Street temperature and building characteristics as determinants of indoor heat exposure.

Higher temperatures are associated with morbidity and mortality. Most epidemiological studies use outdoor temperature data, however, people spend most of their time indoors. Indoor temperatures and determinants of indoor temperatures have rarely been studied on a large scale. We measured living room and bedroom temperature in 113 homes of elderly subjects, as well as outdoor temperatures, in two cities in the Netherlands. Linear regression was used to determine the influence of building characteristics on indoor living room and bedroom temperatures in the warm episode. During the warm episode, indoor temperatures were higher during the night and lower during the day than outdoor temperatures. Indoor temperatures on average exceeded outdoor temperatures. The weekly average indoor temperature in living rooms varied between 23.1 and 30.2 °C. Dwellings that warmed up easily, also cooled down more easily. Outdoor and indoor temperatures were moderately correlated (R = 0.36 and 0.34 for living rooms and bedrooms, respectively). Building year before 1930 and rooms being located on the top floor were associated with higher indoor temperatures. Green in the vicinity was associated with lower temperatures in bedrooms. This study shows that indoor temperatures vary widely between dwellings, and are determined by outdoor temperatures and building characteristics. As most people, especially the elderly, spend most of the time indoor, indoor temperature is a more exact predictor of heat exposure than outdoor temperature. The importance of mitigating high indoor temperatures will be more important in the future because of higher temperatures due to climate change.