PURPOSE: To prevent the leakage of water by a method in which an underground beam with continuous underground walls, a bottom slab and a water-weeping pipe is constructed, a water conveyance tube is laid, the underground outer wall side of the tube is covered with a water-impermeable sheet hung down from the upper end of the underground wall, and a floor slab and underground outer walls are constructed.

CONSTITUTION: Underground walls 1 are constructed on the peripheral side of a building 9 from the ground's surface, the inside of the walls 1 is excavated, and the concrete of a bottom slab 2 is placed. A water-weeping pipe 11 is fixed to the reinforcing bars of an underground beam 3, and the concrete of the beam 3 is placed. A water conveyance pipe 12 is set in contact with the walls 1 on the beam 3, a water-impermeable sheet 13 is hung down from the upper end of the walls 1, the outer wall side of the pipe 12 is covered with the lower end portion of the sheet 13, and concrete for the floor slab 4 and the underground outer walls 5 is placed. The sheet 13 used is one connecting from above to below, and the sheet 13 is laid by properly lapping its sideward portions.