Burning up: Why it's too hot in the city for Kiwi homes

OPINION: In New Zealand, when we discuss how well our homes perform, more often than not the talk is about how our homes are too cold.

However, AUT studies have shown how extensive overheating is in this country: some of our homes are chronically overheated up to 75 per cent of the time in the summer.

And, surprisingly, the problem was worse where the homes had more insulation. We are "building tight" without "ventilating right".

Overheating is particularly critical in apartments, where the combination of expanses of glazing and the shared inter tenancy walls and floors limit the ability of the apartment to lose heat. In a single detached dwelling this heat is lost through the greater external surface area of the building – the outside walls and roof - which individual apartments don’t have.

Overheating creates an unhealthy living environment. There is a significant amount of scientific literature on the effects of overheating on comfort and health and thermal discomfort is, as the name suggests, not pleasant. Worse, over prolonged periods, it may actually lead to severe health impacts.

Heat-related illnesses and mortality can occur when the human body's ability to thermo-regulate is impaired. That’s what the body does to maintain a core temperature of between 36.1°C and 37.8°C, by balancing heat generation and loss. Luckily, bodies can cope with temporary increases of up to 38°C or 39°C without causing damage to health, influenced by factors such as temperature, humidity, air movement, radiant energy exchange, the built environment and behaviour.

Medical evidence suggests that in the short term health effects can be mild (within limits). Longer-term exposure to high temperatures can cause more severe problems and fatalities, particularly for vulnerable groups, and increase the risk of other causes of mortality. Cardiovascular and respiratory diseases account for the majority of heat-related deaths. 

Unfortunately, there is a lack of research at present on defining night-time thermal comfort, but we do know that sleep loss contributes to health risks and a loss of productivity.

What we also know is that we all respond to heat in different ways, which makes it challenging to define acceptable thresholds for physiological response functions.

International summer indoor comfort temperature thresholds for non-air-conditioned dwellings show people start to feel increasingly uncomfortable when living area operative temperatures rise above 25°C and when bedroom temperatures rise above 23°C.

Temperature thresholds are OK in principle, but it should be about comfort, which does vary in people. I personally am comfortable at a lot lower temperatures than 23°C, and am more comfortable sleeping in temperatures about 18°C.

What is comfortable for you? Everybody has a thermal comfort level. Men have a higher metabolic rate to women, so our thermal comfort levels differ.

So, what an you do if you live in an apartment that gets too warm?

Stop the solar heat gain 

Obviously, it may be difficult to have your windows open all of time if you're concerned about security, or keeping out noise, weather and pollutants.

The solutions are to either retrofit a window film or hang a gauze-like material outside to window to limit the solar heat gain by preventing much of the heat from getting to the glazing but still allows some light in.

Purge ventilate

If you have an extractor fan (if you're renting that is now a legal requirement), use it. Set it on a timer for say 4 am so that it brings in as much of the cooler night-time air as possible.  

Air conditioning 

This is not available to all of us, it costs a lot to run and the carbon footprint is not good (some refrigerants used in air conditioning units require 1000g of CO2 for every gram of refrigerant produced).

However, if you are living in unhealthy conditions above 40 °C at least, you can get some respite. If you are renting, by law, your landlord will shortly need to provide a heat pump, so request that this heat pump also has a cooling function.

We'd like to see buildings in Aotearoa designed with the occupants in mind.

Like Goldilocks said when she was stealing the bears' porridge: ‘It is too hot or too cold but for too short a time is it just right.’

- James Powers is director of Oculus Architectural Engineering