Are we building homes suitable for extreme heat?

Sunday, 4 February 2024

The record high temperatures seen this summer are set to become more normal as this century goes on.

Sweltering temperatures this summer are a forerunner of times to come, but a vast amount of New Zealand’s housing stock is not suitable for extreme heat.

There have been record high temperatures in many regions, and that has left many people enjoying days at the beach and pools, and ice cream sales booming.

But coping with very hot weather is difficult for the elderly, the unwell, and infants, and heat can be a killer.

In the United States, average annual heat-related deaths rose by 95% between 2010 and 2022, according to the Center for Disease Control and Prevention. Extreme heat across Europe in the summer of 2022 caused more than 60,000 deaths, a study in Nature Medicine found.

While New Zealand has not experienced heatwaves of the same level, Te Whatu Ora - Health New Zealand says there is already an average of 14 high-heat-related deaths each year.

And the risk of heat-related deaths is increasing globally as temperatures rise.

Niwa climate, atmosphere and hazards manager Nava Fedaeff says last year was New Zealand’s second warmest year on record, just shy of the record set in 2022.

The last three years were the country’s three warmest on record, but as the world continues to warm those recent records will be short lived, she says.

It is likely that many of New Zealand's homes are unsuitable for much higher temperatures, Waikato University’s Luke Harrington says.

“Because of the different ingredients in the mix that drive our weather we will still occasionally experience cooler periods, but climate change tips the scales towards warmer weather and makes more hot days likely in the future.”

University of Waikato climate change lecturer Luke Harrington says if global temperatures rise another two degrees, the most extreme temperatures seen in summer in Christchurch will become 10 times more frequent. For Auckland, that number is nearer 50.

“That won’t translate to an equivalent increase in heat-related hospitalisations and deaths, but the numbers will rise, and potentially rapidly, if we don’t adjust how we build our homes or modify our behaviour.”

It is very likely that many of New Zealand's homes are not currently suitable for much higher temperatures, he says.

“A lot of the issues which make our housing stock too cold and damp in the wintertime also translate to issues with keeping indoor temperatures cool in the peak of the summer.

“We should be adopting as many of the guidelines as possible that exist elsewhere. The issue of extreme summertime heat in New Zealand is only going to get worse. That’s a fact.”

Many European countries, and parts of the US, have maximum heat standards for bedrooms, or for inside, and requirements for shading on buildings in their regulations.

There is no minimum requirement around overheating in the Building Code.

Green Building Council chief executive Andrew Eagles says there is nothing similar in the Building Code here, and no minimum requirement to analyse or model for overheating.

But in the Homestar system, which rates the health, efficiency, and sustainability of homes, a calculation is compulsory, and it must be demonstrated heat will not exceed 25C for more than a set period, he says.

In a six star rated home heat must not exceed 25C for over 7% of the time, while in seven to eight star rated homes, the time reduces to 5%, then 3%.

Given the impact of rising temperatures, and ‘urban heat islands’ caused by concrete and glass build up in cities, having heat standards is a good way to address the issue, he says.

“We think more people should be doing it, and that it should be included in MBIE’s building for climate change programme. But we have heard nothing from the new government about that.”

There are a number of solutions builders can use to ensure homes are more resilient to heat, Eagles says.

These include reducing the glazing size of windows, setting windows further back in the structure, enabling cross ventilation with window and door placements, and putting on external shutters for shading.

Planting more trees to provide shade and soak up heat also helps, while homes with lighter coloured roofs have been found to be 4C cooler on an average day than dark roofed homes.

In New Zealand, the focus has been on poor-quality, cold, damp homes, AUT professor John Tookey says.

It depends on the design of the house, but some new very airtight, insulated new builds have greater potential to overheat than older homes with more gaps, although those gaps create other issues, he says.

“Architects are increasingly aware of these issues, and are incorporating more passive house building principles into their designs. Building to the Homestar rating systems also helps.

“But New Zealand is not at an advanced stage in addressing overheating when building new homes, or retrofitting existing ones. It happens a lot overseas, but we need more awareness and education here.”

One reason heat has not factored on the local building industry’s radar much is the country’s problem with cold, damp and mouldy homes.

AUT construction professor John Tookey says while there are no specific standards around overheating in the Building Code, “we can’t use that as a cudgel to beat the government with”.

Successive governments have focused on issues around poor-quality, cold, damp homes because of the associated health problems, he says.

“It is necessary to look at the housing stock in its entirety, and whether its summer or winter, ask if it is fit for purpose.

“Fundamentally, we are trying to improve the stock, but it is something that will be challenging to make good over a short timeframe.”

Heat pumps have an air conditioning cycle as well as a heating function.

It is also about the priorities of homeowners, and they tend to invest in addressing problems that are imminently pertinent to them, he says.

“In a country like Saudi Arabia where it is searingly hot, they would be more worried about heat. But here, issues with cold and damp come first, because they cause real problems now.”

But it is worth bearing in mind that the solutions for problems with cold, damp, mouldy homes also help to address heat issues, Tookey says.

“Insulation keeps homes warm when it's cold, but also keep homes cooler when its hot. It’s the same with heat pumps as they have an air conditioning cycle as well as a heating function.

“Humidity makes temperatures feel unbearably hot, but it also heightens the cold and makes things damper. A quick fix for humidity is a dehumidifier which helps all those problems.”

But much greater use of air conditioning and heat pumps would also increase the use of power from the energy grid, which is a problem in itself, he says.

“That is where using passive home principles in building can help, especially when they are assisted by careful building management systems, and have scope for future adaptation.

Changes to clause H1 of the Building Code will help to keep temperatures more consistent in new builds.

“Technology allows us to design in a more adaptive manner, and to work out where to position shades, ducts, and vents, how to use them in the most effective manner, and how to optimise thermal gain.”

There are things you can do when building new, or with existing buildings, to mitigate higher temperatures, but people need to be aware of them, he says.

New Zealand Certified Builders chief executive Malcolm Fleming says there is increasing use of passive, more climate conscious building techniques in the residential sector.

But it is in pockets, and mainly at the high end, rather than in more run of the mill homes, he says.

“The idea of passive, lower carbon, energy efficient homes is very appealing, and architects are more aware of the principles, while builders are keen to understand them.

“Unfortunately, for many people there is an inhibitor to translating thoughts into activity, and that is the cost. They like the idea until the costs come up, and then they don’t like the idea.”

There are changes designed to better address climate concerns afoot in the sector, he says. His organisation is refreshing its certified plans, and the brief includes sustainability and affordability.

And significant changes to clause H1 of the Building Code, which regulates the energy efficiency of buildings, came into effect late last year.

“The H1 changes meet some requirements around changing climate conditions, and will assist in keeping temperatures more consistent in homes going forward.

“But there does need to be a bit of stick from regulators around this, or good intentions will turn to nothing because people will say they can’t afford to do what is required.”