"I could hear scratching in the evening, always in the same spot, over by the dishwasher. We emptied everything, every cupboard, nothing. It was only when we took the plinth off the sink unit that we saw the droppings and the hole around the pipe." This resident of Champigny-sur-Marne spent three weeks hunting for her mice exactly where everyone always looks: in the pasta and flour cupboards. They were living forty centimetres away, in a space no one had reached into since the kitchen was installed in 2011.
A modern fitted kitchen is not a room: it is an assembly of carcases standing on adjustable legs, with a continuous gap of 8 to 12 cm beneath the base units, closed off by a clip-on plinth. Add the oven housing, the dishwasher base, the back of the fridge and unsealed pipe penetrations, and you have the best harbourage a mouse could hope to find in a house: warm, completely dark, never disturbed, and less than a metre from food.
This blog has already covered insulated loft spaces, cellars and their air vents, garden outbuildings, sealing materials and mechanical trapping. This article tackles a distinct subject: the service void of the fitted kitchen, how to inspect it in practice, and how to seal it without dismantling the kitchen.
Why the kitchen, and why late October
Three factors come together at this time of year in Val-de-Marne.
Residual heat from appliances. A fridge compressor, the rear grille of a freezer, a dishwasher motor and an oven housing all give off heat, either constantly or repeatedly. Behind a fridge it is not unusual to measure 25 to 30 °C at compressor level. When night-time temperatures drop below 8 °C — as they have across the Île-de-France region since mid-October — that difference becomes a powerful signal for a house mouse (Mus musculus) that until then had been living in the garden, the garage or the hedge.
The heating coming back on. It reactivates air movement in ducts and service voids, creating warm currents that guide rodents indoors. We have discussed this in relation to ducting and sub-floor voids; the kitchen is the most frequent arrival point, because that is where the water supply, the waste pipe, the gas and the electrics all converge.
Food available with no effort. A mouse needs 3 to 4 grams of food a day. Crumbs fallen under the units, grains of rice that slipped under the plinth, the cat's kibble, grease on the extractor filters: that is enough. It has no need to open a cupboard at all, which explains why so many households inspect their food stores and find nothing.
A mouse does not settle where there is the most to eat: it settles where it is never seen, within three metres of a food source. A fitted kitchen ticks both boxes.
The five spaces nobody ever opens
The gap under the base units
This is the most important and the least understood. Kitchen carcases stand on adjustable legs; between the floor and the underside of the carcase there is a gap of 8 to 12 cm, continuous from one end of the run to the other, simply hidden by a clipped or screwed plinth. A mouse entering at one end can travel the full length of the kitchen without ever showing itself. What you typically find: droppings lined up along the walls, glass wool dragged out of a duct, shredded paper, and blackish greasy smears on the tiles.
The built-in oven housing
The oven slides into a housing wider than itself. The remaining space at the back and sides forms a warm corridor, and the supply cable almost always passes through an oversized cut-out in the back panel of the unit. This is one of the most consistent routes from the under-plinth void into the inside of the units.
The dishwasher and washing machine base
A dishwasher has no sealed underside: beneath the tub there is an open chassis, a drip tray and a motor. The water supply, the waste hose and the cable all pass through a single hole drilled in the partition of the adjoining unit — rarely sealed afterwards. This is where an active nest is most often found, because it offers warmth, humidity and total darkness.
The back of the fridge
The fridge is the only appliance that produces heat continuously. Behind the condenser grille, in the dust, a mouse finds permanent shelter at 25 °C. The signs are easy to read: droppings on top of the compressor, hairs stuck in the grease, sometimes cables with their sheathing gnawed.
The sink unit
Trap, hot and cold supplies, sometimes the main stopcock or the gas run: the back panel of the sink unit is the most heavily perforated wall in the house. It is also the most cluttered unit (cleaning products, bin, sponges), and therefore the least inspected at the back.
Inspecting in an hour, without dismantling the kitchen
Carry out the inspection in the evening if possible, with a torch, after turning off the room lights: grease marks and droppings show up far better in raking light.
1. Unclip a plinth. Modern kitchen plinths come away with a firm pull towards you at a clip; on screwed models, two cross-head screws are all there is. Start with the one closest to where you heard the noise, then the one on the sink unit. Run a torch along the void: you will see straight away whether there are droppings (3 to 6 mm, black, pointed at the ends for a mouse) or undisturbed dust.
2. Pull the fridge out. Unplug it, pull it out 30 cm, and shine a light on the rear grille and the floor. A vacuum with a crevice tool or a long technical brush will let you retrieve the debris: a mouse nest almost always contains paper, mineral wool and seeds.
3. Look under the dishwasher. Without pulling it out, remove the appliance's bottom panel (two screws on most models) and light up the chassis. Check the pipe penetration in the partition of the adjoining unit: if you can see daylight, a mouse can get through.
4. Open the sink unit and clear the base. Look for cut-outs around the trap and the flexible hoses, damp staining (a slow leak attracts rodents just as readily as woodlice) and droppings in the rear corners.
5. Lay down a detection marker. A thin dusting of flour or talc in two or three spots in the under-plinth void, over 20 cm, gives clear footprints in a single night. It is the most reliable way to know whether the run is still active before you block anything up. An infrared animal movement detector, placed facing the void for two nights, gives the same answer without the mess. A rechargeable LED head torch frees up both hands throughout this sequence, which makes all the difference when you are lying on the floor in front of a cabinet.
If you find droppings but they are dry, grey and crumbly, the occupation is old. Shiny, soft droppings and a strong smell of urine mean a current presence.
Sealing the runs: the right order of operations
The classic mistake is to seal up before dealing with the animals. If mice are inside the space when you close it off, they will look for another way out — often towards the living room — and you will end up with unreachable carcasses behind a cabinet.
