To permanently exterminate cockroaches in an existing house without using agents.

Invasion paths of cockroaches leading to the inside of the existing house are intercepted. The invasion paths are ventilation ports 1 for ventilating under floor formed in two or more spots between a foundation 2 and a substrate 6 by foundation packing method of construction. An eaves material 12 in which a folded part 15 having a U-shaped cross section is made by folding the material toward the inside is formed to protrude from the outer wall 5 on an overhang end 13 above the ventilation port 1. When a stepped part 16 is formed below the ventilation port 1, an elastic net material 3 having ≤3 mm maximum aperture is used and installed in a state in which the net material 3 is bent in a space between the folded part 15 and the stepped part 16 by bringing the width of the net material 3 to be larger than the distance D between the folded part 15 and the stepped part 16.

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