L3 Public Health The Built Environment and Health

Overview

The lecture covers the built environment as a determinant of health and health equity, working from the global scale inwards. It opens with the burden of disease attributable to housing (indoor and ambient air pollution, slums, homelessness), then sets out two competing ways of modelling how housing produces health outcomes: a linear social-determinants-to-outcomes chain, and a complex system of interacting feedback loops. It then quantifies the Aotearoa New Zealand burden (cold, damp, mould, crowding), covers climate change as both a housing hazard and a feedback, and presents the interventions that address these: retrofitted energy efficiency, the Healthy Homes Standards, and state housing provision. The second half widens from the dwelling to the neighbourhood and city, arguing that car-dependent urban form is a public health problem comparable to tobacco, and closes with what clinicians can do at individual and population level.

Learning objectives

1. Understand the role of housing in health equity globally and in Aotearoa.
2. Be able to describe two interventions to prevent illness in NZ housing.
3. Understand city design as an important influence on health and health equity.
4. Be enabled to start taking action for healthy equitable housing and urban planning.

Framing: SDG 11 (Sustainable Cities and Communities) is positioned as a driver of SDG 3 (Good Health and Well-Being).

Global burden of disease due to housing

Leading risk factors for disease burden, 2021, ranked by DALYs per 100,000 population (all ages), colour-coded by category (metabolic, behavioural, environmental/occupational):

Rank	Risk factor	Category	Approx. DALYs/100,000
1	High systolic blood pressure	Metabolic	~2.8k
2	Smoking	Behavioural	~2.1k
3	High fasting plasma glucose	Metabolic	~2.0k
4	Low birth weight	Behavioural	~1.9k
5	High body-mass index	Metabolic	~1.6k
6	Ambient particulate matter pollution	Environmental/occupational	~1.5k
7	Short gestation	Behavioural	~1.4k
8	Household air pollution from solid fuels	Environmental/occupational	~1.4k
9	High LDL cholesterol	Metabolic	~1.1k
10	Kidney dysfunction	Metabolic	~1.1k

Key point: the two environmental risks in the global top ten, ambient particulate matter and household air pollution from solid fuels, are both products of the built environment and how homes are heated and cooked in.

Warning

Exact DALY values are not printed on the chart and were estimated visually from bar length. Learn the ranking and the categories rather than the numbers.

Illustrations of the two ends of the global housing problem: traditional open-fire cooking (Guatemala), showing indoor air pollution from solid fuels; and the Red Road high-rise flats (Glasgow), showing high-density urban housing.

Slums

• Before COVID-19, the share of the urban population living in slums had risen to 24% in 2018.
• 1.1 billion urban residents were living in slums in 2020.
• A further 2 billion are expected in the next 30 years.

Homelessness

Definition (NZ Stats): “a living situation where people with no other options to acquire safe and secure housing are without shelter, in temporary accommodation, sharing accommodation with a household, or living in uninhabitable housing.”

Four categories making up this definition:

• Street homelessness / rough sleepers
• Housing with inadequate conditions
• Temporary / emergency accommodation
• “Hidden” homelessness

Homelessness is a breach of human rights that leads to further breaches: work, healthcare, social security, privacy, education.

Scale: an estimated 1.6 billion people in inadequate housing globally, 150 million homeless, and more than 41,000 in New Zealand.

Air pollution and health in Aotearoa (HAPINZ 3.0)

Key findings of the Health and Air Pollution in New Zealand 3.0 study:

• Air pollution does significant harm to our people, especially our tamariki.
• Clean air matters to Kiwis: improvements in air quality make a difference to people’s health.
• Human-made air pollution caused 1.745 million restricted activity days (2016).

Cases per year attributable to each pollutant (2016):

Health outcome	Fine particles (PM2.5)	Exhaust gas (NO2)
Premature deaths (adults)	1,300	2,000
Cardiovascular hospitalisations (all ages)	2,600	2,000
Respiratory hospitalisations (all ages)	2,000	6,500
Asthma prevalence (0 to 18 years)	not shown	13,200

Social cost of these health impacts: $15.6billiontotal,split$6.16 billion for PM2.5 and $9.45 billion for NO2.

Sources of that cost:

• PM2.5 cost: 74% domestic fires, 17% motor vehicles, 8% wind-blown dust.
• NO2 cost: 100% motor vehicles.

Note that percentages may not add to 100 due to rounding. The source split is the point to remember: home heating dominates particulate harm, while traffic accounts for the whole of the NO2 harm.

