Ambient and indoor temperature affects thermal comfort and human health. In a changing
climate with a predicted change in temperature extremes, understanding indoor temperatures, both
hot and cold, of different housing types is important. This study aimed to assess the hourly, daily
and monthly variation in indoor temperatures in different housing types, namely formal houses,
informal houses, flats, government-built low-cost houses and old, apartheid era low-cost housing,
in five impoverished urban communities in Johannesburg, South Africa. During the cross-sectional
survey of the Health, Environment and Development study data loggers were installed in 100 homes
(20 per suburb) from February to May 2014. Indoor temperature and relative humidity were
recorded on an hourly basis. Ambient outdoor temperatures were obtained from the nearest
weather station. Indoor and outdoor temperature and relative humidity levels were compared;
and an inter-comparison between the different housing types were also made. Apparent temperature
was calculated to assess indoor thermal comfort. Data from 59 retrieved loggers showed a significant
difference in monthly mean indoor temperature between the five different housing types (p < 0.0001).
Low cost government-built houses and informal settlement houses had the greatest variation in
temperature and experienced temperatures between 4 and 5 C warmer than outdoor temperatures.
Housing types occupied by poor communities experienced indoor temperature fluctuations often
greater than that observed for ambient temperatures. Families living in government-built low-cost
and informally-constructed homes are the most at risk for indoor temperature extremes. These types
of housing should be prioritised for interventions aimed at assisting families to cope with extreme
temperatures, gaining optimal thermal comfort and preventing temperature-related health effects.