Skip to content
OASIS
LivingIQ

Natural Pest Control

Excluding Mice From an Old Farmhouse Without a Single Poison Bait

Trapping is maintenance. Sealing is a fix. Here is the autumn walk-around we do every year, in order.

9 min read Beginner
Detail of a stone farmhouse foundation with sealed gaps and copper mesh

An 1890s farmhouse on a mountainside is a mouse hotel with good views. Our first winter here I caught 41 mice and felt productive. The second winter I sealed the house and caught four.

Poison is the worst option available: it kills the barn owls and black snakes that were doing the job for free, and the mice die inside your walls. Exclusion first, always.

Materials

  • Copper mesh (stuf-fit)
  • Mortar patch or hydraulic cement
  • Expanding foam (as backing only)
  • ¼in hardware cloth
  • Door sweeps

Tools

  • Headlamp
  • Putty knife
  • Caulk gun
  • Tin snips
  • Mirror on a stick

Estimated cost: $70. Difficulty: Beginner.

1.Walk the foundation with a headlamp at dusk

Anywhere a pencil fits, a young mouse fits. Check sill plates, the gap behind the hose bib, dryer vents, the point where every wire and pipe enters. Mark each gap with chalk rather than fixing as you go.

Headlamp inspection of a foundation gap where a pipe enters a wall

2.Pack copper mesh, then seal over it

Mice chew straight through foam and steel wool rusts out. Stuff the void tight with copper mesh, then cap with mortar patch or cement. Foam alone is a decoration.

3.Screen every vent and chimney

¼-inch hardware cloth over crawlspace vents, dryer exhausts and the chimney cap. Larger mesh lets young mice through; smaller mesh clogs with lint and becomes a fire risk on a dryer run.

4.Fix the doors last

Door sweeps and threshold seals close the biggest remaining gap in most old houses. Check by kneeling inside with the lights off in daytime — any daylight you can see is an entrance.

5.Then trap the ones already inside

Snap traps along walls, perpendicular, baited with a smear of peanut butter. Set ten, not two, for one week. After a sealed house, the population is finite and you will be done.

Common questions

What size gap can a mouse get through?
A quarter inch. If a pencil fits, a mouse fits. Seal with copper mesh and mortar or metal flashing, not foam alone.
Do ultrasonic repellers work?
No. Independent testing has repeatedly found no lasting effect. Exclusion and sanitation are what actually work.
How do I control mice without poison?
Seal entry points first, remove food sources second, and use snap traps for the population already inside. Poison risks pets, raptors and dead mice inside your walls.
Ellis Hartwell

Written by

Ellis Hartwell

Twelve years building and rebuilding systems on 28 mountainside acres. Everything published here has run on this property or been documented on site with the owners.

The newsletter

Get the Homestead Dispatch

One letter every other Sunday: what we built this week on the mountain, what failed, and the numbers behind it. No fluff, no sponsored filler.