Short answer
Walk the entire exterior and interior of your home, looking for any gap the size of a pencil or larger. Seal those openings with rodent-proof materials: copper or stainless steel mesh, 1/4-inch hardware cloth, sheet metal, mortar/hydraulic cement, and high-quality exterior sealants. Add door sweeps, weatherstripping, and pest-proof vent covers. Avoid relying on spray foam alone.
Mice: fit through gaps ≥ 1/4 in (6 mm)
Rats: fit through gaps ≥ 1/2 in (12 mm)
Recommended exclusion mesh: 1/4 in (6 mm) galvanized or stainless hardware cloth
Sheet metal: 26–22 gauge for patching
What to look for and why it matters
Rodents follow edges and squeeze through tiny openings near food, warmth, and shelter. Typical entry points include utility penetrations, garage door bottoms, door thresholds, dryer and attic vents, roofline gaps (soffit/fascia), foundation cracks, and under-sink pipe chases. They leave clues: droppings, greasy rub marks, gnawing, shredded insulation, and burrow holes along foundations.
Tools and materials
- Inspection gear: bright flashlight or headlamp, mirror, smartphone camera, chalk/marker, tape measure
- PPE: nitrile gloves, cut-resistant work gloves, eye protection, N95/P100 respirator for cleanup, long sleeves
- Hand tools: utility knife, aviation snips, tin snips, shears, drill/driver with self-tapping screws, hammer, caulk gun
- Ladders: step ladder, extension ladder (with stabilizer for gutters)
- Sealants and barriers:
- Copper mesh or stainless steel wool (won’t rust)
- 1/4-inch galvanized or stainless hardware cloth
- Exterior polyurethane or high-quality silicone sealant (paintable where needed)
- Mortar or hydraulic cement for masonry cracks
- Pest-resistant expanding foam (as a backing only, not standalone)
- Sheet metal (26–22 ga) for larger holes
- Door sweeps (brush or rubber), garage door bottom seals, weatherstripping
- Pest-proof vent covers (dryer, foundation, soffit/gable)
Estimated cost: $60–$200 in materials for most homes. Time: 2–6 hours for a thorough first pass.
Step-by-step: Inspect and seal
1) Prepare and stay safe
- Disinfect droppings/urine before handling: spray with a disinfectant (or 1:10 bleach solution), let sit 5–10 minutes, wipe with disposable towels. Don’t sweep or dry-vac droppings.
- Wear gloves and a respirator if cleaning contaminated areas. Wash hands after.
- Practice ladder safety and avoid roof work in wind or rain.
2) Exterior inspection (ground to roof)
Walk clockwise around the house during daylight, then again at dusk with a flashlight to spot gaps and rub marks.
- At the foundation/siding line: gaps where siding meets masonry; missing or chewed corners
- Utility penetrations: A/C lines, gas pipes, cable/phone, electrical conduit
- Vents: dryer hood (stuck flapper), crawlspace/foundation vents, gable/soffit vents
- Doors: gaps under exterior and garage doors; check daylight at the threshold
- Windows and window wells: torn screens, rotted sills
- Brick weep holes: must remain open for drainage but can be rodent-guarded
- Roofline: loose soffit/fascia, attic intake vents, chimney crown/cap, plumbing stacks
- Yard clues: burrows at slab edges, under stoops, near HVAC pads or decks
Mark each issue with chalk or painter’s tape as you go.
3) Interior inspection
Focus on warm, hidden pathways:
- Kitchen/laundry: behind stove, fridge, dishwasher; around sink and washer hookups
- Mechanical room: pipe and wire penetrations around water heater, furnace, boiler
- Basement/garage: rim joist gaps, sill plate cracks, door seals, floor-to-wall joints
- Attic: around eaves, wiring and pipe penetrations, attic hatch
Use your phone to record video behind appliances you can’t pull out.
4) Seal by opening type
- Small gaps (< 1/4 in): high-quality exterior sealant may suffice. For longevity, back with mesh where feasible.
- Medium gaps (1/4–1 1/2 in): tightly pack copper mesh or stainless steel wool, then cover with polyurethane sealant or mortar. Use foam only as a filler beneath a chew-proof layer.
- Large holes: cut 1/4-in hardware cloth or sheet metal to overlap by 1–2 inches. Fasten with screws and washers or masonry anchors; seal edges with caulk.
- Utility penetrations: split a short length of copper mesh around the pipe, pack, then caulk. For larger sleeves, add a sheet metal escutcheon.
- Vents:
- Dryer: replace with a metal louvered hood that closes tightly. Do not put fine mesh over the outlet (lint/fire risk).
- Gable/soffit: add 1/4-in hardware cloth behind decorative louvers.
- Doors and garages: install brush or rubber door sweeps; adjust strike plates; add garage bottom and side seals. Consider a threshold for uneven slabs.
- Masonry/foundation: fill cracks with hydraulic cement; for larger voids, mortar over mesh.
- Brick weep holes: insert stainless weep covers or loosely pack copper mesh to allow drainage and airflow; never mortar shut.
- Chimney: fit a chimney cap with appropriate mesh; consider a pro for safe installation and code compliance.
Tips for best results
- If you see daylight, air, or water intrusion, rodents can likely use it—seal it.
- Trim vegetation 12–18 inches away from walls; elevate firewood; reduce clutter in garages.
- Coordinate trapping indoors for 1–2 weeks before final sealing to avoid locking rodents inside. Snap traps in tamper-resistant stations are effective.
- Use tracking powder (flour or talc) near suspected gaps overnight to spot footprints.
- Recheck seasonally; freeze-thaw cycles and settling can open new routes.
Common mistakes
- Using spray foam by itself—rodents chew through it.
- Blocking required ventilation or combustion air intakes.
- Sealing brick weep holes solid.
- Ignoring the garage and door thresholds.
- Not fixing stuck dryer flappers and damaged vent hoods.
When to call a professional
- Persistent activity after your exclusion and trapping efforts
- Noises in walls/attic you can’t safely access, or roof/chimney work at height
- Significant structural damage or large foundation/roof gaps
- Suspected sewer rats entering via drains (plumber may install guards/backwater valves)
- Wildlife species (bats, squirrels, birds) that have legal protections and specific exclusion windows
With a careful inspection, the right materials, and a methodical seal-up, most homeowners can dramatically reduce rodent entries in a weekend and keep them out long-term.