Service Shafts: The Rat Highway in Apartment Blocks

The contractor has been on site six times in eight months. Bait stations in the basement, the courtyard-side air vent sealed, a new grate on the bin room floor drain: the technical file is impeccable, and bait consumption in the cellar has indeed dropped. Yet in October, three reports come in from the fourth floor of stairwell C — scratching noises behind the bathroom boxing, a bag of rice torn open in an under-sink cupboard, droppings on a kitchen skirting board. The residents' committee concludes that "the treatment isn't working".

It is working perfectly well. It is simply treating the wrong plane. In a multi-unit building, rodents do not move only horizontally at basement level: they climb, floor by floor, inside the vertical service shafts that run through the building from cellar to roof. Wastewater stacks, landing distribution shafts, heating ducts, electrical conduits, the crawl space beneath the slab: this network is continuous, heated, dark, never cleaned and almost never inspected. It is the single most rodent-friendly piece of infrastructure in the entire Paris-region housing stock, and it appears in no standard quotation.

This article describes how to identify these vertical routes, how to read incident reports back to the stack involved, which repairs fall to the common parts or to the private units, and in what order to commission them so that pest control stops being an endless subscription.

Empty apartment room with carpet, skirting boards and an archway leading to a tiled hallway

Why a building is a vertical network before it is a set of flats

The brown rat climbs, the mouse goes everywhere

Two misconceptions circulate at general meetings. The first: "rats stay in the basement". The brown rat (Rattus norvegicus), the dominant species in the Paris region, is an excellent climber as soon as it has something to grip — a cast-iron pipe, a rough conduit, a corner of masonry. It will happily climb two to five floors inside a service stack, especially when the outside temperature drops and the shaft becomes the most temperate volume in the building.

The second: "there isn't enough space". A house mouse gets through an opening of 6 to 7 mm, a young brown rat through 20 mm. Inside a shaft, gaps of that size number in the dozens: play between conduit and partition, the hole where a gas hose passes through, an abandoned drilling left after a stack was replaced, a slab joint left open at every floor penetration.

The five vertical routes to know

What they have in common: none of these routes has an operational owner. The plumber works on his stack, the telecom operator on his conduit, the heating engineer on his duct — and each leaves behind the hole he made. After twenty years of successive connections, the building is perforated vertically over its entire height.

Reading the reports to find the stack

The alignment rule

A log of reports sorted by building is useless. It has to be sorted by stairwell, by stack and by room. The useful question is not "how many flats are reporting?" but "are the reporting flats stacked one above the other?".

• Reports on the 2nd, 3rd and 5th floors of the same stairwell, all in kitchens or bathrooms → a wastewater stack or vertical service shaft is involved.
• Reports scattered across a single level, in all orientations → horizontal movement (ground-floor slab, crawl space, retail unit's suspended ceiling).
• Reports concentrated on the first two levels → movement up from the basement or the sewer network.

This reading is done on a six-column table: date, stairwell, floor, flat, room, evidence found (noise, droppings, damage, smell). It is exactly the document a serious contractor asks for before pricing, and the one whose absence explains most contracts that go round in circles. The structure of this log matches the one described in our article on the pest control register.

Shaft inspection in practice

Inspecting a stack takes twenty to forty minutes per stairwell and requires no demolition:

1. Open the service cupboards on every landing and look at the floor of the shaft: droppings fall and accumulate at the bottom of each level.
2. Light the shaft upwards and downwards. A powerful rechargeable LED torch beats a phone light: you are looking for greasy rub marks on the pipework, the signature of repeated passage.
3. Locate the drillings: note the floor, the approximate diameter, the type (conduit, flexible hose, cable).
4. Place indicators: a patch of flour or a tray of inert tracking dust at the bottom of the shaft reveals within 48 hours whether the route is active. A movement detector or a non-lethal witness trap usefully completes the survey in accessible shafts.
5. Check the stack base in the basement: that is where, in 70% of the cases we see, the real entry point lies — an inspection chamber with no cover, a cracked soil pipe, a dried-out floor gully.

A dried-out floor gully deserves a special mention. In a cellar or a little-used service room, the water seal evaporates within a few weeks and the gully becomes an open door onto the wastewater network. Filling it with water does not last three weeks; what is needed is a screwed-down grate or a non-return valve.

Brown mouse climbing a wooden fence, surrounded by green foliage

Who decides, who pays: the real split

Common parts, private parts

In the vast majority of co-ownership rules, the vertical network is a common part: soil stacks, general pipework, service shafts and penetrations through the floor slabs. Individual connections inside the flat, by contrast, are private. The practical consequence is simple:

• Sealing a landing penetration, repairing a stack base, fitting a grate over a cellar floor gully: collective decision and funding, common charges.
• Sealing the hole under a sink, behind a washing machine or around a gas hose inside the flat: at the occupant's or the landlord's expense, depending on the tenancy agreement.

In the rental sector, the call is made with reference to the decree on the characteristics of decent housing and the departmental public health regulations, which require the landlord to provide housing free of infestation and protected against water ingress and pests. A tenant facing an active stack does not have to fund the structural repair; they must, however, report it in writing and grant access.

