Close-up of a large unsealed hole in a tan brick exterior wall where copper AC refrigerant lines wrapped in black foam insulation and silver duct tape enter the house, with open gaps around the pipes.
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Close-up of a large unsealed hole in a tan brick exterior wall where copper AC refrigerant lines wrapped in black foam insulation and silver duct tape enter the house, with open gaps around the pipes.

This photo shows a utility penetration where the AC refrigerant lines enter through the brick, and the hole was cut much larger than the pipes, leaving open gaps around foam insulation and duct tape. A mouse needs a gap no wider than a pencil and a rat one about the size of a quarter, so this opening gives rodents an easy way inside, and they chew through foam and tape with ease. Rodent proofing seals this kind of penetration with metal mesh and durable sealant to close it off for good.