Where Auckland's damp comes from
The air outside
NIWA puts mean 9 am relative humidity at 82% at Auckland Airport and 79% at Leigh, and says the surrounding sea keeps it high all year. That's why Auckland counts as humid next to other centres.
Mould, district by district
EHINZ says 21.8% of people in Counties Manukau, 20.3% in the Auckland health district and 17.9% in Waitematā lived with mould bigger than an A4 sheet in 2023. The national rate was 16.5%.
Heaters that add water
EHINZ says portable unflued gas heaters release water vapour, nitrogen dioxide and carbon monoxide indoors. They were a main heater in 3.7% of Counties Manukau homes in 2023, against 2.5% nationally.
Homes with no heat at all
The Auckland health district had the highest share of homes with no heating in the country in 2023, 6.6%, about three times the national 2.4%. Cold walls and windows are where moist air turns to water.
Old joinery and new builds
Villas were common in early 20th century Auckland and bungalows followed in the 1920s. Meanwhile apartments, units and townhouses grew to 27.9% of homes by 2023. The two kinds of house leak air very differently, and that shapes which system suits.
Which system suits which Auckland home?
Consumer NZ says positive pressure systems, which blow drier air in from the roof space or in some types from outside, suit older houses with wooden joinery better than modern homes with sealed aluminium joinery. That points many villas and bungalows their way. BRANZ adds a catch: the system only works if it supplies air faster than the house leaks it, so a ventilation specialist should look at how draughty yours is.
Balanced heat recovery draws in outside air and extracts stale air through a heat exchanger. BRANZ says it makes most sense in a relatively airtight building, fitted during a new build or major renovation, which describes a newer townhouse better than a villa. It's a bigger job: two sets of ducts, an intake and an exhaust.
BRANZ also warns that roof space air isn't fresh outdoor air, and that anything sold as heat recovery should actually contain a heat recovery device. Our ventilation comparison sets the types side by side, and the home ventilation page covers the install.
Heat and air, together
Ventilation doesn't warm a house. BRANZ says heat recovery systems cut heat loss but aren't heating systems, and Consumer NZ warns that blowing roof space air in during winter means turning your heating up. In a damp Auckland home, steady heating in the living areas and extractor fans that vent outside come first.
Renting the house out? The ventilation standard asks for openable windows and kitchen and bathroom extractor fans that vent outside. Recirculating systems don't count: Tenancy Services names products like HRV and DVS systems as unsuitable.
Before you choose a system
- Is this positive pressure or balanced heat recovery, and why that type for my house?
- Where does the incoming air come from, and what happens when the roof space is cold?
- Which rooms get outlets, and where do any extract points go?
- Which filters does it use, and how often will they need changing?
- Is a registered electrician wiring it in, and will a CoC follow?
What you can do now, and what's for the installer
You can
- Stop using an unflued gas heater indoors.
- Run the bathroom fan during and after showers, and the rangehood whenever you cook.
- Note which rooms show mould or condensation first, to tell the installer.
- Dry washing outside where you can.
Leave to a licensed installer
- All roof space work, including the fan unit and ducts.
- Fixed wiring for the system and the Certificate of Compliance.
- Cutting ceiling outlets and wall holes, and weatherproofing them.
- Setting and balancing the airflow.
What we'd do
What we'd do about an Auckland damp problem
We'd stop adding moisture first: no unflued gas heater, extractor fans that work, and a heat pump keeping the living areas warm through the evening. If the windows still run with water after a few weeks of that, we'd get a ventilation specialist to look at the joinery and the roof space before choosing a type. And we'd ask them to write down why that type suits this house.