One reason for the considerable public health interest in the home environment, particularly the indoor home environment, is because we spend so much of our lives in this setting. Risk assessment and management principles imply that even relatively low-risk exposures will become important if humans are exposed to them frequently and for prolonged periods and if such exposures are common across the population. Consequently, many countries have carried out time-microenvironment-activity studies to support improved environmental health policy development.1,2

New Zealand has not specifically measured the amount of time that we spend in the indoor home environment. However, it is possible to produce estimates by combining data from several sources.

This brief report provides estimates of the amount of time that New Zealander’s spend in the indoor home ‘microenvironment’ using the most complete available New Zealand data.

Method—We used two data sources that have measured the amount of time that New Zealander’s spend in various locations. These sources are the 1998–99 NZ Time Use Survey and the 1997–98 NZ Travel Survey.

Neither of these surveys recorded whether the participants were indoors or outdoors. However, specific studies have been carried out overseas that collected such information.

A telephone survey of time and activity patterns has been conducted in the United States. This was the National Human Activity Pattern Survey (NHAPS) based on 9386 participants interviewed over the 1992–94 period.5

A similar survey in Canada, the Canadian Human Activity Pattern Survey (CHAPS) was carried out from 1996–97 and included 2381 participants.6

Findings from these surveys are very similar.7 They show:

Results—Findings about place of activity from the NZTUS and NZTrS are shown in Table 1. A key observation is that we spend most of our lives at home (72–73%), followed by our work and study environment (12–13%), and transport environment (5–6%).

Combined with overseas estimates, these data suggest we spend about 70% of our lives in the indoor home environment, and a total of about 94% of out time indoors in buildings or vehicles.

Discussion—Findings from these surveys confirm that the home environment, particularly the indoor home environment, is the one where New Zealanders spend most of their lives. This result is consistent with the findings of time use surveys carried out in other developed countries. One difference is that New Zealanders appear to spend slightly more time at home that in other developed countries.

Estimates of time indoors at home are slightly lower for the US (65% of time indoors at home),7 Canada (66%),7 Germany (65%),8 and United Kingdom (67-68%).9 If the time spent at ‘other peoples houses’ was taken into account, then the time spend in New Zealand homes would be even greater than these estimates suggest.

The relatively large amount of time spent in the indoor home environment has notable public health implications. Hazards in the domestic environment become particularly important because of the long duration of exposure. For example, domestic exposures in New Zealand homes to dust mites,10 endotoxins,11 and mould12 are associated with asthma.

Moreover, the home is an important setting for transmission of some infectious diseases, such as meningococcal disease, where the risk for children is greatly increased by household crowding.13 Because the indoor home environment is unregulated, it remains an important setting for passive smoke exposure.14 15

Cold damp housing is associated with poor health outcomes, and conversely, improving such conditions with home insulation results in significant health improvements.16

The most vulnerable groups of the population also spend more of their time in the home environment. These groups include infants and children, the elderly, and those with disabilities and chronic illnesses such as COPD.17 Such vulnerability, coupled with long periods of exposure to the domestic environment, is reflected in the high rates of home injuries seen in children.18

The time-use findings presented here have several limitations. Probably the most important is our reliance on overseas estimates of the split of indoor and outdoor time. The estimates used here were based on large surveys conducted in the United States and Canada. Despite different methods, the findings for these countries were very similar.7 It seems reasonable to conclude that the indoor-outdoor mix is not markedly different in New Zealand, though that assumption needs to be investigated further.

Statistics New Zealand has developed a proposal for a repeat time-use survey to be carried out in 2008/09. They have consulted widely regarding the content and method for this survey and are considering several important extensions, including broadening it to all age groups, and recording of indoor-outdoor location.

Results from this survey will be useful in providing more precise estimates of the relative importance of environmental exposures for New Zealanders. Ultimately, New Zealand may also need to consider a range of other more specialised approaches to provide time-microenvironment-activity data for specific purposes.19