Can Cockroaches Spread Between Flats?

How They Move

Service risers, which run vertically through the building and connect every flat on the stack. Ducting and extract runs. The voids around soil pipes where they pass through floors. Wall cavities. Under floors. And communal areas — corridors, bin stores, refuse chutes and plant rooms.

None of that requires them to cross a corridor or go outside. A cockroach can move between flats without ever entering a space anyone can see.

Why One Flat Treated Alone Often Fails

If the neighbouring flat, the flat above or the bin store is producing cockroaches, treating yours removes the ones in it and leaves the supply intact. Numbers fall, then recover.

That is why the honest answer to "will one treatment fix it" in a block is sometimes no, and why we say so before taking the booking rather than after the second visit.

How to Tell Whether It Is Your Flat or the Building

Where the activity concentrates is the clue. Cockroaches appearing first and most around the boxing for the soil stack, the riser cupboard, the extract vent or the front door threshold points outward. Activity concentrated around your own fridge and units points inward.

Ask neighbours. It feels awkward and it is the single most useful thing you can do, because people in blocks routinely assume they are the only one and stay quiet about it.

What to Ask the Managing Agent For

A block-wide inspection rather than flat-by-flat treatment. Attention to the communal parts — bin store, chute, risers and plant rooms. And sealing of the service penetrations between flats, which is usually the cheapest single intervention available.

Put it in writing and be specific. "There are cockroaches" gets a contractor sent to one flat. "Activity is concentrated at the riser cupboard and the soil stack boxing, which suggests movement between flats through the service voids" gets a different response.

What Is Worth Doing in Your Own Flat Meanwhile

Seal what you can: the gap around the soil pipe boxing, the waste pipes under the sink, the gap at the extract vent, and the threshold under the front door. That reduces traffic in even when the building is untreated.

And have the flat treated — £190 — with monitors left, because monitors are what prove to a managing agent that activity is continuing and where it is coming from. A written report is worth more in that conversation than a complaint.