How housing affects health: two models

Linear cause and effect

Howden-Chapman et al. 2022 present a five-tier chain running upwards:

1. Social determinants: sociodemographic factors (age, sex, ethnicity, disability, family type) and economic factors (wealth, income, power, education, other resources).
2. What people can afford: type and quality of housing, and the operating costs associated with housing (heating, water, maintenance).
3. Housing features: durability and quality of structure; outdoor pollutants (e.g. radon, carbon emissions); immediate housing environment including accessibility; insulation and weatherisation including ventilation; connection to infrastructure; heating and cooling facilities; building materials (e.g. lead, asbestos, PCB, and indoor pollutants such as mould and fuel); water and sanitation; adequacy of space; tenure security.
4. Health hazards: injury hazards, lack of social participation, neighbourhood noise, lack of physical activity, high or low temperature, poor indoor air quality, harmful substances, contaminated water, crowding, unstable housing.
5. Poor health outcomes: injury, poor quality of life, hearing impairment, cardiovascular disease, respiratory disease, impaired brain development, cancer, infectious and vector-borne disease, poor mental health.

A return arrow runs from poor health outcomes back to social determinants, labelled “health affects capacity to earn and save”, so even this linear model contains a poverty-illness feedback loop.

A complex system

Macmillan et al. 2016 mapped the links between housing policy and environmental, economic, social and health outcomes as a complex system. Variables interact and change over time through feedback loops and reinforcing cycles rather than linear cause and effect. The interacting nodes mapped were:

• Ventilation and indoor air pollution
• Household crowding
• Housing affordability
• Fuel poverty and indoor temperature
• Energy efficiency and climate change
• Community connection and quality of neighbourhoods
• Land ownership, value and development patterns

Warning

Individual arrow directions and pairings between the nodes were not fully distinguishable at render resolution. The examinable point is the overall structure, that these variables are mutually interlinked with no single linear causal path, not the specific arrows.

Housing and health in Aotearoa: the burden

Annually in New Zealand:

• More than 600 hospitalisations due to damp or mould
• 1,500 hospitalisations attributable to injuries
• 625 hospitalisations due to cold housing
• 500 hospitalisations due to household crowding
• 230 deaths attributable to these conditions, more than half due to damp or mouldy homes

Cold, damp and mould

• 2018 Census: one third of people live in damp and/or mouldy homes.
• 2020 General Social Survey: one third of homes have a daytime temperature below 18 degrees.
• Consequences: respiratory symptoms, acute respiratory admissions, asthma in children.
• Ventilation balance is often a problem (the trade-off between ventilating for moisture and losing heat).

Ingham 2019 (Thorax) measured housing features in homes of children admitted with acute respiratory infection (188 cases) versus controls (454 controls), giving crude odds ratios relative to no evidence of the feature:

Mould feature	Cases	Controls	Crude OR (95% CI)
Any mould on walls/ceiling	147 (78%)	310 (68%)	1.67 (1.12 to 2.48)
Any mould on joists	23 (12%)	25 (6%)	2.39 (1.32 to 4.33)
Musty smell	30 (16%)	46 (10%)	1.68 (1.03 to 2.76)

All three odds ratios exceed 1 with confidence intervals excluding 1, so each mould feature is significantly more common in the homes of children admitted with acute respiratory infection.

Household crowding

• Definition: a household is crowded if it needs one or more additional bedrooms; crowding is severe if it needs two or more.
• Crowding is linked to infectious disease, with an estimated 500 hospitalisations per year attributable to household crowding in NZ.

Percentage of people living in crowded households:

Census year	Total	Māori (total response)	Pacific (total response)
2006	10.4%	22.8%	42.6%
2013	10.1%	20.0%	39.8%
2018	10.8%	20.8%	38.5%

Important

National crowding has been essentially static since 2006, but Māori experience roughly double and Pacific peoples roughly four times the national rate, despite some decline in both groups since 2006. Crowding is one of the clearest examples of housing as a driver of health inequity.

Housing and climate change

Climate-related threats to housing:

• Flooding
• Wildfires
• Sea level rise
• Coastal erosion
• Displacement
• Heating and cooling homes

Illustrated by flooding of a Whakatāne residential neighbourhood (2017) and the Los Angeles fires (2025).

Reinforcing feedback loop (labelled R): use of fossil-fuel-powered air conditioning increases greenhouse gas emissions, which drives climate change, which raises average indoor temperature, which increases the use of fossil-fuel-powered air conditioning. Cooling homes with fossil fuels therefore makes the problem it is solving worse.

