PURPOSE: To facilitate an installation work of a foundation.

CONSTITUTION: A pair of dirt floor side edge frames 32 and 33 are installed so that they extend along both side edges of a dirt floor 12 which forms an entrance hall floor. The end of a sash receiving frame 35 is connected to each of these dirt floor side edge frames 32 and 33. The sash receiving frame 35 is placed in between the dirt floor side edges 32 and 33 so that a groove 16 which houses the sash receiving frame 35 may be properly placed in between foundations 14 and 15 on the sill side edges. This construction makes it possible to eliminate the need for a cut portion for the foundations on the dirt floor side edges, thereby simplifying the shape of an entrance hall foundation.