In order to obtain fundamental data on the thermal performance of a semi-underground house, a twin-type test house was constructed on a university campus in September 1984. The test house has two rooms with south-facing windows above the ground surface and a corridor between the two rooms. The floor level is 1.3 m below the ground surface. Insulation of 0.1 m depth and 1.35 m width was installed horizontally around the room on the east at a level of 0.3 m below the ground surface. This insulation is called "horizontal insulation". The room on the west has no such insulation. The total heat transmission rate of the construction above the ground surface per unit floor area is about 1.2 W/K.m2. Both rooms were very airtight, compared to other recently constructed detached houses in Japan. Long-term field measurements were made in two situations - one in which the rooms had weather shutters (from soon after construction until October 8, 1985) and the other in which there were no shutters (from November 1, 1985, to March 31, 1987). There was no auxiliary heating or cooling system during the experiment. Our study clarified that horizontal insulation was effective in reducing the annual temperature fluctuation of indoor air.

KEYWORDS: thermal insulation, earth sheltered housing, measuring, testing, heat flow, horizontal, rooms, transmittance, shutters, experiment, air tightness, indoor air, temperature, Japan.