Interventions in NZ housing

Retrofitting energy efficiency

Evidence from He Kāinga Oranga on insulating and heating existing homes:

• Improved self-reported health and well-being
• Reduced GP visits, and reduced hospitalisations for respiratory and cardiovascular disease
• Reduced pharmaceutical usage and fewer days off school
• Reduced mortality in those over 65
• For every dollar spent, $4 returns to government in healthcare savings

Healthy Homes Standards

• Aim to address cold, damp, drainage and draughts in rental properties.
• Full implementation by July 2025.
• Regulations set minimum standards for heating, insulation, ventilation, moisture ingress (dampness) and drainage, and draught stopping.

State provision and regulation

• State housing has existed in NZ since the early 1900s, now around 70,000 houses.
• Government intervened in the housing market to ensure workers had housing and to reduce slums.
• It deals with private rental issues of high rents and poor quality housing.
• It helps address generational inequities and lifts people out of poverty.
• Government benefits from lower illness costs: the Social Housing Outcomes Worth study found a one third reduction in hospitalisations when families were re-housed into state houses.
• Policy is not fixed in one direction: government funding and the stock of social housing were subsequently reduced, and the current government has made eligibility criteria stricter and evictions easier.

Neighbourhoods, suburbs and cities

• Cities are now the dominant human habitat, with implications for social, physical, mental, economic and environmental wellbeing.
• Retrofitting is possible for neighbourhoods as well as houses, for example traffic calming and green space.
• Contrasting designs: Stonefields, Auckland, a dense conventional car-oriented subdivision, versus Earthsong cohousing, Ranui, Auckland, clustered housing with shared garden paths and solar panels.

Are cars the new tobacco?

Health impacts of car dependence (Douglas et al. 2011):

• Physical inactivity
• Obesity and related disease
• Death and injury from crashes
• Cardio-respiratory disease from air pollution
• Climate change

The tobacco analogy extends to the politics:

• The car lobby resists measures that would reduce car use, using tactics similar to those of the tobacco industry.
• Sprawling neighbourhoods reinforce car dependence.
• Car ownership and use have greatly increased in recent decades, with little public support for measures that would reduce this.
• 8 out of 10 new cars bought in NZ are gas-guzzling utes or SUVs.
• Advertising for these vehicles is pervasive, to the point that even MetService carries it.

Transport systems and health

Randal et al. 2022 modelled health gains from transport change, in health adjusted life years (HALY) per person, split by exposure pathway (physical activity, air pollution, road injury) and population group:

Group	Approx. total HALY/person
All	~0.29
Māori females	~0.37
Non-Māori females	~0.22 (lowest)
Māori males	~0.54 (highest)
Non-Māori males	~0.31

Physical activity contributes the largest component for Māori females, while road injury dominates for Māori males. Māori of both sexes show larger transport-related health gains than non-Māori, so transport intervention is also an equity intervention.

Warning

Precise per-segment HALY values are not printed on the chart and were estimated visually from bar height. Learn the pattern (who gains most, and via which pathway) rather than the figures.

Street design

US suburbia is frequently developed without sidewalks, with houses set back behind lawns and cars parked on the roadside, in contrast to a vibrant pedestrian mall such as Pearl Street, Boulder, Colorado, with people walking, trees, seating and shopfronts.

Investments in slowing traffic and in making it easier and safer to walk and cycle return tens of dollars saved for every dollar spent, a cost-benefit ratio better than most primary or secondary healthcare interventions.

The role of clinicians

Taking a built environment history:

• Housing questions
• Neighbourhood questions

Individual level treatments:

• Referral to housing insulation programmes
• GREEN prescription
• Advice about heating

Population level treatments:

• Te Whatu Ora partnership in housing and transport
• Te Whatu Ora influence on housing, land use and transport policy
• Civic engagement: voting, and influencing policy and politics
• Work for NGO efforts, for example Cosy Homes Trust

Important

The slide emphasises the population level treatments. Clinical action on the built environment is not limited to referring individual patients; it includes using the health sector’s institutional voice in housing, land use and transport policy.

