How to Pest-Proof Your Home (the exclusion checklist that works for most pests)

The short answer

Pests need four things to move in: food, water, a place to hide, and a way to get inside. UC IPM names these as the four major contributors to infestations. The EPA puts the same idea more directly: “Remove sources of food, water and shelter.” Close the entry points with a material a mouse, rat, or cockroach cannot gnaw through. Cut off food and water. Remove the harbourage that lets them move from outside to inside without being seen. That sequence handles most household pests - mice, rats, ants, cockroaches, spiders, silverfish, and wasps setting up under the eaves.

Walk the outside first

Most people seal from the inside. The hole you can see on the inside wall is rarely the hole the pest actually used. Walk the outside in daylight with a flashlight and work from the ground up.

• Foundation and sill plate. Settled foundations open seams where wood framing meets concrete. Rats burrow along these.
• Utility penetrations. Every hose bib, gas line, dryer vent, AC line set, and cable box has trim around it. The gap beside the trim is the entry. The EPA’s pest-control do-and-don’t list says to “use steel wool to fill spaces around pipes,” right alongside the rest of the sealing advice.
• Weep holes. The small vertical slots in brick veneer above the foundation exist so the wall cavity can drain. Do not seal them solid. Stuff them with copper mesh so they still breathe.
• Vents. Foundation, crawlspace, attic, dryer, and gable vents all need covers. Cornell IPM is explicit on materials: galvanized sheet metal screwed down for raccoons, galvanized hardware cloth (quarter-inch or half-inch mesh) for mice and bats, with quarter-inch recommended “for smaller vertebrates, such as mice and bats.” Half-inch is stronger but less flexible. Replace plastic gable louvers with metal.
• Garage door corners and the gap under the door. A worn corner seal leaves a triangular gap. Replace the bottom seal and the corner weatherstripping as a pair.
• Roofline. Soffit-to-fascia seams, plumbing vent stacks, and where wires enter the attic. Cornell IPM specifically calls out “roof vents” whose best models are “totally enclosed to prevent birds and rodents from nesting inside,” plus ridge-line vents whose end caps “frequently work loose.”
• Chimney. A code-compliant metal chimney cap, not a homemade screen. Cornell notes that “many homemade chimney covers do not meet legal safety requirements.”
• Vegetation. Trim tree branches back from the roof and siding. Remove dense ivy and shrubs touching the wall. Move firewood, leaf piles, and deep mulch back from the foundation.

What actually seals a gap

The material rule is the same whether you are dealing with mice, rats, cockroaches, or wasps. Pests either gnaw, pry, or squeeze through the gap. Match the patch to the chewing risk of the animal.

• Steel wool packed into the opening, then sealed over with caulk. The EPA lists both together: caulk cracks and crevices, and use steel wool around pipes. The caulk alone fails on a gap a mouse chews; the steel wool alone falls out. Together they hold.
• Galvanized hardware cloth over vents and larger openings. Quarter-inch for mice and bats; half-inch where you need strength. Staple the cloth over the vent frame and seal the edges so nothing slips past the mesh.
• Copper mesh in weep holes and damp spots. Does not rust, still lets air through.
• Sheet metal or cement patches for gnawed corners, damaged siding, and rat-sized damage. Cornell IPM names galvanized sheet metal as the durable raccoon-resistant option.
• Concrete, metal, or hardware cloth under porches, decks, and shed floors where rats burrow. Cornell describes a “rat wall” as a buried barrier “one foot deep with a six-inch horizontal shelf at the bottom.”

What does not work on its own:

• Expanding foam alone. Foam fills the gap but a mouse or rat gnaws through cured foam. The foam is the outer cover over a metal or steel-wool plug, not the plug itself.
• Plastic, vinyl, rubber, or wood patches. All gnawable.
• Wadded paper, insulation, or steel wool without a caulk cap on top. It pulls loose, falls out, and becomes nesting material.
• Peppermint oil, mothballs, ultrasonic plug-ins, dryer sheets. Nothing in this category excludes mice, rats, or cockroaches. The EPA’s prevention guidance is food/water/shelter/seal exclusion. There is no aromatherapy exception.

Cut off food and water

The EPA’s Do’s and Don’ts list starts with this section. It is also the section people skip.

