The gap is smaller than you think
House mice can squeeze through openings as small as a quarter-inch — roughly the diameter of a standard pencil. Their skeleton isn't rigid; a mouse can compress its ribcage to fit through a gap that looks, to a person, like it couldn't possibly admit anything alive. Norway rats and roof rats need more room, typically a half-inch to a full inch, about the size of a quarter. That's still small enough that most homeowners walk past the actual entry point dozens of times without noticing it.
This is the first thing that trips people up when they try to solve a rodent problem themselves: they look for something dramatic — a hole in the wall, a gap under the door — and miss the actual access points, which are almost always smaller and less obvious.
Where rodents actually get in
After inspecting thousands of properties, a handful of entry points show up again and again:
Utility penetrations. Anywhere a pipe, wire, or vent passes through an exterior wall, there's typically a gap around it from the original construction. Plumbers and electricians cut the hole to fit the pipe or conduit, not to be rodent-proof, so there's almost always a quarter-inch to half-inch gap left around the penetration. This is consistently one of the most common entry points found on inspections.
Foundation and siding gaps. Houses settle. Concrete cracks. Siding shifts slightly over years of expansion and contraction. None of these gaps need to be large — a settled foundation crack a quarter-inch wide is a functioning mouse door.
Garage door gaps. The rubber seal along the bottom of a garage door degrades over time, and most garage doors were never a tight seal to begin with. A gap of even a half-inch along a 16-foot-wide door is a lot of linear opportunity.
Roof and attic access. Roof rats in particular are excellent climbers. Gaps where the roofline meets the wall (soffit gaps), damaged or missing vent screens, and gaps around the chimney flashing are all common attic entry points that homeowners rarely inspect because they require getting on a ladder or into the attic itself.
Dryer vents and other vent lines without proper covers. A vent line with a damaged or missing flap, or a screen that's rusted through, is effectively an open door.
Why steel wool and caulk alone usually don't solve it
Steel wool stuffed into a gap is a legitimate short-term deterrent — rodents generally won't chew through it, at least not quickly. But it's rarely a complete fix for three reasons. First, most homeowners find and seal the one or two entry points they can see, while missing the others, and a rodent population only needs one working entry point to keep coming in. Second, steel wool degrades with moisture and can rust out over a season or two, especially at exterior grade-level gaps. Third, caulk that isn't paired with a rigid backing (like steel wool or hardware cloth behind it) can simply be gnawed through, since caulk alone has no resistance to a rodent's teeth.
A proper exclusion job pairs a rigid barrier material with a sealant, and — critically — is based on a full exterior inspection rather than sealing whatever's visible from eye level at the front of the house.
What a real inspection actually covers
A thorough rodent inspection walks the entire perimeter of the structure at ground level, checks the roofline and any accessible attic space, and traces every utility penetration and vent. It also looks for signs of existing activity — droppings, gnaw marks, grease trails along baseboards or beams, and nesting material — to determine whether exclusion alone will solve the problem or whether there's already an active population indoors that needs to be trapped out first.
This matters because sealing every entry point on a house with an active indoor rodent population doesn't remove the rodents already inside — it just locks them in. The correct sequence is almost always: identify and address active indoor activity first, then seal entry points, then monitor to confirm the exclusion held.
Do electronic or ultrasonic repellers work?
This comes up often enough to address directly. Ultrasonic pest repellers are a large product category, and the evidence for their effectiveness on established rodent populations is weak at best — most studies find rodents habituate to the sound within days and the effect doesn't hold up in real-world conditions with walls, furniture, and multiple rooms breaking up the sound waves. They're not a substitute for physical exclusion. If a product promises to solve a rodent problem without addressing the actual entry points, that's worth being skeptical of.
What this costs and what to expect
Exclusion work is typically priced by the scope of the job — how many entry points need addressing and how accessible they are — rather than a flat rate, since a single-story home with a few utility gaps is a very different job from a home with attic access issues and a compromised foundation. A written, itemized quote before any work starts should specify exactly what's being sealed and where, so there's no ambiguity about what you're paying for.
If you're hearing scratching in the walls or attic, finding droppings, or just want a professional inspection before winter pushes rodents indoors looking for shelter, we walk the property, show you what we find, and quote the work honestly before anything happens.