Self-test

1. List the four learning objectives of this lecture.
2. Which two environmental risk factors appear in the 2021 global top ten leading risk factors for disease burden, and where do they rank?
3. Define homelessness as used by NZ Stats, and list the four categories that make up it.
4. State the global and New Zealand figures given for inadequate housing and homelessness.
5. Describe the trend in slum populations reported before COVID-19 and the projection for the next 30 years.
6. According to HAPINZ 3.0, what were the total annual social cost of human-made air pollution and its split between PM2.5 and NO2?
7. Distinguish the source profile of PM2.5-attributable costs from that of NO2-attributable costs in HAPINZ 3.0.
8. Describe the five tiers of the linear housing-to-health model in order, from social determinants to outcomes.
9. Explain how the linear housing model incorporates a feedback loop despite being drawn as a chain.
10. List the variables mapped in the complex-systems model of housing and health, and explain what modelling housing as a complex system adds beyond the linear model.
11. List the annual New Zealand hospitalisation and death figures attributable to poor housing conditions.
12. State the 2018 Census and 2020 General Social Survey findings on damp, mould and indoor temperature, and the health outcomes linked to them.
13. Interpret the Ingham 2019 odds ratios: which mould feature carried the highest odds ratio, and what does the confidence interval tell you?
14. Define household crowding and severe crowding, and describe how crowding rates differ by ethnicity in the 2018 Census.
15. Describe the reinforcing feedback loop linking air conditioning and climate change.
16. List the health, service-use and economic benefits of retrofitting energy efficiency reported by He Kāinga Oranga.
17. List the five areas covered by the minimum standards in the Healthy Homes Standards, and state the full implementation date.
18. Explain the public health rationale for state housing provision, including the quantified evidence given.
19. Explain the argument that cars are “the new tobacco”, covering both health impacts and industry behaviour.
20. In the Randal 2022 transport modelling, which population group had the largest total health gain and which exposure pathway dominated for that group?
21. Compare the cost-effectiveness of investment in slowing traffic and in walking and cycling infrastructure with that of clinical healthcare interventions.
22. A 3-year-old is admitted for the second time this winter with an acute respiratory infection. The family rents a home with visible mould on the ceiling, a musty smell, and a daytime living-room temperature of 15 degrees, and shares three bedrooms between seven people. Using the lecture content, identify the housing hazards present and the interventions and referrals available to you as a clinician.
23. Integrative: using both the housing and the transport material, explain why interventions in the built environment are described as health equity interventions in Aotearoa.

