Air quality: The invisible element of a healthy home
In Aotearoa, we often define a 'healthy home' by what we can easily sense — temperature and humidity. We feel the cold when insulation is inadequate, and we see condensation forming on windows or the telltale black spots of mould. But there's a third element that's equally critical yet often overlooked because it's invisible: air quality.
The unseen health factor
While we can feel temperature and see moisture, air quality silently impacts our daily wellbeing. It determines how likely viruses are to spread within our whānau, whether dust mite allergies flare up, and how many harmful particles we unknowingly breathe in each day. For our most vulnerable — our tamariki, kaumātua, and those with existing health conditions — poor air quality can transform a home from sanctuary to health hazard.
At Toa Homes, we understand that true kaitiakitanga means addressing all aspects of home health, including those we cannot see.
Key air quality indicators
There are several critical measures of indoor air quality that directly impact our health.¹ Understanding these helps us appreciate why proper ventilation is so essential:
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CO₂ is a gas produced when we breathe and from combustion processes.
Health implications from high levels of CO₂:Drowsiness, headaches, and reduced cognitive function
Virus transmission risk increases as exhaled particles remain airborne longer²
Optimal levels:
Outdoor level: ~400 parts per million (ppm)
Good indoor quality: <800 ppm
Acceptable indoor quality: 800-1000 ppm³
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Particulate matter is the tiny particles suspended in air from bacteria, viruses, dust, smoke, pollen, mould and fungal spores, and other sources. PM2.5 and PM10 refer to different particle sizes.
Health implications from particulate matter:Can penetrate deep into lungs and bloodstream
Triggers asthma and allergies
Associated with respiratory and cardiovascular disease
Children's developing lungs are particularly vulnerable
Optimal levels:
PM2.5 <5 μg/m³ (annual)
PM10 <15 μg/m³ (annual)⁴
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VOCs are the chemicals released from building materials, furniture, cleaning products, and many household items.
Health implications include:
Short-term: Eye/respiratory irritation, headaches
Long-term: Liver/kidney damage, certain cancers
Can trigger asthma episodes
Some VOCs are known carcinogens
Optimal levels of total VOCs:
<500 μg/m³ (ideal)
<1000 μg/m³ (acceptable)⁵
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Humidity refers to the amount of moisture in the air.
Health implications of too low or too high levels of humidity:
Below 30%: Increases virus survival and transmission
Above 60%: Promotes mould growth and dust mite proliferation
Affects perception of temperature and comfort
Optimal levels:
40-60% is ideal range⁶
In the average New Zealand home without proper ventilation, CO₂ levels can easily exceed 1500 ppm during evenings when families gather, significantly increasing virus transmission risk.⁷ Studies show that reducing CO₂ to below 800 ppm can decrease airborne virus transmission by up to 60%,⁸ while effective filtration of particulate matter can reduce respiratory symptoms in children by nearly 30%.⁹
The air-tight solution
To tackle these invisible challenges, we approach air quality with precision and care:
First, we build an air-tight building envelope, essentially creating a controlled internal environment protected from the outside. We verify this seal using blower door tests that measure air leakage.
Then comes the crucial second step: controlled ventilation through mechanical ventilation with heat recovery (MVHR) systems.
Why we use MVHR
At Toa Homes, we've made a deliberate choice to install MVHR systems with F7 filters in every home we build, with the ability to upgrade to a HEPA filter.
We choose MVHR because it offers a comprehensive solution to air quality challenges. While opening windows might seem like a simple answer to ventilation, it introduces unfiltered air containing pollen, pollutants, and particles while allowing precious heat to escape. Traditional ventilation systems often address only part of the problem, either focusing on removing stale air or providing basic filtration without heat recovery.
MVHR systems represent the gold standard in ventilation technology, providing continuous fresh air without the energy penalties associated with traditional ventilation methods. By recovering heat from outgoing air, these systems maintain comfortable temperatures and ensure every room receives a steady supply of filtered, fresh air regardless of external weather conditions.
For families with allergy sufferers, young children, or elderly members, having consistently high air quality is particularly valuable. The MVHR system creates a protective boundary between the outside environment and your home's interior, giving you control over what you breathe.
