Shelter · Pests & Wildlife
Exclusion & Sealing
The single most effective step in pest prevention is also the simplest: find the openings and close them. No chemicals, no traps, no ongoing cost. Just a sealed building.
Shelter · Pests & Wildlife
The single most effective step in pest prevention is also the simplest: find the openings and close them. No chemicals, no traps, no ongoing cost. Just a sealed building.
> University extension programs and the EPA agree: exclusion is the foundation of any effective pest management approach.<1, 2 A mouse can fit through an opening the size of a dime. Insects can enter through gaps as small as 1/16 of an inch.3 Most homes have dozens of these openings, concentrated around pipe penetrations, utility entries, door thresholds, and where the foundation meets the siding.
This guide walks through the full exclusion process: inspecting your home inside and out, choosing the right sealing material for each type of gap, doing the work, and maintaining it over time. The materials are inexpensive and widely available at any hardware store. The work is straightforward and requires no specialized skills.
What this guide does not cover: treating an active infestation. If you have rodent droppings in living spaces, visible insect colonies, or evidence of ongoing pest activity, address the infestation first (or call a licensed professional), then seal. Sealing with pests still inside the structure can trap them in walls and create worse problems.4
Walk the full perimeter of your home at the foundation line. Bring a flashlight, a notepad, and a pencil or marker for flagging spots that need attention. You are looking for any gap, crack, or opening that connects the outside to the inside of the structure.
Where the foundation meets the framing is the most common entry zone for mice and insects. Look for cracks in the concrete, gaps where the sill plate sits on the foundation, and openings around anchor bolts.
Every pipe, wire, cable, and conduit that enters the home creates a hole larger than needed. Check around water supply lines, gas lines, electrical conduit, cable and phone lines, dryer vents, outdoor faucets, and HVAC refrigerant lines.5
Check the gap beneath all exterior doors. If you can see daylight under a closed door, pests can enter. Inspect garage door seals along the bottom and sides. Check where the garage meets the house wall.
Attic vents, soffit vents, crawlspace vents, and foundation vents should all have intact screening. Check for torn, rusted, or missing screens. Dryer vents and bathroom exhaust vents should have functional dampers that close when not in use.
Where the roof meets the wall, where fascia boards meet soffit panels, and around chimney flashing. These are common entry points for squirrels, bats, and birds. Inspect safely from the ground with binoculars if needed.
Many entry points are easier to spot from inside, where pipes and wires pass through walls and floors. Work room by room, checking these locations:
Kitchen and bathroom sink cabinets almost always have unsealed pipe penetrations through the back wall or floor. These are direct routes from wall cavities into living spaces.
Pull the stove and refrigerator away from the wall. Check for gaps around gas lines, water lines, and electrical connections. These warm, dark, undisturbed spaces are prime entry and nesting areas.
Check where plumbing stacks, ductwork, and wiring pass through the floor or ceiling. Look for daylight, feel for drafts, and note any gnaw marks, droppings, or rub marks along baseboards and joists.
Water heater closets, furnace rooms, and laundry areas often have unsealed penetrations for fuel lines, flue pipes, condensate drains, and washing machine hookups.
The EPA recommends matching your sealing material to the gap size and location. The best materials for pest exclusion are those that rodents cannot gnaw through: knitted copper mesh, steel wool, cement, hardware cloth, and sheet metal.5 Standard expanding foam alone is not sufficient for rodent exclusion because rodents can chew through it.
Exterior-grade silicone or acrylic latex caulk. Silicone lasts longer and stays flexible; acrylic latex is paintable and easier to clean up. Clean the surface first and remove any old, peeling caulk before applying.3
Cost: $4 to $8 per tube. One tube covers 30 to 50 linear feet of small cracks.
Pack with steel wool or copper mesh first, then seal over with caulk. The mesh prevents rodents from gnawing through; the caulk holds the mesh in place and blocks insects and drafts. Copper mesh does not rust and is the better long-term choice for exterior applications.5
Cost: $5 to $12 for a roll of copper mesh plus caulk.
