at a typical efficiency, delivering three to four units of cooling for each unit of electricity. In practice it will often cycle down once the room reaches temperature, so real hourly costs are frequently lower. Running a 5 kW lounge unit for five hours on a hot evening costs around $2–$3. That's not nothing over a long summer, but it's far less than most people expect.

Some tips to keep the cost down:

• Set it to 24–25°C, not 18°C. Each degree cooler adds to the running cost, and 24°C feels cool when you've come in from 30°C.
• Shade and purge first. A heat pump fighting direct afternoon sun through west-facing glass works much harder than one maintaining a shaded room.
• Use "dry" mode on humid days. In Auckland and Northland humidity is often the real discomfort, and dry mode removes moisture while using less energy than full cooling.
• Shift the hours if you're on a time-of-use plan. Pre-cool the bedroom in the off-peak afternoon window if your plan has one, rather than cranking it at the evening peak. Our guide to running a heat pump on time-of-use power covers how the 2026 tariffs work.

Installed, a single-room high-wall split typically runs $2,000–$6,000 depending on size and how tricky the install is. In a townhouse, check early where the outdoor unit can legally and practically go, because body corporates and boundary setbacks often decide this for you. For winter running costs on the same unit, see heat pump running costs in NZ winter 2026.

A note on subsidies: Warmer Kiwi Homes funding is for heating in eligible owner-occupied homes. There is no government grant for cooling or shading. If you qualify for a heat pump subsidy for heating, the unit will cool too, but cooling isn't the reason it's funded. You can check your eligibility for heating and insulation grants.

If you rent

Renters can't install external blinds or a heat pump without permission, but they can:

• Night purge, and use pedestal or box fans (a box fan facing out of an upstairs window works well).
• Use removable reflective film or covers and block-out curtains on the worst windows.
• Check and adjust any ventilation system controller, and tell the landlord if the system is blowing hot air in summer.
• Ask the landlord for a heat pump. The Healthy Homes Standards already require a fixed heater in the main living room, and that is often a heat pump, so many rentals already have the cooling capability.

What to do before summer

October and November are the right time to sort this out, before installers book up and the first hot spell arrives.

1. Map the hot rooms. Note which rooms are worst and at what time of day. West-facing rooms in the late afternoon point to shading. Top-floor bedrooms at night point to purging, fans and possibly a heat pump.
2. Check your ventilation system's summer settings this week. It's free and takes five minutes.
3. Fix the sun first, at least on the worst one or two windows.
4. Add fans to the bedrooms that stay hot at night.
5. Get heat pump quotes if the house still won't cool down. Ask about outdoor unit placement and the noise rating, since you'll be running it at night near neighbours.

Not sure where to start? Take our free home assessment for a prioritised list of upgrades for your home, or find ventilation and heat pump installers in your area and get quotes in before the summer rush.