Cleaning the waste stacks: the maintenance that prevents water damage

Backflow on the ground floor is never an isolated accident: it is the symptom of a stack nobody has cleaned in ten years.

Waste stacks run top to bottom through the building, collecting waste water from every flat. They silt up slowly: grease, scale, wipes, hair. Flow reduces without anyone noticing, until a flat at the bottom suffers backflow.

Preventive cleaning is one of the most profitable maintenance items a building has, and one of the most frequently absent from the budget. It costs a fraction of what a single water-damage claim really costs, excess included.

Signs of a stack clogging up

• Slow drainage reported by several flats on the same stack.
• Gurgling in traps when a neighbour runs water.
• Smells rising, particularly on the lower floors.
• Repeated one-off unblocking at the same point.
• Backflow on the ground floor or in the basement: the terminal stage.

The first signal is the most useful, and it is the one lost for want of a log: three isolated reports from three stacked flats form a diagnosis. See keeping an incident log.

What the contract covers — or not

Many buildings believe they are covered by a maintenance contract when they only pay for unblocking on demand. That is not the same: unblocking restores flow at one point, cleaning scours the inside of the stack.

• Is cleaning included, and how often?
• Which stacks are covered: waste, soil, rainwater?
• Does the contractor issue a report with points treated and anomalies found?
• Is a camera inspection planned where blockages recur?
• Are emergency call-outs included or billed separately?

The analysis is the same as for any recurring contract: see the cleaning contract specification.

What the board can easily obtain

Two simple requests to the manager change the picture: three years of intervention reports, and the total billed for one-off unblocking over the same period.

The second figure is often the decisive argument at a meeting: when emergency call-outs exceed the cost of annual preventive cleaning, the case is made. Same reasoning as in roof and waterproofing.

What is down to occupants

No cleaning compensates for usage: so-called biodegradable wipes, frying oil, food waste, cat litter. An annual, illustrated, blame-free information note noticeably reduces blockages.

It must reach every occupant, tenants included: see board communication. And a blockage that escalates becomes water damage.

Three emergency call-outs in a year cost more than preventive cleaning — and leave the stack in the same state.

Track your networks with CoproHarmony

CoproHarmony records each report with its flat and date, spots the stacks that keep coming back, and stores intervention reports. Create your free space.