About the indoor environment and health

This section gives background information about the indoor environment and how it affects our health.

In this section, indoor environment refers to three main aspects of housing:
- household crowding
- second-hand smoke exposure
- cold and damp houses. 

A poor indoor environment can affect our health

A poor indoor environment can affect our health. We spend much of our time indoors and at home, and so our indoor environment is very important for health.

The indoor environment can affect health through a range of ways: 

  • Household crowding increases the risk of infectious diseases, including  lower respiratory tract infections, meningococcal disease and gastroenteritis. 
  • Second-hand smoke can increase the risk of asthma,  lower respiratory tract infections, sudden unexpected death in infancy (SUDI), middle ear infections, and low birth weight in children, and ischaemic heart disease, stroke and lung cancer in adults.  
  • Cold and damp housing can worsen asthma symptoms, and is also associated with an increased risk of asthma development and respiratory tract infections. Cold housing may contribute to excess winter deaths.
  • Unflued gas heaters and open fires can cause respiratory problems and indoor dampness. Carbon monoxide from unflued gas heaters can cause poisoning.  

Other potential hazards from housing include old lead-based paint flakes, asbestos, pest infestations, and safety hazards.

Young children and the elderly are particularly at risk from the effects of poor housing.

Household crowding and health

Household crowding refers to houses that are too small for the number of occupants and need more bedrooms (‘structural crowding’). Also, functional crowding (room sharing) may occur when trying to save heating costs.

Household crowding can increase the spread of infectious diseases, particularly for children [1]. Families who live in crowded households are also a source of infectious disease in their wider community [2].  

In particular, household crowding can increase the risk of: lower respiratory tract infections (including pneumonia, bronchiolitis and bronchitis), meningococcal disease, gastroenteritis, Haemophilus influenzae (Hib) disease, Hepatitis A, Helicobacter pylori infection, and tuberculosis [1]. Studies also suggest that household crowding increases the risk of upper respiratory tract infections and trachoma (eye infection) [1]. 

A recent study estimated that 1,343 hospital admissions for infectious diseases were attributable to household crowding each year in New Zealand in 2007–2011 [1].

Read the latest statistics on household crowding on the household crowding webpage.

Read the latest statistics on lower respiratory tract infections and meningococcal disease.

Second-hand smoke and health

Second-hand smoke refers to the smoke breathed out by the smoker, and the smoke coming from the cigarette. When someone smokes in a confined area (such as in the home or car), it puts everyone’s health at risk. 

Young children are particularly at risk from the effects of second-hand smoke. In children, second-hand smoke increases the risk of asthma, lower respiratory tract infections, sudden unexpected death in infancy (SUDI), low birth-weight and middle ear infections (otitis media) [3]. In adults, second-hand smoke increases the risk of ischaemic heart disease, stroke and lung cancer [3].  

In 2010, an estimated 104 people died from second-hand smoke exposure in New Zealand [4,5].  

Read the latest statistics on second-hand smoke exposure in New Zealand on the second-hand smoke exposure webpage.

Read the latest statistics on asthma, lower respiratory tract infections, sudden unexpected death in infancy (SUDI), meningococcal disease, and the overall health burden due to second-hand smoke exposure in New Zealand.  

Cold and damp houses and health

Cold, damp and mouldy houses are a risk to health in several ways. 

Indoor temperatures below 16°C increase the risk of respiratory infections, and below 12°C stress the cardiovascular system [6]. Cold temperatures also contribute to excess winter deaths (increased number of deaths occurring in the winter months compared with other times of the year). The World Health Organization recommends a minimum indoor temperature of 18°C, or 20°C for houses with young children, elderly people or ill people.

Damp and mouldy housing can affect health in several ways, particularly respiratory health.  Dampness and mould growth can exacerbate asthma and increase the risk of asthma onset [6]. Indoor dampness and mould is also associated with an increased risk of respiratory tract infections and bronchitis [7]. Mould can irritate airways, and lead to respiratory toxin production and mould sensitisation [8,9].

Read the latest statistics about home heating on the home heating webpage.

Read the latest statistics on asthma and lower respiratory tract infections

Poor quality of housing in New Zealand

Many New Zealand houses are cold, and do not meet recommended minimum temperatures.  A 2006 study found low-income homes in New Zealand were colder than WHO guidelines: 16–17°C in living areas and 14°C in bedrooms on average [10].

Houses are cold mostly because they are difficult to heat. Two major reasons for this are (i) poor insulation and (ii) inefficient heating. 

Poor or lack of insulation is common in New Zealand homes, particularly in older houses.  Insulation reduces the rate of heat loss, helping keep homes warmer and drier. Poor or lack of insulation makes it hard to maintain indoor temperatures, leading to either high heating costs, or not using heating.  New Zealand houses built before 1 April 1978 were not required to have any insulation.

Most New Zealand houses had at least some insulation in 2010, which was an improvement from 2005 [11]. This may be due to recent government home insulation schemes and awareness campaigns (such as EECA’s insulation retrofit programmes and the Energywise information campaign). These campaigns have helped retrofit about 320,000 houses since 1996 (as at July 2014), particularly low-income houses. However, ceiling insulation often had defects like gaps. In 2010, almost half (45%) of houses did not have under-floor insulation (among those with accessible suspended floors) [11].

