PURPOSE: To shorten the term of work by holding at least the upper end of a sheet between a ceiling beam and the upper end of a stud and closing an opening section formed among the ceiling beam, a floor beam and the stud by the sheet.

CONSTITUTION: A wooden stud 3 is installed between a wooden ceiling beam 1 and a wooden floor beam 2. The upper end section of a windbreak sheet 4 backed to a polyethylene sheet by a nonwoven fabric is held between the ceiling beam 1 and the upper end of the stud 3. The lower end section of the windbreak sheet 4 is held between the floor beam 2 and the lower end of the stud 3, and an opening section formed among the ceiling beam 1, the floor beam 2 and the stud 3 is closed by a sheet 4. An external wall panel 5 is mounted on the surface side of the windbreak sheet 4.