While our MVHR systems provide continuous fresh air circulation, this doesn't mean you can't embrace natural ventilation as well. Doors and windows can absolutely be opened whenever you wish — we all cherish that seamless indoor/outdoor flow, especially during summer months. The beauty of an MVHR system is that it ensures clean, filtered air throughout your home all year round, particularly on days when opening windows isn't practical due to weather, allergies, or air pollution. It works silently in the background, giving you the freedom to ventilate naturally when conditions are favourable, while maintaining healthy air quality when they're not.
We include the cost of an appropriately specified MVHR system in the base level price of each of our set designs. We believe healthy air isn't a luxury upgrade, but a fundamental right that every family deserves, regardless of budget.
The national health impact
The consequences of poor housing reach far beyond individual homes. In New Zealand, housing-related illnesses cost our healthcare system hundreds of millions each year in preventable hospital admissions, medication, and lost productivity.
Research from Otago University estimates that respiratory conditions linked to poor housing cost the country approximately $218 million annually.¹⁰ When we factor in the long-term impacts on children's development and educational outcomes, the true cost becomes immeasurable.
At Toa Homes, our commitment to rangatiratanga means we refuse to build to minimum standards when we know better options exist. The building code represents a legal minimum, not a target for optimal health outcomes.
Through hihiritanga, we continuously seek better ways to build homes that serve as true places of sanctuary. A Toa Home with MVHR provides more than just shelter; it offers a controlled environment where air is continuously cleaned and renewed, creating a genuine haven for whānau to flourish.
A foundation for multi-generational health
When we prioritise air quality alongside temperature and humidity control, we're not just building comfortable homes — we're laying foundations for multi-generational health and wellbeing.
In a Toa Home, manaakitanga is built into the very air you breathe. The invisible becomes visible through improved health outcomes, reduced allergies, better sleep, and enhanced cognitive function. These benefits extend to everyone, but particularly to those most vulnerable among us.
By addressing all aspects of a healthy home — including air quality — we're forging a new housing pathway that supports the wellbeing, prosperity, and mana of all people in Aotearoa.
References
¹ World Health Organization. (2021). WHO global air quality guidelines: particulate matter (PM2.5 and PM10), ozone, nitrogen dioxide, sulfur dioxide and carbon monoxide. World Health Organization.
² Rudnick, S.N., & Milton, D.K. (2003). Risk of indoor airborne infection transmission estimated from carbon dioxide concentration. Indoor Air, 13(3), 237-245.
³ ASHRAE Standard 62.1-2022: Ventilation for Acceptable Indoor Air Quality.
⁴ World Health Organization. (2021). WHO global air quality guidelines: particulate matter (PM2.5 and PM10), ozone, nitrogen dioxide, sulfur dioxide and carbon monoxide. World Health Organization.
⁵ Health Canada. (2020). Residential indoor air quality guidelines: Volatile organic compounds. Government of Canada.
⁶ Arundel, A.V., Sterling, E.M., Biggin, J.H., & Sterling, T.D. (1986). Indirect health effects of relative humidity in indoor environments. Environmental Health Perspectives, 65, 351-361.
⁷ McNeil, S., Quaglia, L., Bassett, M., Overton, G., & Plagmann, M. (2022). Indoor air quality in New Zealand homes and schools. BRANZ Study Report SR463. BRANZ Ltd.
⁸ Peng, Z., & Jimenez, J.L. (2021). Exhaled CO₂ as a COVID-19 infection risk proxy for different indoor environments and activities. Environmental Science & Technology Letters, 8(5), 392-397.
⁹ Fisk, W.J., Eliseeva, E.A., & Mendell, M.J. (2010). Association of residential dampness and mold with respiratory tract infections and bronchitis: a meta-analysis. Environmental Health, 9(1), 72.
¹⁰ Howden-Chapman, P., Viggers, H., Chapman, R., O'Sullivan, K., Barnard, L.T., & Lloyd, B. (2012). Tackling cold housing and fuel poverty in New Zealand: A review of policies, research, and health impacts. Energy Policy, 49, 134-142.
