How a soil stack is built
A soil stack runs vertically through the home or building. At the top it passes through the roof as a vent, so air can flow in and out. On each floor, branches come in from the fixtures. At the bottom, a bend makes the transition to the horizontal pipe under the floor, which runs to the outside wall and the external drainage. The rodding eye, a section with a removable cover, is usually just above the floor of the lowest storey.
In buildings from after about 1970, soil stacks are usually PVC. Older blocks often still have cast iron or sometimes asbestos cement pipes. Cast iron rusts on the inside and becomes rough, so debris catches more easily. Asbestos cement must not be drilled or sanded; the engineer then chooses an approach that spares the material and, if in doubt, recommends an asbestos survey by a certified firm first.
Why the lowest flat notices first
Water in a soil stack falls at speed and loses that momentum in the bend at the bottom. Any debris carried along stays there and in the start of the horizontal pipe. If that spot blocks, the water rises in the stack until it finds the lowest outlet. That is usually the shower or toilet of the lowest flat. The neighbours upstairs often notice nothing, which makes it all the more unpleasant for the residents downstairs. That is why a quick response matters.
Soil stacks in owners' association buildings
In an apartment building, the soil stack usually counts as a communal part and the owners' association (VvE) is responsible, but this depends on the deed of division. If in doubt, check the house rules or ask the managing agent. The branch from your own fixtures up to the soil stack is usually the resident's responsibility. We work for owners' associations, managing agents and landlords, both for urgent blockages and for periodic maintenance.
- Preventive jetting of all soil stacks in one round
- CCTV drain survey of older cast iron pipes
- Advice on repair or relining where cracks are found
- Clear agreements on access to the rodding eyes
- Explanation for residents about what does and does not belong in the drain
What residents can do themselves
A soil stack stays clear longest when all residents treat it with care. That starts in the kitchen: frying fat and cooking fat belong in a sealed jar in the general waste, not in the sink. In the bathroom a hair strainer in the shower drain helps, and only toilet paper belongs in the toilet. If you notice your drain gurgling or slowing down, report it straight away to the owners' association or landlord. An early report often means a small job, and a dry bathroom for the neighbours downstairs.