The Mouse Callback Traced to a Garage Door Corner

Why this matters

A third visit to the same mouse job is where a customer stops believing the shop and starts calling someone else. In this case the first two visits were not wrong: the exterior gaps the tech sealed were real gaps, and the traps were in the right places. The house kept catching mice anyway, because the opening that mattered was one the exterior survey treated as closed. Being right about the walls was not enough when the mice were coming through the garage.

The job so far

A two-story house with an attached two-car garage. The kitchen sits on the far side of the wall the house shares with the garage, with the sink and dishwasher in a run of base cabinets along that wall.

Visit 1. The customer had heard scratching in the kitchen and found droppings under the sink. Lee, the tech, did a full exterior inspection and sealed what he found: a gap around the air conditioning line set where it entered the wall, a gap behind the dryer vent hood, and two spots where siding stopped short of the foundation. He set snap traps along the kitchen base cabinets and under the sink. Four mice were caught over the following week.

Visit 2, two weeks after the first. Two more mice had been caught. Lee rechecked every exterior seal; all were intact and none showed fresh gnawing. He reset the traps, told the customer a few mice already inside were expected, and wrote it up.

Visit 3, five weeks after the first. Three more mice in the kitchen traps, nine in all. The customer called the office and asked for someone other than Lee. The office sent Lee anyway, with the route lead's agreement, because he knew the house.

The third visit

CUSTOMER: That's nine mice. You sealed the house twice.
TECH: The outside walls are still sealed. I checked
      every spot before I came in. If they were coming
      through the walls I'd see chewing on the seals.
CUSTOMER: So where are they coming from?
TECH: That's what today is for. Can I start in the
      garage? Your kitchen backs right onto it.
CUSTOMER: The garage door's always shut.
TECH: Shut isn't the same as sealed at the corners.
      Mind if I close it and turn the lights off in
      there for a minute?
CUSTOMER: Go ahead. What are you looking for?
TECH: Daylight at the bottom. A mouse needs about a
      quarter inch.

Following the droppings back

Lee started at the problem end and worked outward, which is the order that keeps the trail honest.

Under the sink. Fresh droppings, dark and soft-looking, along the back of the base cabinet where the cabinet floor met the wall. Behind the dishwasher, with the kick plate off, there were more and a smear of grease on the bottom edge of the drywall. The drywall behind the cabinets stopped short of the subfloor with a gap at the wall base he could get a finger into. That is the house side of a path, not the source.

The garage side of that wall. In the garage, steel shelving stood against the shared wall. On the bottom shelf were an open bag of birdseed and a bag of grass seed, both chewed open at the corners. Droppings were on the shelf, on the slab under it and along the base of the wall. The garage drywall ended about an inch above the slab along that wall, which is common so the board does not wick water, and behind the shelving the gap opened into the wall cavity.

So mice were feeding in the garage and using that wall as a route into the kitchen. That still did not say how they were getting into the garage.

Across the garage. Lee followed the droppings along the base of the shared wall, then along the front wall to the left side of the overhead door, where they were heaviest in the last foot before the jamb. He closed the door, turned off the garage lights and stood inside.

Daylight showed at the left corner. The bottom seal, the rubber strip along the bottom of the door, had been chewed back from the jamb right where the slab dipped. This is the corner as Lee saw it from inside:

 left jamb    closed door, seen from inside
 |  |
 |  |  door panel, bottom edge
 |  |-------------------------------------------
 |  |  daylight  |#### rubber bottom seal #######
 |  |  1/2 in    |###############################
 |  |____  ______|_______________________________ slab
 |  |    \/  slab dips at the corner
 |  |<-- 2 in -->|  seal chewed back from the jamb;
 |  |               the rest still meets the slab

A 1/2 inch gap is twice what a mouse needs and enough for a rat. Fresh gnaw marks on the cut edge of the rubber and droppings on the slab right inside the gap settled it.

Why the first two visits missed it

The exterior survey had looked at the door from outside in daylight: door down, bottom seal visible, nothing obvious. From outside, a chewed corner sits in the shadow of the jamb and the trim, and a 1/2 inch gap at a dipped slab corner reads as part of the slab line. The check that finds it is from inside the closed garage with the lights off, looking for daylight at both bottom corners and along the jamb weatherstrip.

The second visit was a recheck of the first visit's work. It confirmed that what had been sealed was still sealed, which was true, and that confirmation is what made the garage feel ruled out without anyone having looked at it.