• Store food in sealed plastic or glass containers. Pet food counts.
• Garbage in tightly covered trash cans, removed from the home regularly. The EPA rodent-control guidance repeats the tight-fitting lid rule.
• No pet food or water left out overnight.
• Fix leaky plumbing. The EPA singles this out: “Fix leaky plumbing and don’t let water accumulate anywhere in the home.” Cockroaches and silverfish need damp harbourage more than they need crumbs.
• Empty drip trays under house plants and the refrigerator. Standing water indoors grows mosquito populations and feeds anything else that needs a drink.
• Compost covered and turned. Open compost is an outside buffet that pulls rats, raccoons, and flies toward the foundation. The EPA rodent-control page recommends turning compost to cover newly added food scraps.
• Bird feeders. During an active infestation, stop feeding or switch to huskless seed with less residue. Per the EPA rodent-control page, this cuts the steady food source that draws rodents toward the house.

Knock out the harbourage

A pest is more likely to walk up to a sealed crack if there is cover on the way. UC IPM names “hiding places” as one of the four contributors and gives indoor examples: voids under or behind cabinetry, gaps above drop ceilings, and cluttered storage rooms. Outdoors the same logic covers leaf piles against the wall, stacked firewood, and dense ground cover. Pull the cover, and the run-up to your house is exposed.

Inside the home:

• Declutter cardboard, paper, magazines, and stored clothing. The EPA’s Do’s and Don’ts page: “Get rid of things like stacks of newspapers, magazines, or cardboard.”
• Vacuum under and behind appliances where crumbs and pet hair collect.
• Move storage off the basement floor and away from the foundation walls.
• Caulk the gap behind baseboards, around plumbing penetrations under sinks, and along the back of cabinets.

Outside the home:

• Mow a clear band of grass against the foundation.
• Move firewood at least a few feet off the wall and off the ground.
• Pull leaf piles and deep mulch away from the foundation. The EPA rodent-control guidance lists leaf piles and deep mulch as rodent nesting sites.
• Clear gutters so water does not back up against the fascia and create damp soffits.
• Check incoming packages, boxes, groceries, and secondhand furniture before they come inside. The EPA puts this on its Do’s list: pests arrive on purpose or as hitchhikers.

Timing and safety for the seal-up itself

Cornell IPM has two rules that prevent the most common exclusion mistake.

• Do not seal a hole with an animal still inside. “Before closing animal entry sites in a building, be certain that animals will not be trapped inside.” A simple version: stuff the opening loosely with newspaper or tape a piece over it for two to three days. If the paper stays in place, nothing is using it. If it gets pushed out, an animal is still coming and going.
• Mind the season. Spring and summer exclusion can trap juvenile squirrels, raccoons, or bats in a wall void. Cornell: “listen for sounds (such as high-pitched squealing or chirping)” before sealing.

The mistake almost everyone makes

Sealing inside first. The interior gap where the mouse enters the wall cavity is rarely the same gap as the one on the exterior. Seal outside in. Then, after activity stops, close the interior gaps.

The other common failure is using caulk or expanding foam as the barrier instead of as the cover over a non-gnawable plug. A patch that the mouse can chew through is no patch at all. The expansion foam is doing one job, the steel wool is doing the other, and you need both.

Finally, sealing alone is half of the job. The houses that stay pest-free are the houses where sealing got done at the same time as food, water, and harbourage. Either layer by itself slows pests down; both layers together stop them.

When to call a pro

A licensed pest professional or exclusion contractor is the right call when:

• Active pests keep showing up after you have sealed the obvious exterior gaps, fixed plumbing leaks, and removed the harbourage. The entry point is somewhere you cannot reach.
• You have a rat or raccoon issue under a deck, in a crawlspace, or under a slab where buried exclusion work is needed.
• The work is at height (soffits, roofline, second story) or near utilities you should not work around yourself.
• A chimney needs a code-compliant cap and you do not have roof access or a head for heights.
• You have a cockroach or bed-bug problem that has already established indoors. Exclusion slows reinfestation; the existing population needs treatment first.

Ask for an exclusion plan in writing, with a list of the materials used and the gaps closed. The plans that pay off are the ones that walk the building with you and identify each entry point before sealing anything.