Rats have extremely strong teeth and powerful jaws that allow them to chew through a wide variety of materials found in walls and floors. This ability is one of the main reasons rats can easily get into homes and buildings, even if you think your house is "sealed up." They can chew through wood, plastic, soft metals, sheetrock (drywall), plaster, and even bricks or concrete if the material is old, cracked, or weak. However, there are some materials that are harder for them to get through, like solid steel and thick, smooth concrete.

Rats can chew through 1/2-inch drywall in under an hour when motivated. They can create a functional entry hole through a wooden sill plate in a single night. This speed is why discovering gnaw marks requires immediate action — the damage compounds rapidly.

Why Can Rats Chew Through So Much?

Rats' front teeth never stop growing. This means they need to constantly gnaw to wear their teeth down. Their teeth are stronger than aluminum and can bite with a pressure of up to 7,000 pounds per square inch. They use their teeth to test surfaces, make holes, and find food or safe hiding places. Their persistent chewing is how they survive in the wild and in urban environments.

Types of Walls and Floors Rats Commonly Chew Through

• Wood: Rats can easily chew through wooden walls and floors, including older floorboards and paneling. Even thick wood can be chewed through if rats are determined.
• Drywall and Plaster: The gypsum in drywall is very easy for rats to gnaw through, and thinner plaster walls are also at risk.
• Plastic and Insulation: Many household materials like plastic pipes, insulation, or vapor barriers are not a challenge for rats' teeth.
• Bricks and Concrete: While rats can't chew through solid, new concrete or dense, unbroken bricks, they can enlarge gaps, cracks, and weak spots in brick and concrete. If there is a hole or a deteriorated area, rats will chew and claw to make it bigger.

The most dangerous consequence of rats chewing in walls is electrical fire. Rats chew through wire insulation, exposing bare conductors that can arc and ignite wall insulation or framing. In the US, rodents are estimated to cause 20–25% of house fires of unknown origin. If you have rats in your walls, have an electrician inspect for wire damage.

Older NH homes are particularly vulnerable: knob-and-tube wiring (still present in some pre-1940 NH homes) has no ground wire and deteriorates faster when chewed. Cellulose insulation (common in NH retrofits) provides both easy burrowing material and excellent nesting material for rats. If your NH home has either of these features, rat wall damage is a more serious concern.

How Do Rats Get Into Homes Through Walls and Floors?

• Rats can squeeze through holes as small as a quarter (about 0.7 inches).
• They look for existing gaps around pipes, vents, cables, or where walls meet floors.
• If there is no hole, they may test the area by gnawing until they make an opening.
• Once inside partitions or flooring, they make tunnels and nests, further damaging the structure.

Which Materials Are Rat-Proof?

While rats can chew through most common building materials, there are some exceptions:

• Thick Sheet Metal: Steel mesh or thick galvanized steel that is at least 19 gauge or thicker is typically rat-proof.
• Concrete: Solid and unbroken poured concrete is usually too tough for rats. However, any small cracks can become entry points.
• Glass and Some Ceramics: Rats cannot chew through glass or glazed ceramic surfaces.

If you are attempting to block rat entry, use steel wool combined with caulk, or hardware cloth with openings smaller than 1/4 inch. Seal all gaps around pipes and utilities.

How to Stop Rats From Chewing Through Walls and Floors

• Regularly inspect your home, especially in basements, attics, behind appliances, and along exterior walls for chew marks or small holes.
• Seal up all holes bigger than a pencil with rat-proof materials like steel mesh, metal flashing, or concrete patch. Standard spray foam and caulk alone are not enough.
• Keep vegetation, trash, and clutter away from the sides of buildings as these give rats hiding places and places to start chewing.
• Address leaks or moisture problems, as these attract rats looking for water and soft, damp materials to gnaw through.
• Store food (including pet food and birdseed) in sealed metal or heavy plastic bins.

With these precautions and a clear understanding of how rats chew through walls and floors, you can better protect your home or business from infestation and property damage.

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