Rodent-Proofing Your Home: How to Seal Out Mice and Rats

Traps remove the rodents you have. Sealing the house keeps the next ones from walking in. Rodent-proofing (pros call it exclusion) is the one step that makes a mouse or rat problem stay solved. This guide gives you a walk-around checklist, a list of materials that work and those that do not, and the habits that keep your yard from feeding rodents.

How small a gap rodents can use

Start with the numbers, because they decide what counts as a gap.

• House mice can get through an opening about 1/4 inch across, about the width of a pencil.
• Young rats can also use 1/4-inch gaps. Adult rats get through about 1/2 inch.

So the rule is simple: seal every opening 1/4 inch or larger. If a pencil fits, a mouse can get through.

Inspection walk-around checklist

Do this on a dry day with a flashlight, a pencil to test gaps, and a notepad. Mark every gap you find so you can come back with the right material.

Outside, at ground level

• Where the foundation meets the siding, and where the ground meets the foundation.
• Cracks in the foundation, slab or steps.
• Holes where pipes, electrical lines, cable, gas lines and the dryer vent enter the house.
• Air conditioner refrigerant lines and the hole they pass through.
• Crawl space vents and access doors.
• The bottom of every exterior door, including the garage door and the side door to the garage.
• Gaps in mobile home skirting.

Outside, up high

• Roof rafters, gables, eaves and soffits.
• Attic vents and roof vents.
• Gaps around windows, especially those without weather stripping.
• Tree limbs, vines and utility lines that give rats a path to the roof.

Inside

• Under, behind and inside kitchen cabinets.
• Around pipes under sinks and behind the washing machine, water heater and furnace.
• Around floor vents, dryer vents and floor drains.
• Behind the stove and refrigerator.
• Closet floors and corners, and where the floor meets the wall.
• Around the fireplace.
• The attic, basement and crawl space.

Materials that work and materials that fail

Rodents chew. Anything soft enough for their teeth is only a delay.

Back foam with metal. Foam is fine for sealing air leaks, but push steel wool or copper mesh into the gap first. The metal stops the teeth; the foam or caulk holds it in place.

How to seal the most common gaps

Pipes and utility lines. Pack steel wool or copper mesh around the pipe, then cover with caulk or mortar. For bigger holes, cut sheet metal or hardware cloth to fit around the pipe and fasten it down. The same goes for AC lines and cable entries.

Foundation cracks. Fill with mortar, concrete or a cement patch. For a hole larger than a few inches, put hardware cloth in first and patch over it.

Doors and door sweeps. Install a door sweep or weather stripping on every exterior door so the gap at the bottom is less than 1/4 inch. Rats can squeeze under a door with a 1/2-inch gap. If rodents have gnawed the bottom of a wooden door, cover the edge with sheet metal. Check the garage door too. Rubber and vinyl seals are easy for rodents to chew, so look for gnawed spots and gaps at the sides.

Vents. Cover crawl space, foundation and gable vents with galvanized hardware cloth fastened on all sides. Do not use chicken wire. Hardware cloth keeps the air moving while it keeps rodents out.

Windows and screens. Make sure windows close tightly and screens are intact.

The roof line. For roof rats, closing gaps at the eaves, vents and soffits matters as much as the foundation. Trim tree limbs so none come within 6 feet of the roof, and thin out vines on walls and fences.

Yard and storage habits

Sealing works best when your yard is not feeding and sheltering rodents right next to the house.

• Store grain, birdseed and pet food in thick plastic or metal containers with tight lids.
• Bring pet food in at night and feed pets only what they eat in one sitting.
• Keep compost bins well away from the house. Use rigid bins with lids.
• Move woodpiles away from the house and raise them at least a foot off the ground.
• Keep bird feeders away from the house and clean up spilled seed.
• Trim grass and shrubs near the house and clear brush and weeds.
• Pick up fallen fruit and nuts.
• Use trash cans with tight lids.
• Clear clutter in the garage and sheds, where rodents nest unseen.

When to rodent-proof: seasonal timing

Mice that live outdoors often move into homes in autumn when nights turn cold. The best time to seal is late summer or early fall, before that happens. Our seasonal pest calendar has reminders for the rest of the year.

If rodents are already inside, trap as well as seal. Trapping without sealing just makes room for new ones. Our guides to getting rid of mice and rats cover trapping, and traps vs. bait stations compares your options.

When to hire a pro for exclusion work

Plenty of rodent-proofing is DIY: a door sweep, a tube of caulk, a pad of steel wool and an afternoon. Hire a professional when:

• The gaps are on the roof line, eaves or gables and you are not comfortable on a ladder or roof.
• The foundation needs masonry repair or the crawl space is hard to get into.
• You have sealed what you found and rodents are still getting in.
• You have roof rats, which means sealing high and low on the whole house.

Ask for a written list of the entry points they found, the materials they will use for each, and whether the work comes with a warranty. Steer clear of any bid that relies on foam alone. Our guide to choosing a pest control company covers what else to ask.