And the garage had food. Birdseed and grass seed on an open bottom shelf gave mice a reason to come in and stay, and the kitchen wall gave them a route to the rest of the house. A mouse that can feed in the garage and nest in a wall cavity will keep turning up in the kitchen traps however well the outside walls are sealed. See related: Mouse and Rat Foraging Range and Trap Spacing.

What Lee fixed

Safety first at the door. Before working at the bottom of the door, Lee unplugged the garage door opener so nobody could run the door onto him, and kept his hands off the bottom brackets, cables and springs: on many doors the bottom bracket holds the lift cable under spring tension, and loosening it releases that energy. Replacing a bottom seal does not involve the bracket. Anything involving springs, cables, track or opener adjustment goes to a garage door company.

The door seal. He slid out the damaged bottom seal and fitted a new one along the full width. At the dipped left corner he added rodent-resistant material behind the seal where it meets the jamb, so the corner closes against the slab rather than relying on rubber alone. The methods, materials and corner details belong to sibling cards: see related: How to Seal a Garage Door Against Rodents, and Rodent Exclusion Materials and Opening Sizes.

Restoring the door. He plugged the opener back in and ran the door through a full close and open cycle. With the door closed and the lights off, he checked both corners and the full bottom edge for daylight; there was none. He then ran the opener's own safety check the owner's manual describes for the photo eyes, and the door reversed as it should. A seal that holds the door up off the floor or changes how it closes is a reason to stop and call the garage door company, not to adjust the opener.

The wall. He packed the gap at the base of the garage drywall behind the shelving with rodent-resistant material and sealed it, and did the same at the drywall gap behind the dishwasher on the kitchen side. Sealing a wall with mice possibly inside means traps go on both sides of it, which he did.

The food. He asked the customer to move the seed into lidded metal containers and off the bottom shelf. She did it before he left.

The droppings. Before setting new traps he cleaned out the old droppings under the sink, behind the dishwasher and on the garage shelf, wearing gloves and a respirator, wetting them with disinfectant first and wiping them up rather than sweeping or vacuuming, which puts dried rodent droppings into the air, as the CDC's cleanup guidance describes. Clean surfaces mean any dropping found on the next visit is new.

Monitoring. Traps along the kitchen cabinets and under the sink as before, two in the garage along the shared wall and two near the door corner. A thin patch of unscented talc on the slab inside the door corner and at the garage wall gap, so any traffic would leave tracks.

The service record listed every point sealed, the trap layout, the seed moved, and the photos of the chewed seal and the daylight at the corner.

How the next visits confirmed it

Ten days later. No catches in the kitchen. One mouse in a garage trap along the shared wall: most likely one already living in the garage when the door was sealed, which is why traps went in there. No fresh droppings on the cleaned surfaces in either room, no tracks in either talc patch. Lee checked the door corners from inside with the lights off again: no daylight, no new gnawing on the new seal.

Three weeks after that. No catches anywhere, no droppings, clean talc. Lee pulled the traps from the kitchen, left two in the garage as monitors on the customer's quarterly service, and closed the callback.

The customer's total was nine mice before the door was found and one after. Ten mice, all told.

What would have pointed elsewhere

• Gnawing on one of the exterior seals from visit 1. The seal itself had failed, and the work goes back to that spot and the material used there.
• Droppings heaviest in the attic or at the top of the kitchen wall. Mice moving down from above suggests a roof-line or soffit entry, and the inspection goes up. See related: How to Inspect an Attic for Rodent Activity.
• No droppings in the garage at all. The garage drops out, and the plumbing and utility penetrations under the sink and behind appliances come next. See related: How to Seal Pipe and Utility Penetrations With Mesh.
• A clean door corner but food in the garage. Something else is letting mice into the garage, usually a side door threshold or a gap at the door jamb weatherstrip higher up.

Where callbacks like this go wrong

Rechecking instead of re-inspecting. A callback that only confirms the first visit's work cannot find what the first visit missed. On a second callback, inspect as if new.

Trapping harder. More traps in the kitchen would have kept catching mice from the garage for as long as the seed lasted.

Calling the garage outside the job. The attached garage is part of the structure the mice are using. If it is not in the inspection, the inspection is incomplete.

References

• See related: How to Seal a Garage Door Against Rodents
• See related: Rodent Exclusion Materials and Opening Sizes
• See related: Mouse and Rat Foraging Range and Trap Spacing
• See related: How to Set Snap Traps Along a Rodent Runway
• CDC guidance on cleaning up after rodents