Rats in the Underground Car Park: Why They Move Into Cars in Autumn (and What Insurance Won't Cover)

The typical mid-October call doesn't come from an apartment. It comes from a garage mechanic — or rather from his customer: "They told me the wires in my car had been chewed through. €1,400 for the harness. The garage says it's rodents. But I've never seen a single rat in the building's car park." Two weeks later, a second owner in the same building calls about exactly the same thing. Then a third, who found scraps of insulating foam and hazelnut shells on the cabin air filter of his estate car.

Nobody has ever seen a rodent, and that makes perfect sense: an underground residential car park is the one shared space in a building where human activity drops to zero between 9 pm and 7 am — precisely the active hours of brown rats and house mice. The infestation isn't discreet by bad luck: it is invisible by design.

A vehicle parked for more than three days in an infested basement isn't an obstacle to a rodent: it's an ideal shelter. A warm engine bay, enclosed cavities, sound-insulation materials that are easily torn out for bedding, and cable sheathing whose hardness is perfectly suited to the continuous wear of incisors. In autumn, when outdoor temperatures drop and colonies look for winter shelter, the occupancy rate of stationary vehicles soars.

This article sets out how this autumn colonisation actually unfolds, the signs that let you spot it before the breakdown, the areas of a car park that feed the population, what insurance does — and above all does not — cover, and the technical protocol to insist on from your building manager before winter.

Woman inspecting her kitchen with a magnifying glass, standing near a table with fruit

Why October triggers the colonisation of vehicles

Three phenomena overlap across four to six weeks, and it is their simultaneity that makes the problem so serious.

The search for winter shelter. The brown rat (Rattus norvegicus) and the house mouse (Mus musculus) do not hibernate. They don't reduce their activity in winter: they relocate their nests inside buildings as soon as nights drop consistently below 10 °C, which in the Paris region corresponds to the second half of October. An underground car park holds a stable temperature of 12 to 16 °C all year round. It is the number one target in the neighbourhood.

Residual engine heat. A combustion engine stays warm for three to five hours after being switched off. For a rodent, that's a highly attractive thermal signal at the very moment it is scouting. Vehicles used daily are therefore visited, but rarely colonised: repeated starts disturb them. It's the low-use vehicles — the second-home car, the weekend car, the two-wheeler under a cover, the tradesperson's van parked every other week — that become permanent nests.

The scarcity of food outdoors. Surface resources (fallen fruit, terrace bins, seeds) disappear. Pressure concentrates on bin rooms, cellars and, by continuity, on the car park that almost always serves them.

What rodents are looking for in a car

Two behaviours need to be distinguished, and they are often confused.

Gnawing is not about food. A rodent's incisors grow continuously (roughly 10 to 14 cm a year in the brown rat): the animal has to wear them down mechanically. Flexible polymer cable sheathing is an ideal material for that. The old theory about "soy-based sheathing" used by certain manufacturers is regularly cited, but it doesn't explain the main point: pre-2010 vehicles with conventional PVC sheathing are just as badly affected as soon as the car park is infested.

The signs to look for before the breakdown

A chewed harness costs between €300 and €2,500 depending on the vehicle and the location. Yet the early signs appear two to six weeks before the electrical failure. Here they are, in order of frequency.

On the vehicle:

• A smell of urine or ammonia when the ventilation is switched on, especially in recirculation mode.
• Debris on the ground beneath the front bumper, directly below the engine bay: strands of grey foam, paper confetti, seeds.
• Paw prints and dark smears on the bonnet, on the windscreen near the wipers, or on the top of the tyres (rodents climb up via the tyre, then through the wheel arch).
• Intermittent warning lights with no mechanical logic: ABS, airbag, pressure sensor, a fleeting engine fault. A partially bitten harness creates intermittent contacts before the outright failure.
• Scratching noises on start-up.

In the car park:

• Black spindle-shaped droppings 15 to 20 mm long (brown rat) or black rice-grain droppings 4 to 6 mm long (mouse) along the walls, behind pillars, at the foot of soil stacks.
• Greasy blackish smears 5 to 10 cm wide along skirtings and conduits: these are the regular runways — rodents hug the walls.
• Gnawed bags of potting compost, storage boxes, child car seats stored in parking spaces.
• Holes 2 to 7 cm across at the foot of partitions, around pipe penetrations, in expansion joints.

A proper check is done with a torch held close along the walls: a powerful rechargeable torch reveals greasy smears and droppings far better than ceiling lighting, which is precisely designed not to illuminate corners. For a methodical owner, photographing every sign with the date is what will later make it possible to get the building manager to act.

Where the population comes from: the five entry points of a Paris-region basement

A car park is never colonised "by chance". In almost every case we diagnose in the Paris region, the origin lies among these five elements.

1. Direct continuity with the bin room. In most buildings built after 1970, the waste room is on the same level as the car park, or connected by a corridor. This is starting point number one: unlimited food, badly closing doors, non-sealed bins.
2. Service ducts and soil stacks. A rodent can climb vertically along a pipe 3 to 10 cm in diameter. Slab penetrations left unsealed after plumbing work are motorways between the basement and the upper floors.
3. Inspection chambers, floor gullies and sump pumps. A dried-out trap — common in car parks that are rarely washed down — becomes a direct connection to the sewer network. The brown rat swims and dives without difficulty.
4. The access ramp and the up-and-over door. A 2 cm gap under a metal shutter is enough for a mouse; 3 cm is enough for a young brown rat. The brush seals at the bottom of the door are almost always worn out.
5. Cellars and informal storage. Cardboard, furniture, bags of pet kibble, tyres, stockpiles of bottles: any cluttered storage unit is both shelter and larder. It's also the easiest factor to fix — and the hardest to get accepted at a residents' meeting.