What the managing agent can commission without waiting for the general meeting

The managing agent has two immediate levers. First, emergency protective works needed to safeguard the building, which can be carried out without prior authorisation from the general meeting. A collapsed stack base or an inspection chamber with no cover fall into this category. Second, performance of the existing maintenance contract: a shaft inspection requested from the contractor under contract requires no vote if it falls within the scheduled visits.

What does require a vote, by contrast: a sealing programme across all landings, replacement of a stack, the fitting of new shaft doors. These amounts are prepared at the same time as the annual contract — the method for putting them to the vote is detailed in our guide to getting a pest control contract approved at the general meeting.

In the Paris region, the departmental public health regulations restate the obligation on owners and occupants to keep premises free of rodents and to carry out the necessary rodent control operations. Passage through a shaft exonerates no one: it simply identifies who is responsible for the section concerned.

Cutting the routes: the order of works that works

1. The stack base and the basement, always first

Sealing a landing on the 4th floor while the stack base remains open in the cellar just moves the problem up one level. The order is not negotiable: you close off access to the network, then close off access to the fabric of the building, then deal with the residual population.

The right materials are well known and inexpensive: patching mortar for drillings in masonry, fine-mesh stainless steel mesh for openings that must stay ventilated, sealing collars around conduits, stainless steel wool to caulk narrow gaps. Polyurethane foam on its own does not hold: a brown rat goes through it in one night. It is only worth using behind a mesh backing. The full method is described in our article on sealing rodent entry points in a building.

2. The landings, from the bottom up

You then work up stairwell by stairwell. Each service cupboard gets: a door that actually closes (a lock or catch, not a tired magnet), a clear floor — landing shafts are often used to store cardboard and cleaning products — and the penetrations sealed around the pipework. Simply cleaning out the shaft already changes the diagnosis: on a bare floor, any new dropping is visible at the next visit.

3. The flats, as a grouped campaign

Private drillings under sinks and behind appliances must be dealt with within the same time window, otherwise the stack stays supplied. That means an information campaign and an access schedule — with the classic difficulty of absent or reluctant occupants, covered in our article on the tenant who refuses access for treatment.

For occupants, two useful and achievable steps: store dry goods in airtight food containers rather than in an open bag in a low cupboard, and fit a draught excluder to the bottom of the entrance door, which often leaves a 10 to 15 mm gap opening straight onto the landing and its shaft.

4. Treatment, last

Once the routes are cut, chemical or mechanical control becomes effective because it applies to a closed population. It must comply with the rules on securing baits in common parts, particularly in buildings with children and pets: stations locked, fixed, numbered and logged. These requirements are set out in our article on rodenticide baits in apartment blocks.

Empty apartment room with white walls, wooden skirting boards, laminate flooring and a window

What to insist on in the quotation

A "building rodent control" quotation that lists only basement bait stations does not answer a vertical problem. The line items to demand:

• Inspection of the landing service shafts: number of stairwells, number of levels visited, expected deliverable (annotated plan, photos by floor).
• Location of the stack bases and condition observed, with dated photographs.
• Survey of drillings by floor and by type, priced separately from the sealing work.
• Placement of activity indicators and the date they will be read (48 to 72 hours).
• A clear distinction between what falls under the maintenance contract and what constitutes building compliance works.

Without that distinction, the co-ownership pays for years for maintenance that compensates for a building defect instead of correcting it. That is the difference between a stable pest control budget and one that drifts. The criteria for comparing contractors on this point are developed in our analysis of rodent control tenders, and the technical framing in the specification for a pest control service.

The case of the crawl space

One last forgotten volume: the crawl space beneath the slab, common in Paris-region buildings from the 1930s to the 1970s and in buildings with ground-floor retail units. It is continuous across the whole footprint of the building, inaccessible without a hatch, and forms a population reservoir that nothing reaches. Inspecting it is a specific service, sometimes using an inspection camera, and it determines the success of everything else when reports cluster on the ground and first floors. Commercial premises with a suspended ceiling or a basement stockroom raise the same kind of boundary question, dealt with in our article on rodents in a ground-floor retail unit.

Key takeaways

• Reports on the upper floors do not mean a treatment is failing: they indicate an active vertical route.
• Sorting reports by stairwell, stack and room is the most cost-effective diagnostic step there is, and it costs nothing.
• The vertical network is a common part; drillings inside a flat are not. That boundary determines who pays.
• The order of works is stack base → landings → flats → treatment. Reversed, it guarantees a recurrence.
• A credible quotation prices the shaft inspection separately from baiting and distinguishes maintenance from compliance works.

For a building, a residential estate or a rental portfolio in the Paris region where reports are moving up through the floors despite an ongoing contract, a targeted stack inspection is the starting point. You can request a quote or look at our dedicated offer for buildings and co-ownerships and for managing agents and property managers.

Sources and references: Anses (assessment of rodenticide products and uses in inhabited environments); INRS (biological risks linked to rodents and work in confined spaces); Santé publique France (rodent-borne zoonoses, including leptospirosis); departmental public health regulations of the Paris region; decree no. 2002-120 on the characteristics of decent housing; law no. 65-557 of 10 July 1965 establishing the status of co-ownership of built property.