Rentals · Healthy Homes
Healthy Homes standards and windows: what landlords must do
The Healthy Homes standards do not require double glazing. Windows still matter for three of the five standards: heating, ventilation and draught stopping.
What would your windows save?
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What we found
Our calculations, data as of 23 October 2026
- No Healthy Homes standard requires double glazing. Landlords must stop unreasonable gaps that cause noticeable draughts, including around windows, and every habitable room needs openable windows or doors of at least 5% of its floor area.
- We ran the regulations’ heating formula for a typical 25 m² living room with 6 m² of windows. Double glazing lowers the required heating capacity by 11–12%: from 3.0 to 2.7 kW in Wellington and from 3.7 to 3.3 kW in Dunedin.
- That saving rarely changes which heater is needed. In none of the 15 cities did double glazing bring our example room to 2.4 kW or below, the threshold above which a fixed electric heater other than a heat pump generally cannot be used.
- Glazing does matter for the newer, gentler formula, which applies when insulation and glazing throughout the home meet NZS 4218:2009. Double glazing alone does not qualify an older house; the walls, ceiling and floor must meet that standard too.
Where windows appear in the standards
Draught stopping. Landlords must make sure the home has no unreasonable gaps or holes in walls, ceilings, windows, skylights, floors and doors that cause noticeable draughts. The age and condition of the house are no excuse. A loose sash or a cracked pane that whistles in the wind needs fixing; replacing sound single glazing does not.
Ventilation. Living rooms, dining rooms, kitchens and bedrooms need at least one window, door or skylight that opens to the outside and can be fixed open, with an openable area of at least 5% of the room’s floor area. Kitchens and bathrooms need extractor fans vented outside. If you add secondary glazing, the window behind it still has to be openable.
Heating. The main living room needs fixed heating that meets a required capacity, worked out with Tenancy Services’ heating assessment tool or the formula in Schedule 2 of the regulations. The window area and its R-value are inputs to that formula.
What double glazing does to the heating requirement
We applied the Schedule 2 formula for older homes to one example living room: 25 m² of floor with a 2.4 m stud, two external walls, 6 m² of windows, an insulated ceiling (2.9) and underfloor (1.3), and uninsulated walls (0.5). Each city uses the regulations’ assumed outdoor temperature. Single glazing is R0.15; double glazing is a low-E retrofit in aluminium frames at R0.30.
| City | Assumed outdoor °C | Single glazing, kW | Double glazed (R0.30), kW | Difference, kW |
|---|---|---|---|---|
| Queenstown | −6 | 4.0 | 3.5 | 0.48 |
| Taupō | −5 | 3.9 | 3.4 | 0.46 |
| Christchurch | −4 | 3.7 | 3.3 | 0.44 |
| Dunedin | −4 | 3.7 | 3.3 | 0.44 |
| Invercargill | −4 | 3.7 | 3.3 | 0.44 |
| Hamilton | −3 | 3.6 | 3.2 | 0.42 |
| Rotorua | −3 | 3.6 | 3.2 | 0.42 |
| Palmerston North | −3 | 3.6 | 3.2 | 0.42 |
| Nelson | −3 | 3.6 | 3.2 | 0.42 |
| Napier | −2 | 3.5 | 3.1 | 0.40 |
| Tauranga | 0 | 3.2 | 2.9 | 0.36 |
| New Plymouth | 0 | 3.2 | 2.9 | 0.36 |
| Auckland | 1 | 3.1 | 2.8 | 0.34 |
| Whangārei | 2 | 3.0 | 2.7 | 0.32 |
| Wellington | 2 | 3.0 | 2.7 | 0.32 |
The formula adds a fixed allowance of 40 W per m² of floor and a full air change every hour for older homes, so the windows are only part of the total. Halving their heat loss trims 0.3–0.5 kW, which might let you choose the next heat-pump size down but does not remove the need for a fixed heater. Your own room will differ; use the official tool.
The modern-dwelling formula
Since 2022, homes built to the 2008 Building Code, and rentals where insulation and glazing throughout meet or exceed NZS 4218:2009, can use a second formula with a lower air change rate and no per-m² allowance. It usually gives a smaller heater. Double glazing is one condition, not the only one; an older house with uninsulated walls does not qualify by changing its windows. The details are on Tenancy Services’ heating standard page.
What is worth doing in a rental
- Fix draughty sashes, broken panes and failed putty: required, and cheap.
- Make sure every habitable room has a window that opens and stays open.
- Treat condensation as a ventilation problem first: extractor fans, and a place to dry washing that is not the living room.
- Consider double glazing when replacing failed joinery, or for tenants’ comfort, but not as a compliance item.
Landlords are not eligible for Warmer Kiwi Homes grants; see grants and finance.
This week: Palmerston North
Single glazing in an aluminium frame runs below the dew point about 2,430 hours a year in Palmerston North (H1 zone 3); clear double glazing cuts that to 350. A low-E retrofit of 25 m² saves $190 a year heated mornings and evenings with a heat pump, or $569 heated all day. Fastest payback here: DIY magnetic secondary glazing, 17 years.
Cheap fix. EECA estimates that closing curtains before dark saves $80–90 a year. Lined, full-length curtains with a pelmet work best. Read more