Damp in Wellington, and the houses it lives in
Above-average damp and mould
EHINZ found 22.6% of people in the Capital, Coast and Hutt Valley health district lived in a damp home in 2023, against 20.6% nationally. For mould bigger than an A4 sheet, the figures were 16.8% and 16.5%.
Humid winters
NIWA puts mean 9 am relative humidity at Wellington Airport at 77.6% across the year, peaking at 81.1% in June and July, just when the windows are coldest.
Older timber homes
Character precincts make many of the city's pre-1930s homes hard to demolish, and the Miramar state houses of 1937 were weatherboard with tiled roofs. Consumer NZ says positive pressure systems suit older houses with wooden joinery better than modern houses with sealed aluminium joinery.
Flats and apartments
The 2023 Census counted 30,390 Wellington City households in flats, townhouses and apartments. An apartment with a floor above has no roof space to draw air from, and outside vents may need the body corporate's agreement.
Sunny roofs, cold nights
The region's south-western tip gets more than 2,100 hours of bright sunshine a year, NIWA says. BRANZ warns that on overcast days and at night, roof space air may be colder than the rooms below, which matters for any system drawing from it.
Positive pressure or heat recovery in a Wellington house?
In a draughty villa or bungalow with timber windows, Consumer NZ's guidance points towards positive pressure. BRANZ adds that the more airtight a home, the more effective a positive pressure system is, so a very draughty house may need some draught-stopping too.
In a newer townhouse or a well-sealed renovation, balanced heat recovery is the stronger candidate. BRANZ says it makes most sense in a relatively airtight building, fitted during a new build or major renovation, and that it meets the Building Code's requirement for fresh outdoor air.
Be wary of anything that only moves roof space air around the house. In BRANZ's view, ducted warm air transfer systems don't meet Building Code clause G4, because they don't bring outdoor air inside.
And if a quote just says HRV or DVS, ask which type it is. Both are companies, not kinds of system.
Renting in Wellington
Landlords must meet the ventilation standard: openable windows in the living areas and bedrooms, and extractor fans venting outside in the kitchen and bathroom. Tenancy Services says recirculating systems, products like HRV and DVS systems, don't meet it.
What to ask a ventilation specialist
- Is my house airtight enough for this type to work well?
- Where does the air come from, and what happens when the roof space is colder than the house?
- Where will the fan unit go, and can a technician reach it safely later?
- Will any outside vent need the body corporate's agreement?
- Which registered electrician does the wiring, and when will the CoC arrive?
Your part, and the specialist's
You can
- Leave the bathroom fan running for a while after every shower.
- Wipe condensation off the windows each morning and note the worst rooms.
- Keep the living areas warm enough that moisture doesn't settle.
- In a flat or townhouse, check the body corporate rules.
Leave to a licensed installer
- Anything in the roof space.
- Fixed wiring for the fan and controller.
- Cutting ceiling outlets and outside vents, and weatherproofing them.
- Balancing supply and extract on a heat recovery system.
What we'd do
Our pick for a damp Wellington home
We'd start with heat and extraction: a heat pump keeping the living areas warm, and kitchen and bathroom fans that vent outside. If the windows still stream on winter mornings after a few weeks of that, we'd get a ventilation specialist to look at the joinery and the roof space. A timber villa often points to positive pressure and a tight modern flat to heat recovery, but we'd want their reasoning written on the quote.