It is a specific kind of misery. Nine o’clock on a February evening, the sun went down an hour ago, and the upstairs bedroom of your two-year-old townhouse is still sitting at 27 degrees. Downstairs is fine. Open a window and you get street noise and no breeze. The house that was so easy to heat in July has become genuinely hard to live in.

If that sounds familiar, you are not imagining it, and it is not just you. New Zealand’s biggest study of indoor temperatures in twenty years has confirmed the problem, and townhouses are among the worst affected. Here is what the research actually says, why it happens in Auckland specifically, and what fixes it — starting with the changes that cost nothing.

The evidence: New Zealand homes really are getting hotter inside

BRANZ has been running the Household Energy End-use Project 2 (HEEP2), the most comprehensive study of indoor conditions in New Zealand homes since the early 2000s. Its summer monitoring makes uncomfortable reading.

What BRANZ measured Finding
Average evening temperatures Exceeded 24°C in both living rooms and bedrooms across the monitored homes.
Bedrooms classed as overheating 36% of the 310 bedrooms monitored, using the CIBSE 1b benchmark — above 26°C for more than 1% of night-time hours.
Households feeling too warm Around 70% said their home felt warmer than they would like at least some of the time in summer (48% sometimes, 22% always or often).
Change over 20 years Indoor summer temperatures up 1.3–2.1°C, a 6–10% rise, against outdoor temperatures rising 4–8% over the same period.

Source: BRANZ, HEEP2 summer monitoring — 151 homes monitored over summer 2023/24, survey data from 425 households.

Read the last row again. More New Zealanders now report being too hot in summer than too cold in winter. That is a genuine reversal, and it has happened quietly while everyone was focused on making homes warmer.

The research is national rather than Auckland-specific, but both BRANZ and the New Zealand Green Building Council single out recently built townhouses and apartments as the buildings where the problem shows up worst. In Auckland that matters more than anywhere else — roughly 16,000 new homes were consented across the region in the year to early 2026, and townhouses and other attached dwellings are driving nearly all of that growth.

Why townhouses overheat: five things stacking up at once

No single design decision causes this. It is five things compounding, and Auckland townhouses tend to have all five.

1. Too much glass, facing the wrong way

This is the big one. Dr Nigel Isaacs of Victoria University of Wellington, commenting on the HEEP2 findings, put summer overheating down to aspects of design and increased glazing, made worse by a poor understanding of how the whole building performs. Modern townhouses are sold on light and openness, which means large windows. When those windows face west, they take the full force of the afternoon sun for three or four hours — exactly when the day is already at its hottest.

2. Narrow floorplates with windows on one or two sides only

A terraced townhouse shares walls with its neighbours. That leaves windows at the front and back and nowhere else, so there is no way to set up a cross-breeze. In a standalone villa you open windows on opposite sides and the house flushes itself out. In a mid-terrace unit, opening both ends often achieves very little, because there is no pressure difference to drive air through.

3. Heat rises, and bedrooms are upstairs

Almost every Auckland townhouse puts living areas downstairs and bedrooms up. Warm air collects at the top of the building through the day, and the upper floor also takes the most heat through the roof. By evening the bedrooms are the hottest rooms in the house — at precisely the moment you need them to be the coolest.

4. The house is very good at holding heat in

Tighter insulation and airtightness requirements have made new builds far better at keeping heat where it is. That is exactly what you want in July. In February the same quality works against you: heat that gets in through the glazing during the day has no easy way back out at night.

It is worth being clear about this, because the point is often mangled: insulation is not the problem. Insulation slows heat moving in both directions and also helps keep afternoon heat out. The problem is heat getting in through glass and having no route out. The HEEP2 Christchurch sub-study found homes built above code actually coped with summer extremes better than code-minimum homes — better building performs better in both seasons.

5. Small volume, ordinary heat sources

A compact townhouse has less air in it to absorb heat. An oven running at 5pm, a dryer, a west-facing TV wall, three people and a laptop each add up faster in 90 square metres than they would in a rambling 1960s bungalow.

The Building Code does not currently check for this

Here is the part most buyers do not know. New Zealand does not require an overheating assessment at the design stage. A townhouse can be consented, built and sold without anyone modelling how hot it will get in February.

The Green Building Council has been pushing for that check for years, pointing out that it is standard practice across much of the OECD, including Australia, and is not technically difficult. Overheating is expected to feature in the current review of energy efficiency requirements. As Otago researcher Helen Viggers put it, the Building Code describes the poorest quality housing it is legal to build — meeting it is a floor, not a standard of comfort.

Until that changes, the fix falls to the owner. The good news is that quite a lot can be done.

What actually fixes it, cheapest first

Work down this list in order. Plenty of Auckland townhouses get most of the way there on the first two rows.

