Abstract: In the construction of a building, for example a house A, a plurality of composite assemblies, such as Pa . . . , are built of pairs of composite boards 2a and 3a . . . of prescribed thickness held apart by spacers 4a . . . of a prescribed width at a fixed spacing. The composite assemblies only are used to make up a wall W . . . and a ceiling C for separating upper and lower floors.Before the building of the house A begins, a flat foundation plane 24 is built of concrete over the ground E of the house A. A plurality of upright supports 21 . . . have anchor plates 21c . . . at the bottom thereof. The anchor plates 21c are secured to the foundation plane 24. The upright supports 21 . . . also include retainers 21j at the top thereof that are secured to a ground sill 23 as an outermost member of the house A. A cladding panel 22 is installed on the side of the retainer 21j to cover up the gap between the ground sill 23 and the foundation plane 24.