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The work in this thesis examines the land utilisation and simulated thermal performance of a pair of two-storey, three bedroom, semi-detached earth sheltered houses based on an existing residential development in South Wales, UK. When designed as Exposed South Wall type earth sheltered houses, which incorporate a number of passive solar design principles, each house provides a ratio of 0.508 for the internal floor area to the overall plot area, which is more efficient than 0.319 for a non earth sheltered house on the same development site. The simulation study has shown that the temperature of the earth sheltering the ground floor rooms is relatively stable on the coldest and warmest day of the CIBSE test year of 1985, but fluctuates widely on the same days at 1500 mm below ground level. The stable earth temperatures enable the ground floor rooms in twenty computer models to record higher resultant temperatures than the first floor rooms, on both the above days. In addition, the temperature range between models in the ground floor rooms is much smaller than in the first floor rooms where there are three variations of earth cover of 1500, 750 and 250 mm. With 100 mm of externally placed polystyrene insulation and an exposed, insulated and south facing first floor wall, 1500 mm of earth sheltering and family occupancy is required, so that both the ground and first floor rooms record resultant temperatures between 18 and 21 °C. With an insulated first floor buffer wall and Trombe wall or a non-insulated first floor buffer wall and insulated passive solar conservatory higher resultant temperatures are recorded and thinner earth covers become feasible with family occupancy. By increasing the insulation to 300 mm of polystyrene the thickness of earth cover and the inclusion of a first floor passive solar collector becomes less significant in recording comfortable internal resultant temperatures. However, the internal resultant temperatures exceed the upper comfort temperature of 23 °C in most rooms in the family and single adult occupied earth sheltered houses. Three optimum design solutions are given which record comfortable internal temperatures and that provide designers with a choice of earth cover, first floor design configuration and insulation thickness.