Rats in the Bin Room: Reading a Building's Yard

When a caretaker calls us about "rats in the yard", we never start by putting out bait stations. We start by walking slowly along the walls, torch held low, looking at the ground and the corners. In twenty minutes, a building's yard tells the whole story: how long the rats have been there, where they get in, what they eat and roughly how many there are.

The brown rat (Rattus norvegicus) is the species found in 95% of yards and bin rooms across the Paris region. It burrows, it is neophobic, it is a creature of habit. Those three traits explain both the signs it leaves behind and the mistakes made by buildings that try to deal with it on their own.

The yard before the bin room: reading the runways

A brown rat does not cross open ground. It hugs the edges. It always takes the same route between its burrow and its food source, and that route follows a wall, a kerb, a pipe, the base of a hedge. This repeated path is called a runway.

On paved or concrete ground, a runway shows up as a band 4 to 7 cm wide, slightly cleaner or more polished than the surrounding surface, sometimes swept free of dust. On soil or gravel, it is a packed-down trail. At the foot of a wall overgrown with ivy or box, it is a tunnel of flattened vegetation at ankle height.

Runways answer the first useful question: where does the population travel. A bait station placed three metres from a runway, in the middle of the yard, will never be visited. Placed on the runway, against the wall, it is inspected on the very first night.

Grease marks and gnaw marks

Wherever a runway passes through a tight spot — the bottom of the bin room door, a hole in a low wall, a gap under a grating — the rat's coat leaves behind a mix of sebum and dust. This forms a dark brown mark, smooth to the touch, that builds up over months. These rub marks are the best indicator of how long the problem has been running: a clear, black mark means daily traffic over a long period, not a one-off visit.

On joinery, look for gnawing. The brown rat chews soft wood, PVC, door seals and electrical conduit. Fresh marks are pale, almost yellow, and the shavings on the floor are still crisp; an old mark is greyed and dusty.

Burrows, the sign that changes everything

This is the detail most often missed by residents' committees. The brown rat digs. In a building's yard, it settles:

• under loose slabs and paving stones that move underfoot;
• in planters and soil beds, especially against a wall;
• at the foot of hedges and under compost bins;
• in backfill along party walls, and in poorly sealed wastewater inspection chambers.

An active burrow entrance is 6 to 9 cm across, with clean, smooth edges, packed earth in front of it and no spider's web across the opening. An abandoned burrow fills with leaves and debris. Counting active entrances gives a far more reliable order of magnitude for the colony than counting the animals seen in daylight — because seeing rats in broad daylight already signals a dense population and competition for food.

Close-up of a brown and white ferret looking at the camera, sitting on a wooden board

The bin room: the five points we check

The bin store is the canteen. In a building with 30 units, it concentrates enough organic matter each week to feed several dozen rodents. Here is the checklist we apply every time.

1. The bottom of the door. A rat gets through a 2 cm gap, and enlarges a smaller one by gnawing. Bare wooden door bottoms are almost always chewed. A flat threshold with a fabric draught excluder is useless: you need a metal kick plate or a screwed-on stainless steel door strip.

2. Conduits and penetrations. Every pipe, cable or extractor passing through the bin room wall is a potential entry point. We look for unsealed openings, split sleeves, crumbling mortar around a wastewater downpipe.

3. The containers themselves. Broken lids or lids propped open, bins holed at the bottom, bags left beside a bin because it is full: in every case, food is available all night long.

4. The floor and the floor drains. A sloped floor with a working floor drain can be washed down. A dry or broken trap becomes a direct route into the sewer network — and that is where the rats come up.

5. The droppings. Brown rat droppings are 15 to 20 mm long, shaped like a thickened grain of rice, often in clusters. Mouse droppings are 3 to 6 mm. The distinction changes the protocol, the entry points and the type of stations. We covered it in detail in our article on what rodent droppings reveal.

Field rule: if the bin room is not closed, washed and sealed, no amount of baiting will bring the population down for good. The rats you remove are replaced by those from neighbouring plots within a few weeks.

Why DIY attempts fail

Every autumn, we are called into buildings where the residents' committee has bought blocks of rat poison from a supermarket and scattered them around the yard. Three problems, always the same ones.

Neophobia. The brown rat is wary of anything new in its environment. A block left out in the open in the middle of a run is avoided for days, sometimes for good. It has to be protected, placed on a runway and left undisturbed.

Unprotected bait. Since the European rulings governing anticoagulants, professional rodenticides must be used in secured stations that are inaccessible to other animals. A loose block in a yard where cats and birds come and go is a secondary poisoning risk, not a method. Anses, the French agency that assesses these active substances, stresses that their use must remain controlled, time-limited and combined with non-chemical measures.

Stale or out-competed bait. Bait that stays untouched for two weeks does not mean there are no rats left: it means the bins are tastier. As long as the food source stays open, the bait loses the comparison every time.

