How New Zealand homes are getting smarter

As the cost-of-living climbs and climate consciousness deepens, a new wave of New Zealand homeowners are turning to ‘certified Passivhaus’ homes. Sometimes mistakenly referred to as ‘passive homes’, they’re referring to buildings that have been certified to the International Passivhaus Standard. This building standard ensures that the properties are ultra-efficient buildings designed to stay naturally warm in winter and cool in summer, all while using a fraction of the energy of conventional houses. Once seen as a niche European import, Passivhaus design is fast becoming a blueprint for the future of sustainable living across Aotearoa.

WHAT ARE THE KEY DESIGN PRINCIPLES OF A CERTIFIED PASSIVHAUS?

Passivhaus certified homes and buildings are designed to work with nature, not against it, using clever architecture, design and engineering to create a stable, comfortable environment year-round. Built around principles of site-specific insulation, airtight & thermal bridge free construction, considered windows, and heat recovery ventilation, they minimise heat loss and maximise energy efficiency.

Joe Lyth from the Passive House Institute New Zealand says careful design and selection of the windows will help capture warmth in winter, while shading prevents summer overheating.

“But you also need to make sure there isn’t too much glazing to the east and west.”

Orientation plays a key role too, with north-facing living spaces harnessing natural sunlight for passive heating. Thermal modelling allows the design to be tailored to the context, ensuring the design is appropriate for the site, and the local climate.

“A certified Passivhaus also comes without leaks and drafts. As a metric to achieve that you need to have only 0.6 air changes an hour, whereas in new builds there are usually between three to five.”

Lyth says that doesn’t mean you can’t open your windows, it’s just about preventing moisture and air from getting into your walls and ceiling.

“It’s the goldilocks standard of housing where it’s never too hot or too cold, with the temperature always sitting between 18 and 24 degrees all year round.”

As part of the design, you also require a balanced mechanical ventilation system.

“That means you're bringing in the same amount of air as you're taking out at the same time. You're not having to open windows, and it's also not putting any pressure on your building envelope. We leave our windows open most of the summer, but we know the ventilation system will keep all of the building ventilated, all the time, whether we open them or not”

HOW DO YOU GET CERTIFIED?

Lyth says achieving Passivhaus Certification is similar to getting building consent. “Just like you comply with the building code, you also comply with the Passivhaus standard. It’s not a rating system or a tick box exercise.”

“You have to achieve the requirements around energy use, overheating, moisture control, air tightness and ventilation as well as making sure the building is low energy and comfortable. The Passivhaus process is incorporated into the design, and not something at the end of the process. It goes to a third-party assessor to check all the requirements of the standard have been achieved.”

You can turn an existing house into a Passivhaus Certified home or you can choose to build one from scratch, with the standard stating that you can’t use any more than 15 kilowatt-hours, per metre squared per year to heat the building to 20 degrees also taking into account any on-site power generation from solar or similar. “Most new builds in New Zealand use around 100 - 120 kilowatt-hours per m2 per year for heating demand.”

But if you don’t quite meet the levels required Lyth says there’s something called the low energy standard which can still be achieved.

“That’s around 30 kilowatt-hours per m2 per year, which is still a significant step up from the energy efficiency of most new builds.”

DO REQUIREMENTS DIFFER BY REGION?

As every region delivers varying temperatures and conditions, the requirements for a certified Passivhaus can also vary based on your geographical location, which is why a model is used to determine what needs to be done.

“We use something called the Passive House Planning Package. It's an Excel spreadsheet-based energy model containing weather data from every climate station in New Zealand over the past 30 years.”

“Every certified Passivhaus that’s modelled, is modelled for that specific site based on actual climate data and context, so it works anywhere.”

Lyth says you then input the site, the orientation of the building and any site shading.

“You also put in the type of windows and glass you're using, the type of ventilation system, and the hot water systems, and it gives you an instruction book on what you need to do.”

“The same building in the middle of a forest is going to perform differently to if it was in the middle of a field. The model allows you to tailor the design and specification, to ensure the required level of performance is achieved.”

WHAT DOES IT FEEL LIKE AND WHAT ARE THE BENEFITS?

Lyth says he lives in a certified Passivhaus and that everything about it feels “just right.”

“It's still, it's quiet, and because of the air tightness that also means less sound leakage from the outside. The whole building internally is about the same temperature, so you don't get cold in one room and have to heat another one.”

He also says the benefits are huge.

“A big reason I built one is for health. I did this because my kids were getting really sick in minimum code, mouldy houses, but within about four days of moving into our current home, they didn't need their inhalers anymore and haven’t since.”

“Because the air is filtered there’s far less allergies too, as pollen and insects aren’t coming into your home because you’re opening the windows for ventilation.”

Lyth says a huge benefit is also the savings on your power bill.

“When we first built our house our energy bills were about $120 a month all year round. When we then invested in a small five kilowatt solar system, those bills dropped to about $50 a month.”

“We’ve saved a lot. Previously we were paying the same amount for a granny flat that we used to rent which was a third of the size of the home we live in now, but was always uncomfortable to live in.”

IS IT EXPENSIVE TO BUILD A CERTIFIED PASSIVHAUS?

Lyth says it can be more complex to turn an existing property into a certified Passivhaus home, but building from scratch is a different story.

“We started out by saying we want to achieve Passivhaus performance, weighed every design decision, and that cost us $2600 per square metre to build four years ago, which was actually less than a building code house for a one off architectural build at the time.”

“In my own practice I have four projects on site at the moment seeking Passivhaus certification, and all of them are being built for around the same square metre cost as most one-off building code houses.”

Lyth says he’s also working on one in Blenheim that’s costing just over $5000 per square metre, and down the road a ‘standard’ home is being built for the same cost.

“So it doesn't have to cost more, if you think about it from the start.”

“It may mean some compromises on high-end design and finishes if you’ve set yourself a strict budget but those things date over time, and can always be changed. There’s also no point in having a $50,000 kitchen if it’s going to be freezing all the time.”

Lyth says changing people’s perceptions is key.

“There needs to be an understanding that it doesn't have to cost more, but that's because you're moving some of the budget from this area to this area.”

He also believes one of the biggest barriers is a lack of education about the Passivhaus standard.

“We’re conditioned to think that growing up in a colder home is normal, so a warmer home can feel too warm – when in reality it’s just keeping us healthy”.

“There’s a lot of misconceptions around Passivhaus performance being over the top because we’re so used to a much lower standard of living.”

ARE THERE ANY FINANCIAL INCENTIVES?

With existing special lending rates for sustainable building initiatives, does the same apply to a home aiming for Passivhaus certification?

“Right now banks aren't naming Passivhaus certification as something that will guarantee a discount, but when we spoke to them about our house, they agreed to let us have it.”

Lyth says while it may not be advertised, it’s still worth raising it with your bank knowing that the benefits of Passivhaus certification are high – lower bills, less sickness, a more durable building with less maintenance, and the confidence of an internationally recognised certification.

“We’ve been discussing with the banks around including Passivhaus certification in their green home offerings, there is movement in the industry with councils recognising Passivhaus certification on LIMs, and the potential for Passivhaus certification as a pathway towards a faster consenting process.”

So in a world increasingly defined by rising energy costs and environmental awareness, certified Passivhaus buildings stand out as one of the smartest solutions for the future of housing in New Zealand. They prove that comfort and sustainability can coexist beautifully, offering warm, quiet, healthy spaces that demand minimal energy to run.