Bed bugs throughout the building: the treatment plan

There is a precise moment when a bed bug case stops being an apartment problem and becomes a building problem. That moment is not the first report. It's the third — usually on the same staircase, often on neighbouring or stacked floors, and almost always several weeks apart, because the first two occupants said nothing for months.

At that stage, a manager's usual reflex is to order a treatment for the unit that has just complained. That is precisely the decision that drags the case out for two years. A bed bug (Cimex lectularius) does not stay in the apartment where it was born: it travels through service ducts, skirting boards, slab penetrations, refuse chutes and, above all, through the occupants themselves and their belongings. Treating one unit in the middle of an infested staircase is like repainting one cabin on a boat that's taking on water.

This article describes how a building-wide treatment is actually put together in the Paris region: who decides, in what order units are inspected, which schedule holds up, and what happens when an occupant refuses access.

Brick façade of an older multi-storey apartment building under a blue sky

When should you treat the building rather than the apartment?

The three-household threshold

In our experience with social landlords and apartment blocks across the Paris region, the switch is decided on three criteria, not just one:

• Several reported units on the same staircase (from two confirmed cases, three if you count unverified suspicions).
• Vertical or horizontal adjacency: stacked units, units sharing a party wall, or units served by the same landing duct.
• Re-infestations after a properly conducted treatment in a unit: if a flat treated by the book tests positive again within three months, the source lies outside that unit.

A fourth signal, often overlooked: bed bugs found in common areas — staircase, bike store, caretaker's lodge, lift, shared laundry room. They don't breed there for long, but their presence is proof of active movement between units.

What is not a criterion

How badly an occupant says they are affected tells you nothing about how far the infestation has spread through the building. A heavily infested unit can be an isolated case; three lightly infested units in the same column make it a collective case. Likewise, cleanliness is irrelevant: the bed bug is not a hygiene pest, it feeds exclusively on blood. A spotless three-room flat belonging to an executive in Boulogne and a cluttered unit in Goussainville pose the same technical problem — the second simply takes longer to prepare.

Step 1: systematic inspection, unit by unit

This is the step managers always want to skip for cost reasons, and it's the one that determines whether everything else succeeds.

The scope to inspect

The principle is simple: every unit in physical contact with a positive unit gets inspected. In practice, for a reported apartment on the third floor left, that means third-floor-left's upstairs and downstairs neighbours, the right-hand and middle flats on the same floor, plus any unit connected to the same service duct. On a staircase of 10 to 15 units with three reported cases, you very quickly reach the entire staircase — and that is often the economically sound decision, because a second round of inspections six weeks later costs more than one complete inspection up front.

What a technician is really looking for

Visual inspection focuses on signs, not live insects (which you almost never see during the day):

In building-wide cases, visual inspection is backed up by passive detectors placed under the bed legs (interceptors), checked at 7 and 15 days: they provide objective evidence of presence in doubtful units and, above all, in those where occupants deny everything. For units reported negative but sharing a wall with a positive one, the manager has every reason to leave bed bug interceptors in place for the duration of the campaign: it's the only way to know whether the staircase is becoming re-contaminated along the way.

Canine detection, carried out by certified teams, has its place on very large cases (developments of more than 60 units) to quickly sort out which units need treating. It never replaces visual confirmation before treatment.

The inspection record, part of the case file

Every unit inspected must have a dated record stating: the unit, whether the occupant was present, the result (positive / negative / doubtful), the level of infestation, the rooms concerned, and the preparation required. These records make up the landlord's or managing agent's file. In the event of a tenancy dispute — and they do happen, particularly around housing fitness standards and the departmental public health regulations — this is what demonstrates that the manager acted, when, and over what scope.

Step 2: the schedule, and why it isn't negotiable

The principle of simultaneous treatment

The technical rule is this: all positive and doubtful units on the same staircase must be treated within the same time window, ideally across two to four consecutive days. As soon as you spread the visits over three weeks, bed bugs from the as-yet-untreated units recolonise the ones just treated. This is the number one reason campaigns drag on forever.

A realistic visit schedule

Two visits are a technical minimum, not a commercial option: bed bug eggs are barely affected by the products and hatch within one to two weeks. A quote that provides for only one visit to a building should be ruled out — we set this out in detail in our article on what an intervention really costs and what a quote should contain.

Steam, heat, chemicals: what works in combination

In a building, the choice is never binary. In practice:

• Dry steam above 120 °C treats bedding, textiles, seams and skirting boards with no residue. Essential in children's bedrooms and in homes with vulnerable people.
• Professional insecticides (pyrethroids combined with a growth regulator, or alternative active substances) provide residual action on movement routes. Be aware: ANSES has repeatedly highlighted the growing resistance of bed bug populations to pyrethroids used alone, and has warned about unauthorised products in circulation; we return to this in the alert on banned insecticides.
• Whole-unit heat treatment (raising the temperature to 50-55 °C for several hours) resolves a heavily infested unit in a single visit, but requires removing heat-sensitive items and costs considerably more. It is reserved for severe cases, not for an entire staircase.

