Old houses are why people move to Mercer County and old houses are why we’re busy in November. A brick rowhouse in Trenton’s Mill Hill, a fieldstone colonial off Nassau Street in Princeton, a Victorian on Broad Street in Hopewell Borough or a 1920s four-square in Ewing all share a problem their owners rarely think about until the first cold night: a century’s worth of openings, most of them small, most of them invisible from the sidewalk, and every one of them a door for mice. This is what rodent-proofing an older home actually involves, and why it’s a different job than sealing a newer one.
Why older houses leak mice
A mouse needs a gap about the width of a pencil. A house built before the Second World War has hundreds of them. Brick and stone foundations laid with lime mortar have joints that have crumbled a little every winter for a hundred years. Coal chutes and basement windows were bricked over decades ago and never properly sealed. Balloon framing in many pre-1930 houses means the wall cavities run straight from the basement to the attic, so a mouse that gets in at the sill is in the bedroom wall by morning. Plumbing, gas and electric were all added later, each through its own hole. Porches and additions meet the original house at seams. And in the rowhouses of Trenton and the twins of Chambersburg, the basements and walls are shared, so the mouse problem is the block’s, not yours.
None of this is a reason to panic and none of it is unfixable. It’s just a longer list than the one for a 1995 colonial in Robbinsville.
Where we look on an older house, from the ground up
The foundation and sill. We walk the entire perimeter at ground level with a light, looking at every mortar joint, every old window well, every bricked-over opening, and the gap where the wooden sill sits on the stone or brick. On the historic houses in Princeton, Pennington and Hopewell this is where most of the entry points are, and they’re often hidden by foundation plantings and mulch piled against the wall.
Penetrations. Every place a pipe, wire or line comes through: the gas meter, the electrical service, the AC line set, the hose bibs, the dryer and bath vents, the cable and fiber drops, the old oil fill pipe nobody uses. On a house that has been renovated three or four times, there are usually a dozen of these and half have never been sealed.
Doors and garages. Original wood doors on old houses rarely seal at the bottom, and detached garages and carriage houses in the boroughs are essentially open to mice. The garage-to-house door and the bulkhead door to the basement are two of the biggest openings on the property.
The roofline. Mice climb. Soft fascia, unscreened gable vents, the gap where a porch roof meets the wall, all the spots squirrels and raccoons use, are mouse entries too, and after a wildlife job they’re the main ones.
Inside. Basements, crawlspaces, the back of the kitchen cabinets where the plumbing comes through, behind the stove and refrigerator, the attic. We’re reading droppings, rub marks and gnawing to find the runways, because that’s where the traps and stations go.
Sealing an old house without wrecking it
Rodent-proofing a historic home means closing gaps with materials mice can’t chew through, in a way that doesn’t trap moisture in old masonry or show from the street. We use copper mesh or steel wool packed into the gap and backed with a sealant that’s appropriate for the surface, hardware cloth over vents and larger openings, metal flashing at rooflines, and proper door sweeps and garage seals. We don’t use expanding foam as the primary fix, because mice chew through it, and we don’t use mortar mixes that are harder than the original on soft old brick, because that causes damage of its own. The goal is a house that’s closed to rodents and still looks like a hundred-year-old house.
Trenton, specifically
Rowhouses are the hardest rodent job in the county and the one most worth doing right. In Mill Hill, Chambersburg, the West End and the South Ward, the houses share walls and often basements, and a mouse or rat population moves through a block the way it would move through one big building. Treating one unit buys a few weeks. What works is sealing your unit thoroughly, treating the shared basement, and, wherever possible, coordinating with the neighbor so both sides get done. We do that regularly for Trenton homeowners and landlords, and a plan with unlimited callbacks is the honest recommendation there, because in attached housing the pressure never fully goes away.
Ewing, Hamilton and the post-war stock
Not every older house is a century old. The ranches, capes and split-levels of Ewingville and West Trenton in Ewing, and Mercerville, Hamilton Square and Yardville in Hamilton, are sixty to seventy years old now, and they fail in a predictable set of places all at once: the garage door bottom seal, the original soffit vents, the seam where a 1970s addition meets the old foundation, and the crawlspace vents that lost their screens. The list is shorter than on a Victorian but the houses are closer together, so a problem on one street becomes the neighbors’ problem quickly.
The boroughs
Hopewell Borough, Pennington and Hightstown are small towns of big old houses on tight lots with barns, carriage houses and detached garages behind them, and those outbuildings are where the mice winter before they move into the house. Rodent-proofing here usually means the outbuildings too, and it usually turns up a squirrel or bat issue at the roofline while we’re at it; our Hightstown and Hopewell Borough pages cover what we run into most in each.
What the plan adds
Sealing an old house is the big step, and it’s a one-time cost quoted after a free inspection. What keeps it sealed is a plan. Our Comprehensive Rodent & Pest Defense Plan, from $65 a month, includes mice with interior stations placed as needed, exterior rodent stations as an add-on, four seasonal visits inside and out, and unlimited callbacks between visits. On an older home that matters more than on a new one, because old houses keep opening new gaps: mortar keeps weathering, wood keeps softening, and someone needs to be walking the foundation every season. It also covers the ants, roaches, spiders and pantry pests that old basements and kitchens get, and carpenter ants and stinging insects at the roofline. Details are on the plans and pricing page, and the full description of what a rodent control visit involves is on the service page.
Before we get there
Pull mulch and plantings back from the foundation so the sill is visible. Move firewood off the ground and away from the house. Put birdseed, pet food and grass seed in sealed bins. Replace the garage door seal if you can see daylight. Look under the kitchen sink and behind the stove for droppings so you can tell us where the activity is. And if you’re hearing scratching at the roofline as well as in the walls, say so, because that changes the visit; the exclusion work at the top of the house is usually where a mouse problem in an old home actually started.
Questions we get about this
Will sealing an old house trap moisture in the walls?
Not if it’s done correctly. We seal the gaps rodents use, not the vents and weep paths the house needs to breathe, and on old masonry we use materials that don’t trap water against soft brick. On a house that has real moisture problems in the basement we’ll tell you, because damp is also what draws the ants and roaches that old basements get.
My house is in a historic district. Will the work be visible?
It shouldn’t be. Copper mesh and sealant in a mortar joint, hardware cloth behind a vent louver and metal flashing tucked at a roofline are all designed to disappear. Where the real fix is replacing rotted wood, we’ll point it out so you can have a carpenter match the original profile.
Do you treat the rowhouse next door too?
If the neighbor agrees, gladly, and in Trenton we often end up doing two or three attached units the same week. When that isn’t possible we seal your unit as thoroughly as we can, treat the shared basement where we have access, and recommend a plan with unlimited callbacks, because in attached housing the pressure comes back from next door.
Is it worth rodent-proofing if I’m selling the house?
Yes. Droppings in the basement are one of the first things a home inspector notes, and a clean inspection is worth more than the sealing costs. We can also provide the termite and wood-destroying insect inspection report most Mercer County closings require on the same visit.
Call 609-356-PEST (7378) or request a free inspection. We’re based in Lawrence Township and we’ve been inside more old basements in Mercer County than we can count. The inspection is free, the estimate is written, and we’ll tell you the least you need to do to close the house for good.