Insurance and liability: who pays for the chewed harness

This is the most painful question, and the answer is surprising.

In motor insurance, damage caused by a rodent is not a covered event by default. It falls under neither collision, nor theft, nor glass breakage, nor storm. Some premium "fully comprehensive" policies include an "all-accident damage" cover which, depending on the wording, may include animal damage — with an excess, and it is not the norm. Many insurers explicitly exclude "damage caused by rodents, insects and animals". The only useful step: re-read the policy terms, search for the words "rodents" and "animals" in the list of exclusions, and request a written position before committing to the repair.

On the building-management side, the logic is different and more favourable. The car park is a common area. Maintenance of common areas and public-health standards are the responsibility of the owners' association, represented by the managing agent (French law of 10 July 1965). In rented housing, Article 6 of the law of 6 July 1989 requires the landlord to provide accommodation that "does not present any obvious risk to health" and is free of "pests and parasites", which extends to the outbuildings let with the property — including the parking space.

What tips a case one way or the other is never the amount of the quote: it's proof of prior notification. An owner who reported the presence of rodents to the managing agent in writing in September and suffers damage in November is in a radically different position from one who discovers the problem along with the garage bill.

Three practical habits:

• Report by email to the managing agent, with time-stamped photos and an explicit mention of the area (level -1, pillar B3, bin room).
• Request that the basement rodent-control contract be added to the agenda of the general meeting, by registered letter within the statutory deadlines.
• Keep garage quotes and reports that expressly name "rodents" as the cause — a report vaguely referring to a "damaged harness" is of no use.

The treatment protocol: what really works in a basement

A car park is a particular technical environment: large, ventilated, used by vehicles and sometimes by children and pets. Garden methods have no place there.

What a professional does

• Diagnosis before any treatment: mapping the runways, the nests, the water sources and the entry points. Without that map, bait is placed at random and the population simply redeploys.
• Secured, locked bait stations, fixed to the floor or to pillars, numbered and recorded in a logbook. Regulations on anticoagulant rodenticides (overseen by ANSES and the European Biocidal Products Regulation) require bait to be in boxes inaccessible to children and non-target animals, along with a limited treatment period and the removal of bait at the end of the campaign. A basement covered in loose bait for a year is an offence, not a protection.
• Mechanical trapping as a complement in sensitive areas (immediate vicinity of vehicles, bike room, inhabited cellars), to recover the carcasses and avoid the smell of decomposition inside a duct.
• Exclusion works: sealing slab penetrations with reinforced mortar or steel wool, stainless-steel grilles on traps and vents, brush seals at the bottom of doors, refilling floor-gully traps with water.

What an individual owner can do for their own vehicle

Without replacing collective treatment, a few measures clearly reduce the risk of a given car being colonised:

• Never leave food on board: crumbs under the seats, a bag of kibble in the boot, the packet of biscuits from the last trip. This is the single biggest factor in a rodent's choice between two neighbouring vehicles.
• Start and move the vehicle at least once a week, even for just 200 metres. Regular disturbance is often enough to discourage nesting.
• Open the bonnet once a month and inspect the cabin air filter area, the top of the battery and the scuttle tray. A simple rubber floor mat laid under the engine bay also makes nesting debris immediately visible on the ground.
• Use a repellent based on physical obstruction rather than smell: a grille or wire mesh over the engine bay's ventilation intakes, fitted by a professional, lasts far better over time than scented sachets. Ultrasonic car repellents are very hit-and-miss and lose their effect through habituation: they are no substitute for treating the car park.
• Keep the space clean: no cardboard, no stored tyres, no textiles. An airtight plastic storage box for workshop items or snow chains removes a potential nesting site from every parking space on its own.
• If you store bags of kibble or seed in the cellar, transfer them into a metal container with a lid. A plastic bag, however thick, is opened in a single night.

The mistakes that make things worse

• Putting loose rodenticide blocks in your parking space: a real risk for the building's dogs and cats, carcasses in inaccessible places, and no effect at all on the source colony.
• Treating only your own storage unit or vehicle when the source is the shared bin room: the population rebuilds in two to three weeks.
• Waiting for the annual general meeting in June to vote on a contract. With rodents, the useful window is September to November, before the colonies have established their winter nests and started breeding under cover. A female mouse can produce 5 to 10 litters a year; six weeks of delay isn't six weeks of nuisance, it's an extra generation.

Key takeaways

Damage to vehicles is the most expensive — and the latest — symptom of a basement infestation. By the time a harness has been chewed, the colony has been established for several weeks, and other vehicles in the same building will be affected in the months that follow.

The right sequence is the reverse of the one most buildings follow: torch inspection in October → written report to the managing agent → professional diagnosis of the basement and waste room → regulated treatment + exclusion works, rather than "breakdown → garage quote → insurance battle → vote at the general meeting the following year". A rodent-control contract covering the common areas of a Paris-region building costs, at the scale of an owners' association, a fraction of a single replaced wiring harness.

If you notice droppings along the pillars, greasy smears on the skirtings or foam debris under a bumper, have a full basement diagnosis carried out — bin room, cellars, ducts and car park — before winter. Our teams work with residential buildings and businesses across the Paris region, providing a treatment logbook and a recommendations report you can use at your general meeting.