Answers

Reveal answers

1. Understand the role of housing in health equity globally and in Aotearoa; be able to describe two interventions to prevent illness in NZ housing; understand city design as an important influence on health and health equity; be enabled to start taking action for healthy equitable housing and urban planning.
2. Ambient particulate matter pollution, ranked 6th (~1.5k DALYs/100,000), and household air pollution from solid fuels, ranked 8th (~1.4k DALYs/100,000). Both are classed as environmental/occupational risks.
3. “A living situation where people with no other options to acquire safe and secure housing are without shelter, in temporary accommodation, sharing accommodation with a household, or living in uninhabitable housing.” The four categories are street homelessness / rough sleepers, housing with inadequate conditions, temporary or emergency accommodation, and “hidden” homelessness. It is a breach of human rights that leads to further breaches of rights to work, healthcare, social security, privacy and education.
4. An estimated 1.6 billion people in inadequate housing globally, 150 million homeless, and more than 41,000 in New Zealand.
5. The share of the urban population living in slums rose to 24% in 2018 before COVID-19, with 1.1 billion urban residents living in slums in 2020 and a further 2 billion expected in the next 30 years.
6. $15.6billionintotalfor2016,madeupof$6.16 billion attributable to fine particles (PM2.5) and $9.45 billion attributable to exhaust gas (NO2). Human-made air pollution also caused 1.745 million restricted activity days.
7. PM2.5 cost was 74% domestic fires, 17% motor vehicles and 8% wind-blown dust, so home heating dominates. NO2 cost was 100% motor vehicles.
8. (1) Social determinants: sociodemographic factors (age, sex, ethnicity, disability, family type) and economic factors (wealth, income, power, education, resources). (2) What people can afford: type and quality of housing and its operating costs (heating, water, maintenance). (3) Housing features: structural durability and quality, outdoor pollutants, immediate housing environment and accessibility, insulation and ventilation, infrastructure connection, heating and cooling, building materials and indoor pollutants, water and sanitation, adequacy of space, tenure security. (4) Health hazards: injury hazards, lack of social participation, noise, lack of physical activity, temperature extremes, poor indoor air quality, harmful substances, contaminated water, crowding, unstable housing. (5) Poor health outcomes: injury, poor quality of life, hearing impairment, cardiovascular and respiratory disease, impaired brain development, cancer, infectious and vector-borne disease, poor mental health.
9. An arrow labelled “health affects capacity to earn and save” runs from poor health outcomes back to the social determinants tier, so ill health reduces income and resources, which in turn worsens what housing people can afford.
10. Variables: ventilation and indoor air pollution; household crowding; housing affordability; fuel poverty and indoor temperature; energy efficiency and climate change; community connection and quality of neighbourhoods; land ownership, value and development patterns. Modelling it as a complex system shows that these variables interact and change over time through feedback loops and reinforcing cycles rather than a single linear causal chain, so an intervention in one place has effects elsewhere in the system.
11. More than 600 hospitalisations due to damp or mould, 1,500 attributable to injuries, 625 due to cold housing, 500 due to household crowding, and 230 deaths attributable to these conditions, more than half of them due to damp or mouldy homes.
12. 2018 Census: one third of people live in damp and/or mouldy homes. 2020 General Social Survey: one third of homes have a daytime temperature below 18 degrees. Linked outcomes are respiratory symptoms, acute respiratory admissions and asthma in children; ventilation balance is often a problem.
13. Any mould on joists carried the highest crude odds ratio at 2.39 (95% CI 1.32 to 4.33). Because the confidence interval does not include 1, the association is statistically significant. The same applies to any mould on walls or ceiling (1.67, 1.12 to 2.48) and musty smell (1.68, 1.03 to 2.76).
14. A household is crowded if it needs one or more additional bedrooms, and severely crowded if it needs two or more. In 2018 the total rate was 10.8%, compared with 20.8% for Māori and 38.5% for Pacific peoples (total response), so roughly double and roughly four times the national rate respectively.
15. Use of fossil-fuel-powered air conditioning increases greenhouse gas emissions, which drives climate change, which raises average indoor temperature, which increases the use of fossil-fuel-powered air conditioning again. It is a reinforcing loop in which the cooling response worsens the underlying cause.
16. Improved self-reported health and well-being; reduced GP visits; reduced hospitalisations for respiratory and cardiovascular disease; reduced pharmaceutical usage; fewer days off school; reduced mortality in over-65s; and $4 returned to government in healthcare savings for every dollar spent.
17. Heating, insulation, ventilation, moisture ingress (dampness) and drainage, and draught stopping, in rental properties, with full implementation by July 2025.
18. State housing was introduced to ensure workers had housing and to reduce slums, and it addresses private rental problems of high rents and poor quality, generational inequity and poverty. Government also benefits financially through lower illness costs: the Social Housing Outcomes Worth study found a one third reduction in hospitalisations when families were re-housed into state houses. NZ now has around 70,000 state houses, though funding and stock were later reduced and the current government has tightened criteria and made evictions easier.
19. Health impacts of car dependence are physical inactivity, obesity and related disease, death and injury from crashes, cardio-respiratory disease from air pollution, and climate change. On the industry side, the car lobby resists measures that would reduce car use using tactics similar to the tobacco industry, sprawling neighbourhoods reinforce dependence, car use has risen with little public support for reducing it, 8 out of 10 new cars bought in NZ are utes or SUVs, and advertising is pervasive, even on MetService.
20. Māori males had the largest total health gain at approximately 0.54 HALY per person, with road injury the dominant exposure pathway for that group. Māori females were next (~0.37), with physical activity the largest component; non-Māori females were lowest (~0.22).
21. Investment in slowing traffic and in making walking and cycling easier and safer returns tens of dollars saved for every dollar spent, a cost-benefit ratio better than most primary or secondary healthcare interventions.
22. Hazards present: damp and mould (mould on ceiling plus musty smell, both associated with acute respiratory infection admissions in Ingham 2019), cold housing (below the 18 degree threshold), and household crowding (needing additional bedrooms, linked to infectious disease and around 500 NZ hospitalisations per year). Clinician response: take a built environment history covering housing and neighbourhood; individual level treatments include referral to a housing insulation programme, advice about heating, and a GREEN prescription; the rental should meet the Healthy Homes Standards for heating, insulation, ventilation, moisture and drainage, and draught stopping; at population level, support re-housing pathways such as state housing (one third reduction in hospitalisations in the Social Housing Outcomes Worth study) and Te Whatu Ora partnership and policy influence in housing.
23. Both housing and transport hazards fall unevenly. Māori and Pacific peoples experience roughly double and roughly four times the national household crowding rate, and the housing model shows that social determinants such as income and power determine what housing quality people can afford, which sets their exposure to cold, damp, mould and crowding, with ill health then feeding back to reduce earning capacity. In transport, the modelled health gains from change are largest for Māori males and Māori females, so acting on the built environment removes exposures concentrated in the groups with the worst outcomes, rather than distributing benefit evenly. Both are also upstream and highly cost-effective ($4 back per dollar for retrofits, tens of dollars per dollar for walking, cycling and traffic calming), which is why they are framed as equity interventions rather than individual clinical care.