The order that works:
- Remove the resource: thorough cleaning of the under-plinth void (vacuum, then degreaser), sensitive foodstuffs stored in rigid containers, cat bowl taken up at night.
- Trap inside the space for 7 to 10 days, until there are no new catches and no new marks on the talc at all.
- Seal up once the space is empty.
- Check at 15 days and at 1 month.
What holds, and what does not
| Opening | Durable solution | To avoid |
|---|
| Hole around a PVC pipe | Crumpled stainless steel wool + patching mortar | Polyurethane foam alone (gnawed through within a few nights) |
| Cable cut-out in a unit's back panel | Thin steel plate or perforated sheet, screwed on | Adhesive tape, cardboard |
| Gap under a kitchen plinth | Brush seal or low profile pressed to the floor | Silicone alone |
| Ventilation grille in a unit | Stainless steel mesh ≤ 6 mm | Plastic grille |
| Electrical conduit penetration | Clip + metal sleeve, sealed with mortar | Bare plaster |
An adult mouse gets through an opening of 6 to 7 mm — the thickness of a pencil. The practical rule: if a ballpoint pen fits, a mouse fits. And it will gnaw through any material softer than its incisors: plastic, softwood, expanding foam, plaster. Only steel, stainless steel, filled mortar and glass hold up over time. We covered these materials and how to use them in sealing rodent entry points.
For patching work inside a cabinet, two supplies are enough in most cases: a roll of stainless steel wool, which you crumple and pack into the opening, and a fast-setting patching mortar to lock it in place. As for tools, a smartphone inspection endoscope lets you look behind a dishwasher or inside an oven housing without dismantling anything, and saves you chasing false leads.
Trapping in a kitchen: the particular constraints
The kitchen is the room where chemical control is the most problematic and mechanical trapping the most effective, for three reasons: food is present, pets are present, and children may have access.
Snap traps or jaw traps should be set in the under-plinth void, perpendicular to the wall, trigger towards the wall — a mouse always runs along walls. Two to four traps for a standard-sized kitchen is the minimum: setting a single trap is the most common mistake. Bait with peanut butter or hazelnut spread, in very small amounts, and leave the traps unset for the first two nights to overcome wariness.
A live-capture mouse trap is an option, but it means releasing the animal more than a kilometre away and checking twice a day: in practice, few households keep that up. We compared the models and the setting method in trapping mice without poison.
Rodenticide baits in a kitchen: no. The use of anticoagulant rodenticides by private individuals is regulated, and ANSES regularly points out the risk of secondary poisoning for cats, dogs and wildlife, as well as the risk of accidental ingestion by a young child. In an enclosed space where food is present, bait placed behind a cabinet can also mean an unreachable dead rodent — and therefore flies and a smell for several weeks. The rules for private individuals are set out in what a private individual can really use.
Cleaning up afterwards: the part people rush
Rodent droppings are not merely unpleasant. Mouse urine and droppings can carry salmonella, and rats (brown rats) are the main carriers of leptospirosis in mainland France, as Santé publique France regularly points out. In a kitchen, contamination of worktops and crockery is the main risk.
A sensible protocol:
- Do not sweep dry or vacuum without precautions: that puts particles back into the air. Dampen the area first with a sprayer and detergent.
- Pick up with paper towel, into a sealed bag, and out to the outdoor bin.
- Then disinfect the surfaces: diluted bleach (one part 2.6% bleach to nine parts water) or a virucidal and bactericidal disinfectant compliant with EN 1276 / EN 14476, observing the stated contact time.
- Wear disposable gloves and, in an enclosed dusty space, an FFP2 mask: a disposable FFP2 mask costs a few euros and keeps you from inhaling dried droppings dust.
- Wash any kitchen textiles that have been in the affected space at 60 °C.
Throw away without hesitation any food in paper or cardboard packaging that has been sitting in a visited unit: a gnawed packet should be treated as contaminated.
When it becomes a job for a professional
DIY has clear limits in this context. Call in a professional if:
- the signs are present in several rooms and not just in the kitchen: the infestation is no longer localised and the entry point is elsewhere (cellar, loft, drainage);
- you find droppings larger than 10 mm: these are brown rats, not mice, and the source is very probably a buried network or a faulty connection — we described this in rats under the house;
- the runs are behind something you cannot safely remove (gas hob, built-in oven hard-wired in, ducted extractor hood);
- activity persists despite 10 days of proper trapping and removal of resources;
- you have gnawed cables: beyond the cost of replacement, that is an electrical risk and needs checking.
A professional brings three things a private individual does not have: identification of the species and its route, regulated access to products and secured bait stations, and a follow-up inspection. Indicative costs for a call-out are given on our pricing page, and the details of our rodent services on the services page. If you want to know whether your town is covered, the list is on service areas.
A protected kitchen: the year-round schedule
| Period | Action |
|---|
| Late October – November | Full inspection of the five spaces, talc markers laid down |
| November | Trapping if there is activity, cleaning and degreasing of the under-plinth void |
| December | Permanent sealing of pipe and cable penetrations |
| January – February | Monthly check of the under-plinth void, monitoring behind the fridge |
| Spring | Deep clean, check of plinth seals and grilles |
A properly sealed fitted kitchen is a highly effective barrier: most of the reinfestations described by Val-de-Marne professionals come down to a pipe penetration filled with foam, or a plinth that was never put back after an appliance repair. That is the kind of detail you can check in five minutes, once a year.
Unsure about what you have found behind your dishwasher, or facing activity that just will not stop? Describe the situation to us via the contact page; for a confirmed presence with bite marks, gnawed cables or a strong smell, go straight to emergency.
