Passive Design

Designing the building and the spaces within it to benefit from natural light, ventilation and even temperatures.

Controlling indoor air quality

Moisture and contaminants from building materials and activities such as cooking and heating can harm building occupants’ comfort and health.

Moisture generally results from activities such as cooking and washing, as well as from building occupants’ breathing, and from unflued gas heaters.

Common sources of contamination include smoking, building materials giving off volatile organic compounds (VOCs), and combustion (of gas, oil or wood) for cooking and heating, which gives off particulates, carbon, sulphur, nitrogen oxide and complex organic molecules such as polycyclic aromatic hydrocarbons.

Air may also be contaminated by biocontaminants such as mould and fungi spores.

Moisture can affect both thermal comfort and health. Common airborne contaminants have been linked to a range of symptoms such as headaches, sinus congestion, dizziness, nausea, irritations of the eyes, nose and throat, respiratory problems, allergies and neurological disorders.

Contaminants, including excess moisture, should be eliminated by removing the source of contamination – for example, by specifying low-VOC building materials – or installing extract fans as close as possible to the source. In June 2019, G4/AS1 was updated with a requirement for mechanical extract fans to remove moisture from rooms that contain cooktops, showers and baths in household units and accommodation units.

It is especially important to persuade householders not to use portable gas heaters because of the moisture they add to the air inside a house. In the 2018 Census, almost a third of the households that relied on portable gas appliances for home heating reported problems with mould.

BRANZ House Condition Surveys, conducted around every 5 years since 1994, have consistently found poor indoor air quality in New Zealand houses. The 2015/16 survey, for example, found that 11% of owner-occupied and 31% of rental houses felt damp. Assessors found signs of mould in almost half the houses visited.


Updated: 06 April 2020