Hardware cloth with 1/4-inch openings, secured with screws or concrete. Sheet metal or aluminum flashing for flat surfaces. Cement or mortar for foundation cracks. The CDC recommends hardware cloth, lath screen, or metal sheeting for larger holes, cut to fit around pipes where needed.6
Cost: $8 to $15 for a small roll of hardware cloth.
Replace worn door sweeps on all exterior doors, including the door between the garage and the house. Choose heavy-gauge aluminum or stainless steel sweeps for garage service doors. The sweep should compress against the threshold with no visible gap when the door is closed.
Cost: $8 to $25 per door sweep.
Replace damaged window screens. Cover attic, soffit, and crawlspace vents with hardware cloth (1/4-inch mesh for rodent exclusion, finer mesh for insect exclusion). Secure with screws, not staples. Install chimney caps where needed.
Cost: $5 to $20 per vent or screen.
Work systematically. Start at the foundation and move upward. Complete one side of the house before moving to the next. This prevents missed spots and helps you track what has been done.
Wear work gloves when handling steel wool, copper mesh, or hardware cloth. The metal filaments can cause cuts. Wear eye protection when using expanding foam overhead. Use a stable ladder for any work above ground level, and do not attempt roofline work from a ladder if you are not comfortable at height.
If you encounter rodent droppings during the inspection, do not sweep or vacuum them. Dampen the area with a disinfectant solution (1 part bleach to 10 parts water), let it soak for five minutes, then wipe up with paper towels while wearing gloves. This prevents aerosolizing potentially contaminated dust.6, 7
For medium-sized gaps around pipes and conduit, this two-layer approach is the standard recommendation from extension and EPA sources:
Cut a piece of copper mesh or steel wool slightly larger than the opening.
Use a screwdriver or putty knife to pack the mesh tightly into the gap, recessing it slightly from the surface.
Apply exterior-grade caulk or pest-resistant expanding foam over the mesh, smoothing it flush with the surface. The caulk holds the mesh in place and blocks insects and air; the mesh prevents rodents from gnawing through.
Exclusion is not a one-time project. Buildings settle, caulk cracks, foam shrinks, and weather opens new gaps. Check your work after the first rain, the first hard freeze, and at least once per season. An annual perimeter walk in late summer or early fall, before cooler weather drives pests to seek shelter, is the minimum maintenance schedule.
Replace any caulk that has cracked or separated. Re-pack any mesh that has been dislodged. Check door sweeps for wear. Inspect screens for new tears. If you notice signs of new pest activity (droppings, gnaw marks, rub marks along baseboards), investigate the area for an entry point you may have missed.
You cannot modify the building, but you can address many exclusion gaps without permanent changes. Door sweeps that slide onto the bottom of the door (no screws) are available for under $15. Removable caulk or weatherstripping tape can seal window gaps. Under-sink pipe gaps can be stuffed with copper mesh without drilling or adhesive.
For structural issues that require permanent repair (foundation cracks, damaged vent screens, broken window frames), document the problem in writing and request your landlord make the repair. In most jurisdictions, landlords have a legal obligation to maintain habitable conditions, and pest entry points fall within that scope.
See Renters and Small Spaces for the broader picture on renter preparedness.
Standard polyurethane foam is not a rodent barrier. Mice and rats can gnaw through it quickly. Foam works as a weatherseal and insect barrier, but rodent-grade gaps need copper mesh or steel wool underneath.
Closing entry points with rodents still inside the structure can trap them in wall cavities, where they die and create odor problems. Address the current population first, then seal.
The door between the garage and the house is often the weakest link. If the garage door seal is worn, pests enter the garage easily. If the interior door has no sweep, they walk straight into the house.
Steel wool rusts when exposed to moisture. In exterior applications, use copper mesh instead, or cover steel wool with caulk immediately to protect it from the elements.5
A thorough inspection identifies all the entry points before you start. Sealing three obvious gaps while missing the pipe penetration behind the water heater means the pest problem continues through the opening you did not find.
The exterior layer: landscaping, drainage, and food sources that attract pests to the building.
Motion lighting and physical barriers that discourage wildlife from settling near the home.
Weatherproofing work that keeps both weather and pests out of the structure.
A broader room-by-room inspection covering doors, windows, alarms, utilities, and more.