To allow the intake of air from outdoors, interrupt the discharge of air and to improve the indoor environment by fitting a seal member which is formed with seal lips at the tip, is nonpermeable, is bent indoors, and is elastically bendable to the lower end of an outer wall in contact with a foundation.

A unit fitted with a frame 3 for fixing a floor material 5 to an outer wall 2 via a connecting member 4 is mounted on a foundation 1, and the gap between the foundation 1 and the unit is sealed by a seal member 6 which is formed with seal lips 8a, 8b at the tip, is nonpermeable, is bent indoors, and is elastically bendable. The seal member 6 is fitted to the lower end inside of the outer wall 2 in contact with the foundation 1 with the seal lips 8a, 8b at its tip faced indoors. Wind pushes the seal member 6 indoors, air flows in from the space formed between the seal member 6 and the foundation 1. The seal lip 8a is pressed to the foundation 1, the discharge of air from the underfloor is hindered by the foundation 1 and interrupted, and the air is discharged from a room or a roof section. The outside air is temperature- conditioned under the floor, exerts moisture-proof and mildew-proof effects, and improves the indoor environment.