FRESH, CLEAN AIR | MENU
The Challenges:
The quality of the air inside our homes can have a very significant effect on our health, wellbeing and productivity:
“Every breath draws in not just oxygen but also invisible pollutants (dust, fungi, pathogens, chemicals, particulates and carcinogens)… People tolerate stuffy rooms or symptoms such as headaches, eye and nose symptoms, and asthma without recognising that these may be a sign of poor air quality… The evidence is clear that clean indoor air reduces illness, improves cognitive function, productivity and prevents the spread of respiratory infections.”
Julie Bennett and team, University of Otago, 2025:
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“The effects of pollutants can be acute and immediate (for example, allergies from dust mites) or chronic over a long term (for example, formaldeyde and spores from fungi).”
MBIE Building Performance, 2023:
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The NZ Building Code Clause G4 – Ventilation has the high-level objective to safeguard people from illness or loss of amenity due to lack of fresh air, including:
Adequate ventilation within buildings
An adequate number of air changes to maintain air purity
Construction and maintenance of mechanical ventilation systems to prevent harmful bacteria, pathogens and allergens from multiplying within them
Removal of cooking fumes and odours, moisture, fumes and gases, airborne particles, bacteria, viruses and other pathogens, and contaminated air
However the Building Code doesn’t require homes to have continuous fresh air ventilation – and many NZ homes rely on opening windows, ranch sliders and doors to provide fresh air.
Ventilation systems are further regulated under NZ Standard 4303 (1990) with provisions for both natural and mechanical ventilation, and requirements for fireplaces, clothes dryers, kitchen and bathroom exhaust fans, and air filters and dust collectors to protect against airborne contaminants:
“Microorganisms, dusts, fumes, smoke and other particulate matter may be captured by air filters. Many bacteria (99% exceed 1 micrometer in size) are attached to larger particles such as human skin flakes. Viruses generally occur in clusters or in and on other particles. Lung-damaging particles that may be retained in the lungs are 0.2 to 5 micrometers in size.”
Standards NZ:
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The lack of adequate ventilation also is a major factor in the build up of moisture inside the home leading to the growth of mould, which is a significant health hazard contributing to conditions such as asthma and respiratory disease. This is increasingly a problem with improved construction methods over more recent decades reducing the draughts and air leakage typical in earlier era housing:
“Homes built since the 1990s are much more airtight than older homes meaning that, while they are easier to heat, problems associated with inadequate ventilation have become more common. Because these homes have very low levels of background air leakage… condensation and damp will occur… Mechanical ventilation systems are best to maintain air quality… It is key that the supply air is taken from outdoors, not from the roof space, which can be polluted.”
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Options for Ventilation Systems:
Many Kiwi families are including ventilation systems in their new build or when renovating their existing home. Options include:
Mechanical ventilation systems, the most efficient with heat recovery
Establishing natural air flow or “stack effect” passive ventilation through the placement of windows
Superhome Certification requirements for VENTILATION are:
Base: Balanced whole home Mechanical Heat Recovery Ventilation system (MHRV) with exhaust and supply vents across the property. Fresh air supply, not to be sourced from the roof space.
Better: Base PLUS An efficiency of more than 75% with exhaust and supply vents across the property, including bathrooms. No standalone extraction fans.
Best: Better PLUS An efficiency of more than 80% installed inside the envelope with exhaust and supply vents across the property. including bathrooms. No standalone extraction fans. Designed and commissioned by a professional Superhome participant.
Homestar certification from the NZ Green Building Council also requires continuous mechanical extract ventilation:
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Passive House NZ notes that mechanical ventilation is not mandated by the Passive House standard but is “the easiest way to meet the energy goals and a precondition for reliable indoor air quality”:
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