Transition in housing design and thermal comfort in rural Tanzania

This study evaluates the performance of three low-income passive housing designs at providing thermal comfort for their inhabitants in temperate tropical rural Tanzania. Severe climatic conditions in these upland regions include large daily oscillations in air temperature (14°C-36°C) and high levels of solar radiation, causing overheating which affects inhabitant health and wellbeing. Inadequate shelter in these difficult climatic conditions is a widespread problem with 71% of Tanzanians living in rural areas, of which 28% of are below the national poverty line. Over the last 10 years an increasing number of houses are using modern building materials (brick or concrete walls and iron roof) rather than traditional vernacular design (mud-pole walls and thatch roof). Three designs were chosen to describe this transition. The performances of the three houses were simulated across a study year using IES and then compared against five chosen criteria to assess thermal comfort. Detailed analyses of critical times of day and specific areas of the building envelope were used to identify critical areas of design. The traditional house overheated significantly less often with smaller diurnal indoor temperature swings than the modern houses (due to its higher roof insulation and wall thermal mass). It also experienced uncomfortably low temperatures least often but maintained higher temperatures for longer during hot evenings. The modern houses outperformed the traditional house in ventilation gains with constant heat rejection throughout the day and night. The traditional house’s open structure resulted in high daytime ventilation gains and night-time heat rejection. Consideration of the position and internal gains of each room was found to be an important design factor. Across the study year the traditional design provided greater thermal comfort. However, as durability and social pressures are important factors in the choice of building materials, the design of modern materials that can mimic and improve on traditional material performance is critical to improving the health of inhabitants.