Pest Control Experts Share the Entry Points They Check in Every Old Home

A house built in 1965 has been through sixty winters, sixty summers, and decades of freeze-thaw cycles that slowly pull materials apart at the seams. Wood framing shrinks as it dries over time, concrete settles unevenly, and original caulk and mortar become brittle and crumbly. What started as a tight joint becomes a gap wide enough for a mouse to squeeze through. Pest control professionals approach older homes as a different category of problem entirely. The structural movement isn't a flaw in the original construction — it's just what happens to any building over a long enough timeline. But that movement creates conditions that newer homes with synthetic framing materials and modern sealants don't face in the same way. Wood, in particular, is a pest magnet in two directions. It deteriorates in ways that create physical gaps, and it also attracts wood-boring insects like carpenter ants and termites that widen those gaps further. A small crack that lets in moisture accelerates rot, which invites more insects, which creates bigger openings. Pest professionals call this the "cascade effect" — and it's why older homes require a more systematic inspection approach than a quick walk-around can provide.

Every pest inspection of an older home starts at ground level, and for good reason. The foundation is where the structure meets the soil — and where decades of settling create the most reliable entry points for rodents and insects. Pest professionals walk the perimeter looking for cracked mortar joints, gaps around utility conduits, and places where the sill plate has pulled away from the foundation wall. The pencil-width rule is the field standard: if a standard pencil fits into a crack or gap, a mouse can compress its body to fit through the same space. It sounds almost impossible, but mice have collapsible rib cages that allow them to squeeze through openings as small as a quarter inch. That means a crack that looks cosmetic to a homeowner reads as a doorway to a rodent. Conduit penetrations — where electrical lines, gas pipes, or cable runs enter the foundation — are especially common problem spots in homes built before 1980. Installers often drilled oversized holes and filled the gaps with materials that have long since crumbled. Pest pros also flag areas where the concrete parge coat (the thin outer layer applied to block foundations) has chipped away, exposing the porous block underneath. Rodents can gnaw through porous concrete block far more easily than most homeowners expect.

Most homeowners spend their pest-prevention energy at eye level — checking door sweeps, looking under sinks, examining the garage. Pest control professionals say that focus leaves the most active entry points completely unaddressed. In homes over 40 years old, the roofline is often where the real action is happening. Soffit panels made from the original pressed wood or aluminum have a lifespan. When they deteriorate, they pull away from the fascia board and leave gaps wide enough for a squirrel to walk through without slowing down. Ridge vents from the 1970s and 1980s were often installed without the fine-mesh backing that modern versions include, making them essentially open doors for wasps and bats. The junction where a roofline meets a chimney is another classic weak point — the flashing shifts over time, and the gap that opens up is exactly what a bat colony needs to establish a roost. Bats are the pest that surprises most homeowners in this category. A colony can enter through a gap as small as three-eighths of an inch, and once established in an attic, they're protected under federal law during maternity season, which limits when removal can legally happen. Pest pros recommend binoculars at dusk as a simple way to watch for bat activity before investing in any roofline repairs.

Wherever a pipe enters an old home through a wall or floor, there's a seal around it — and in homes built decades ago, that seal has almost certainly failed. The foam and caulk used in original construction dries out, shrinks, and cracks over time, leaving a gap between the pipe and the surrounding wall material. Pest professionals check these spots routinely because they're almost always productive. Under the kitchen sink is one of the most consistent finds. The drain pipe and supply lines pass through a cabinet floor, and the hole is usually cut larger than necessary. Over the years, the original escutcheon plate (the decorative cover ring) loosens or gets removed entirely, leaving an open gap at floor level — right where mice travel. Behind the washing machine hookup is another reliable spot, especially in older homes where the laundry area was added after original construction and the wall penetrations were never finished properly. Outdoor hose bibs are easy to overlook because they're outside, but the pipe passes through the exterior wall, and gaps around that penetration are a direct route into wall cavities. Pest pros note that these spots often show signs of mouse activity — droppings, nesting material, or gnaw marks on the surrounding wood — even when the homeowner has never noticed a rodent inside the living space.

Weatherstripping from the 1970s and 1980s was typically made from foam or rubber that had a useful life of 10 to 15 years. In a home that's 40 or 50 years old, that original material has long since compressed, cracked, or fallen away entirely. The door still closes and latches, so it feels secure — but the seal against the frame is gone. Pest professionals use a simple flashlight test that homeowners can do themselves: on a bright day, stand inside a closed room with the lights off and have someone shine a flashlight slowly around the exterior door and window frames from outside. Any light that bleeds through is a gap large enough for insects and, in some cases, small rodents. Wood door thresholds are a particular problem — they warp and cup over time, leaving a visible arc of daylight across the bottom of the door that weatherstripping alone can't bridge. Window frames in older homes often show the same pattern. Original wood frames have pulled slightly away from the surrounding trim as the house settled, and the gaps along the top and sides of the frame are often hidden behind interior trim or exterior caulk that looks intact from a distance but has cracked through. Ron Harrison, an entomologist with Orkin Pest Control, notes that mice are drawn specifically to spots where light penetrates — which is exactly why those frame gaps are so reliably exploited.

Finding the entry points is the straightforward part. Sealing them in a way that actually holds is where homeowners often fall short — not from lack of effort, but from using the wrong materials for the job. Expanding foam is the most commonly reached-for fix, and for insects it works reasonably well. Against rodents, it's nearly useless. Mice and rats can chew through cured expanding foam in minutes. Pest professionals use copper mesh or steel wool packed tightly into gaps first, then cover it with hydraulic cement for foundation cracks or silicone caulk for frame gaps and penetrations. The metal mesh physically blocks gnawing, and the sealant over it eliminates the light and airflow that attract pests to the spot in the first place. For gaps larger than half an inch — around conduit runs or where a sill plate has shifted — hardware cloth (a rigid galvanized mesh) cut to size and secured with screws gives a permanent barrier that no rodent will work through. Greg Baumann, Vice President of Technical Services at the National Pest Management Association, puts the bigger picture plainly: even the best sealing work gets undermined if other entry habits aren't addressed. A professional inspection runs between $100 and $300 for most homes and is worth scheduling before a full sealing project, since pros often find gaps that a homeowner's walk-around misses entirely.