One last common mistake: blocking a hole and doing nothing else. If the population is already established inside, sealing it up pushes the rats towards the service ducts, the rubbish chutes and the cellars — in other words, towards the flats. The order matters.

The Méthode Verrou applied to a building's yard

We work in a fixed sequence: detect, exclude, treat, monitor.

Detect

A full survey of the yard, the bin room, the cellars, the inspection chambers and the plant rooms. Mapping of runways, active burrows, grease marks and entry points. Placement of monitors — tracking dust or non-toxic blocks — to measure the actual pressure before any treatment. This is the phase that sizes the job and avoids billing for ten stations where three well-placed ones will do.

Exclude

This is the building fabric and hygiene side, and it is the part that belongs to the co-ownership. Sealing penetrations with mortar reinforced with stainless steel mesh or with steel wool — expanding foam on its own is chewed through in a single night. Fitting a metal strip at the bottom of the door. Restoring floor drains. Rodent-proof grilles on air inlets. For inspection chambers and wall penetrations, galvanised wire mesh on a roll does the job very well, provided it is sealed in place rather than simply laid over the opening.

On the waste side: set times for putting bins out, repaired lids, a ban on bags left on the floor, weekly cleaning of the room with a hose and degreaser. A caretaker equipped with a good pressure washer can deal in twenty minutes with a floor that would otherwise stay greasy all year.

Treat

Secured, labelled bait stations placed on the runways and at burrow entrances, with a logbook: plan, installation date, consumption recorded at each visit. In enclosed yards, we prefer mechanical trapping in locked boxes when pets are around. Details of our interventions are on our rodent extermination page and the price list on the pricing page.

Monitor

Two or three visits in quick succession, then regular follow-up. A yard in the city centre is never "permanently" cleared: it is kept under control. That is exactly what an annual prevention contract covers, with consumption records and traceability you can present at the general meeting.

Beige and brown ferret walking against a plain black studio background

Who decides, who pays, who does what

The yard, the bin room, the cellars, the service ducts and the vertical pipework are common parts. The rats moving through them are therefore the managing agent's responsibility, not the occupants'.

In practice, a written report to the managing agent — dated email, photos of the droppings and runways, locations — triggers an intervention far faster than a verbal remark to the caretaker. The Code de la santé publique (French Public Health Code) requires the owner to provide housing free of pests, and the Paris departmental sanitary regulations govern the upkeep of waste storage rooms. When several units are affected, the right vehicle is a plan voted at the general meeting, as we explain in our article on voting through a pest control plan in a co-ownership. For collective decisions and quotes to present to the residents' committee, our managing agents page sets out the framework for our work.

One point that is often overlooked: road works, building sites next door and sewer cleaning all displace populations. A yard that has been quiet for three years can be colonised in a fortnight because a neighbouring building has been treated or a pipe has been opened up. That is not a failure of the follow-up, it is outside pressure — and it is why sealed entry points remain the best insurance.

What a caretaker or committee member can record alone

No treatment, but a useful survey that saves an entire visit:

1. Walk round the yard at dusk, torch held low, following the walls: note the runways and the burrows. A wide-beam torch shows grease marks far better than a phone.
2. Photograph the droppings with a reference object beside them (a coin) to settle whether it is rat or mouse.
3. List every unsealed opening in the bin room and the cellars, including its height above the floor.
4. Check the floor drains and inspection chambers: smell, grating, seal.
5. Note the times the bins are put out and the condition of the lids over the course of a week.
6. Set a motion-activated trail camera in a cellar corridor: in two nights it reveals the exact times and routes, without disturbing the population.

With that survey in hand, the technician arrives with a station layout almost written already, and the co-ownership knows which works to price up. If the situation is further along — rats visible in daylight, activity in the living areas, a smell of urine in a cellar — start from our emergency page, and an on-site survey can be scheduled through online booking.

FAQ

How long does it take to bring a rat population in a yard down?

With an established infestation, allow four to eight weeks to see bait consumption collapse and fresh signs disappear, provided the sealing works and the bin room hygiene are tackled in parallel. Without those two strands, the drop is only a temporary dip: the burrows are recolonised from neighbouring plots as soon as treatment pressure eases.

Can the managing agent refuse to act, claiming the problem comes from a flat?

They can argue that, but the evidence settles it quickly. Runways and burrows in the yard, grease marks at the bottom of the bin room door and droppings in the cellars all point to the common parts, and therefore to collective responsibility. A written report with photos, repeated and sent to the managing agent with a copy to the residents' committee, builds the file needed to obtain a survey and then a quote to put before the general meeting.

Should bait be put out in the yard when there are cats and dogs around?

Rodenticides may only be used in locked, fixed and labelled secured stations, precisely to keep pets out and avoid the risk of secondary poisoning. In a busy yard, we often favour mechanical trapping in closed boxes and shift most of the effort onto sealing entry points and managing waste, neither of which poses any risk to animals.