John Tookey, Professor of Construction Management, Auckland University of Technology
New Zealand has just been hit by the first big cold snap of 2025 and, like every year, many New Zealanders will be reaching for an extra jumper, slippers and maybe a blanket to try and keep warm.
New Zealand’s housing stock has long been criticised for being damp, cold and ill-suited to the climate.
In the 2018 Census, households were asked about the state of their homes. According to Stats NZ, 318,891 homes in New Zealand (21.5%) were affected by dampness and 252,855 (16.9%) had visible mould larger than A4 size at least some of the time.
While the World Health Organization recommends a minimum indoor temperature of 18°C, many homes in New Zealand fall below these thresholds, with some experiencing temperatures less than 16°C.
Even when homes are built to code, there can still be issues and health risks. A lot of New Zealand’s housing is not fit for purpose – particularly at this time of the year.
While improving heating and standards is a homeowner choice, for landlords it is increasingly a requirement. Over recent years landlords have faced increasing costs to achieve legal heating, ventilation and insulation requirements within 90 days of a new or renewed tenancy.
For everyone else, there are ways to make homes more efficient to heat and comfortable to live in. Here are four ways to keep heat in your home this winter – some simple and affordable, while others are more of an investment.
Insulation is your friend
Firstly, insulation is our friend in winter. Double glazing is excellent but expensive (between NZ$450/m2 and $1500/m2) and subject to restrictions in heritage buildings. There are other options.
Secondary glazing with glass, acrylic or applique plastic sheets can be a significantly more cost-effective option.
Where possible, home owners should be looking at ways to add to thermal efficiency by increasing insulation.
Walls can be retrofitted with cavity fillers. If your budget can stretch to it, rigid insulation board is also effective. Under the floor and in the roof spaces are favourites for these upgrades. They are relatively cheap improvements to make and generally pay for themselves.
Target draughts
Secondly, a warm and dry home requires finding and eliminating draughts.
For many years, building scientists have sought to achieve airtight homes. An airtight home substantially reduces heat loss in winter.
Temporary and permanent improvements can be made by buying or making some draught excluders and door sweeps for doorways. But specialist products such as adhesive-backed foam tape or V-strip weatherstripping around door and window frames are also very effective.
Even just using masking tape during winter to seal the gaps in unused windows can help keep warmth in the home.
Windows and a compass
Third, use your window orientation strategically. Invest in heavier curtains (or blinds) that insulate windows. Then use a compass (you probably have a compass app on your phone) to work out which way is north.
North-facing windows catch the sun during the day, and contribute to thermal gain in a house. South-facing windows are in shadow all day and tend to act as a heat sink, losing energy throughout the day.
During the day, ensure curtains and blinds are open on the north side and closed on the south side. As soon as night falls, close the curtains to retain maximum heat. Try to keep unused rooms closed off and stick to the naturally warmer spaces.
Move heat around
Fourth, use ceiling fans, heat pumps, and dehumidifiers to maximise the available heat in your house.
Heat will stratify into layers in your house. It is always going to be warmer near the ceiling of each room. Usually, the loft space is the warmest of all through maximum thermal gain during the day.
Using a ducted heat pump can recycle that heat to the living spaces. Similarly, if you set the ceiling fan to move air around the room you will make the most of what you have. Ideally, run the ceiling fan backwards (clockwise) if it has that option, to create an updraught rather than a downdraught to aid circulation.
Dehumidifiers are extremely useful in increasing the feeling of warmth in a house. During operation, they release some latent heat while condensing water. Dry air is easier to heat, making your heating more efficient.
Your home can make you sick
Cold damp homes can have significant health impacts, including respiratory issues, rheumatic fever and skin infections – particularly for children and vulnerable people.
Targeting heat loss and dampness can help improve conditions. Will it ensure every home is warm and toasty? No. But these steps can make their homes just a little bit warmer – and healthier – this winter.
John Tookey does not work for, consult, own shares in or receive funding from any company or organisation that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.