Step 3: preparing the units — what occupants must do

A building-wide treatment also fails through poor preparation. Instructions must be written, illustrated and distributed ten days in advance, not the night before:

• Wash all laundry and bedding at 60 °C, or failing that run it through the tumble dryer for 1 hour on a high setting, then store it in sealed bags until the end of the campaign. Large-capacity sealable zip plastic bags prevent clean laundry from being re-contaminated between the two visits.
• Dismantle the bed if possible, pull furniture 20 cm away from the walls, empty bedside tables.
• Take nothing out of the unit: a mattress carried down to the courtyard or a sofa left on the landing contaminates the whole staircase. If an item has to be disposed of, it is wrapped, slashed and removed through the waste channel.
• Do not use consumer insecticide sprays before the visit: they scatter the bugs towards neighbouring units and make treatment harder. Repellents, diatomaceous earth and other comfort solutions have no proven effectiveness against an established infestation.
• Plan to be able to stay out of the unit for the ventilation period specified by the technician.

After the campaign, keeping anti-bed bug mattress encasements in place (full zip-up encasements, kept for at least a year) is the only durable protective equipment that genuinely benefits occupants. In furnished units and developments with high turnover, a powerful focused-beam torch kept in the caretaker's room makes it possible to run quick checks between contractor visits.

Step 4: refused access, the real sticking point

This is the question landlords and managing agents always ask us: what do you do when an occupant refuses to let the contractor in?

One refusal is enough to sink the campaign

It needs to be said plainly to residents' committees and letting management teams: a single untreated unit on an infested staircase wipes out much of the campaign's benefit. The money has been spent, the occupants have washed everything, and the re-infestation starts again from the unit that stayed shut.

The escalation to follow

1. Human contact first. In the vast majority of cases, refusal is not bad faith: it's shame, fear of being judged, worry that a cluttered home will be reported, or a physical inability to prepare the unit. A visit from the caretaker or the manager resolves a large share of refusals.
2. A registered letter, setting out the tenant's obligation to allow access for works necessary to the upkeep and preservation of the property, proposing a new date and stating the consequences of continued refusal.
3. A formal notice, then an application to the protection litigation judge for an access authorisation. It's slow, but it's the only lawful route: no landlord, managing agent or contractor can force entry into an occupied home.
4. Help with preparation. For elderly, isolated occupants or those living in squalor, the right answer is often a clearance and preparation service, paid for by the landlord and combined with the treatment. It costs less than running the whole campaign again.

For apartment blocks, the case is complicated by a point that needs anticipating: a managing agent cannot commit expenditure on this scale on privately owned areas without a mandate. In practice, the general meeting vote covers the common areas plus a negotiated framework service that each owner or tenant signs up to for their own lot. This is an arrangement that needs preparing, with several quotes attached to the meeting notice; our page dedicated to services for managing agents and residents' committees explains the mechanics, and the building hub sets out the collective services available.

Who pays for what: the emerging lines

No single rule covers every situation, but practice in the Paris region and recent case law point to some benchmarks:

• In rented housing, the landlord must provide a home that is fit to live in and free of pests; since the 2023 bed bug law, the presence of bed bugs explicitly falls within the scope of housing fitness. In practice, the landlord covers the treatment, unless they can show that the introduction is attributable to the occupant — rarely an easy thing to prove in a building with multiple affected households.
• In an apartment block, treating the common areas and ducts falls under common charges; treating individual lots remains a private matter, unless the general meeting decides otherwise.
• In social housing, most landlords in the Paris region have incorporated bed bug control into their maintenance contracts, with scheduled campaigns. The friction point is no longer payment but turnaround time.
• Ancillary costs (clearance, replacing bedding, temporary accommodation) almost never appear in the treatment quote. They have to be budgeted separately. How they are shared out ties in with the issues we cover in the check-out inventory and pests.

After the campaign: monitoring, not forgetting

A cleared building remains an exposed building, especially in the Paris region where tenant turnover is high. Three measures stand the test of time:

• A single point of contact (caretaker, manager, member of the residents' committee) to whom every report is sent, with a notice posted in the lobby: reporting early costs nothing, reporting late costs a whole campaign.
• Interceptors left in place in previously positive units for six months, checked monthly.
• A move-in protocol: systematic inspection at every re-letting on the staircases concerned, and written information for new occupants. For furnished units and short-term lets, we set out the protocol to apply between occupants in this article on holiday rentals.

Finally, a word about pace. A serious building-wide campaign runs over six to ten weeks from the initial inspection to the final check. Contractors who promise a cleared building in ten days are ignoring the insect's biological cycle. Those who let a case drag on for a year have failed to organise simultaneous visits. In between, there's a schedule, inspection records, two to three interventions per unit, and a manager chasing up the absentees — nothing more sophisticated than that, but nothing less either.

If your staircase has reached its third report, the right time to request a full inspection and a quote for collective treatment was six weeks ago. The second-best time is today.