Fix Cost How much it helps
Close blinds and curtains on the sunny side before the room heats up, not after Free Moderate. Timing is everything — once the heat is in, curtains hold it in.
Night purge: open up when the outside air drops below the inside temperature, and shut everything by mid-morning Free Significant, if you can open windows securely. This is the single most effective free change.
Shift heat-generating activities — oven, dryer — out of the late afternoon Free Small but real in a compact townhouse.
External shading: awnings, external blinds, shade sails, deciduous planting $$ High. Stopping sun before it hits the glass beats any internal blind.
Solar control film or low-E glazing on west-facing windows $$ Moderate to high on the worst-affected rooms.
Ceiling or pedestal fans in bedrooms $ Moderate. Moving air feels 2–3°C cooler without changing the temperature.
Heat pump running in cooling mode, correctly sized for the room $$$ High, and the only option that guarantees a set temperature.
Ducted system with zoning, or a multi-split serving the bedrooms $$$$ Highest. Solves the upstairs problem properly rather than room by room.

When cooling is the right answer — and how to get it right

Most Auckland townhouses already have a heat pump. The catch is that it is usually a single high-wall unit in the open-plan living area downstairs, sized for winter heating in that room. It will never cool the bedrooms above it, because you are asking cold air to travel upstairs against its own nature. This is the most common complaint we hear, and it is a design problem rather than a fault — sizing and placement were done for the wrong season.

There are three sensible ways to solve the upstairs problem:

  • Multi-split systems — one outdoor unit serving several indoor heads, so each bedroom gets its own control without a row of outdoor boxes on the wall. Usually the most practical retrofit for a townhouse with no roof space to speak of. See multi-split options.
  • Ducted with zoning — the tidiest result if there is ceiling space, and zoning means you cool the bedrooms at night without paying to cool an empty lounge. A ducted zone controller is what makes this economical rather than extravagant.
  • Mechanical ventilation — genuinely useful for night purging where opening windows is not safe or practical, particularly for ground-floor bedrooms or units fronting a busy road. Be careful with system choice though: a positive-pressure system drawing from the roof cavity can make a hot afternoon worse, because roof cavity air in summer is hotter than the air in your house. Look for summer bypass and temperature sensing. Compare ventilation systems.

If you are unsure which of the three suits your place, our guide to ducted versus split versus cassette systems walks through the trade-offs in more detail.

Frequently asked questions

What indoor temperature counts as overheating?

The benchmark BRANZ used is the CIBSE 1b criterion: a bedroom is overheating if it exceeds 26°C for more than 1% of night-time hours between 10pm and 7am across a year. As a practical rule, if your bedroom is still above 26°C at bedtime, sleep quality suffers — and on that measure 36% of the bedrooms BRANZ monitored were overheating.

Why is upstairs so much hotter than downstairs in my townhouse?

Three reasons at once. Warm air naturally rises and collects on the top floor, the upper storey absorbs the most heat through the roof, and your heat pump is almost certainly downstairs — so the cooled air stays where it is generated. Nothing is broken; the system simply was not designed to cool the upper floor.

Is my townhouse too hot because it is too well insulated?

No, and this is a common misreading. Insulation slows heat transfer in both directions, so it also helps keep afternoon heat out. The real problem is solar heat coming in through glazing with no path back out. BRANZ found homes built above code handled summer extremes better than code-minimum homes, not worse.

Do I need a heat pump in every bedroom?

Usually not. A multi-split can serve two or three bedrooms from one outdoor unit, and a zoned ducted system can cool the whole upper floor as a single zone. Individual units in every room is normally the most expensive way to solve it and the least tidy.

Will a home ventilation system cool my townhouse?

It can help you flush hot air out overnight, which is valuable. What it will not do is refrigerate the air — a ventilation system can only supply air at roughly the temperature of its source. On a 28-degree afternoon, that is not cooling. Ventilation and cooling solve different halves of the problem, and in a badly overheating townhouse you often want both.

Does running the heat pump in cooling mode cost a fortune?

Less than most people expect. Cooling a room by a few degrees is generally cheaper per hour than heating it by a lot in winter, because the temperature difference you are working against is smaller. Setting a sensible temperature rather than the lowest one available makes the biggest difference — and a system that has been serviced and has clean filters will always run cheaper than one that has not.

Getting your townhouse ready before the heat arrives

Forecasters expect El Niño conditions to peak over the 2026–27 summer, which for New Zealand usually means a drier season with more hot spells. If your townhouse struggled last February, it is likely to struggle again — and January is a bad time to join the queue for a cooling install.

Start with the free changes, because they genuinely work. If the bedrooms are still unbearable after that, get someone to look at the whole building rather than just quote you a box on a wall. Air Conditioning Group has been installing heat pumps, ducted systems and ventilation across Auckland for years, including a lot of new townhouses that were never designed with February in mind. Call 0800 224 123 or book a free assessment and we will tell you honestly what your place needs — including when the answer is a shade sail rather than a heat pump.