Damp homes can result from damp subfloors, unflued gas heaters, inadequate ventilation, having no extractor fan in kitchen and bathroom, and drying washing inside. Colder and/or poorly insulated homes are also likely to be damp, as water condenses more easily onto cold surfaces. Ventilation can also remove moisture from homes more effectively if the home is well heated. Damp houses can lead to mould growth.

Open fires are an inefficient type of heating system (producing little heat for the amount of fuel used), and contribute to indoor air pollution.

Unflued gas heaters produce carbon monoxide, carbon dioxide and nitrogen dioxide, which can be hazardous to health. Unflued gas heaters also produce a lot of moisture, which can exacerbate mould growth in homes.  

Any intervention that makes a house warmer, drier or safer has the potential to improve health. Making houses warmer through insulation and heating systems can improve both mental health and physical health (particularly cardiovascular and respiratory health) [6]. New Zealand studies have shown that insulating homes and improving heating reduced coughs and colds, and the number of sick days [10,12].

Children and older people more at risk

Young children and older people are particularly vulnerable to the effects of poor housing, as they spend proportionally more time indoors.

Children and infants are also more susceptible to indoor air pollutants. Children are still growing and developing, and have immature immune systems. They also inhale a larger dose of air per unit of body mass at a given level of activity than adults [13]. 

Read more about populations more at risk from environmental hazards on the 'who is more vulnerable' webpage.


1. Baker MG, McDonald A, Zhang J, Howden-Chapman P. 2013. Infectious Diseases Attributable to Household Crowding in New Zealand: A systematic review and burden of disease estimate. Wellington: He Kainga Oranga/ Housing and Health Research Programme, University of Otago. Available online: http://www.healthyhousing.org.nz/publications

2. McNicholas A, Lennon D, Crampton P, Howden-Chapman P. 2000. Overcrowding and infectious diseases - when will we learn the lessons of our past? New Zealand Medical Journal, 113(1121), 453-454.

3. US Department of Health and Human Services. 2014. The Health Consequences of Smoking – 50 Years of Progress. A Report of the Surgeon General. Atlanta, GA: US Department of Health and Human Services, Centers for Disease Control and Prevention, National Center for Chronic Disease Prevention and Health Promotion, Office on Smoking and Health.

4. Mason KM, Borman B. 2016. The burden of disease from second-hand smoke exposure in New Zealand. New Zealand Medical Journal, 129(1432): 16–25.

5.  Mason KM. 2016. The Burden of Disease from Second-hand Smoke in New Zealand. Wellington: Environmental Health Indicators Programme, Massey University. 

6. Braubach M, Jacobs DE, Ormandy D (Eds.). 2011. Environmental burden of disease associated with inadequate housing: A method guide to the quantification of health effects of selected housing risks in the WHO European Region. Copenhagen, Denmark: WHO Regional Office for Europe. Available online: http://www.euro.who.int/en/health-topics/environment-and-health/Housing-and-health/publications/2011/environmental-burden-of-disease-associated-with-inadequate-housing.-a-method-guide-to-the-quantification-of-health-effects-of-selected-housing-risks-in-the-who-european-region

7. Fisk W, Eliseeva E, Mendell M. 2010. Association of residential dampness and mold with respiratory tract infections and bronchitis: a meta-analysis. Environmental Health, 9(1): 72. doi: 10.1186/1476-069X-9-72

8. WHO. 2009WHO Guidelines for Indoor Air Quality: Dampness and Mould. Geneva: World Health Organization. 

9. Keall M, Crane J, Baker M, Wickens K, Howden-Chapman P, Cunningham M. 2012. A measure for quantifying the impact of housing quality on respiratory health: a cross-sectional study. Environmental Health, 11(1): 33. doi: 10.1186/1476-069X-11-33

10. Howden-Chapman P, Pierse N, Nicholls S, Gillespie-Bennett J, Viggers H, Cunningham M, et al. 2008. Effects of improved home heating on asthma in community dwelling children: randomised controlled trial. British Medical Journal, 337: a1411. doi: 10.1136/bmj.a1411

11. Buckett NR, Marston NJ, Saville-Smith K, Jowett JH, Jones MS. 2011. Preliminary BRANZ 2010 House Condition Survey Report - Second Edition. BRANZ Study Report 240.Judgeford: BRANZ Ltd.

12. Howden-Chapman P, Matheson A, Crane J, Viggers H, Cunningham M, Blakely T, et al. 2007. Effect of insulating existing houses on health inequality: cluster randomised study in the community. British Medical Journal 334(7591): 460. doi: 10.1136/bmj.39246.620486.AE

13. Miller MD, Marty MA, Arcus A, Brown J, Morry D, Sandy M. 2002. Differences between children and adults: implications for risk assessment at California EPA. International Journal of Toxicology 21(5): 403-418. doi: 10.1080/10915810290096630

Interested in more information?

Helene Marsters

Phone +64 4 979 3382 (ext 63382)
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