Pest ControlQuestion 220 of 319

Sealing exterior wall penetrations and pipe gaps as an exclusion measure: which gap size is small enough to keep out a MOUSE (the harder of the two to exclude)?

a.Any opening of 1/2 inch or smaller is fine — mice cannot fit through anything under 1/2 inch
b.Openings must be sealed to about 1/4 inch or smaller, because a mouse can squeeze through a gap of roughly 1/4 inch
c.A 1-inch gap is acceptable as long as it is round
d.Gap size does not matter; only rats need to be excluded

Explanation

Mice can squeeze through gaps roughly the size of a pencil — about 1/4 inch — while rats need only about 1/2 inch. So exclusion must close openings to about 1/4 inch or smaller to keep mice out. Use rodent-proof materials such as steel wool plus sealant, hardware cloth, or metal flashing — not foam alone, which rodents chew through.

Law Reference: FDA Food Code Ch. 6

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