Soil stacks are the installation nobody thinks about until a stain appears on the ceiling of the flat below. They are vertical pipes running the full height of the building, buried in walls or service ducts, and in many blocks in this province they have been working for over fifty years without anyone ever looking at them.
At Grupo Construcciones Alicante we replace and repair soil and rainwater stacks in buildings across Alicante and the province. We work mainly with residents’ associations: we locate the point of the leak, assess whether a local repair or replacing the whole stack makes more sense, and carry out the work coordinating access to the affected flats, which is usually the trickiest part of the job.
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Replacing an old stack avoids the most expensive problem a residents’ association can have: a continuous leak. Waste water escaping from a failed joint doesn’t stay in the service duct; it soaks the wall, appears in the kitchen or bathroom of several flats and ends in arguments about who pays what, with insurance claims and works inside other people’s homes.
And there is one improvement that surprises everyone: the noise. Old cast-iron or plain PVC stacks transmit the sound of every flush right up the column. Replacing them with acoustic pipework and resilient brackets removes that background noise many residents had assumed was unavoidable.
Replacing a stack affects a whole building, so we do it in this order:
We locate where the leak actually comes from, which is rarely where the stain appears. Where necessary, we survey the inside of the stack with a camera before deciding anything.
A fixed quote with the metres of stack, the material, the access hatches planned and the building and decorating work needed to leave the affected flats as they were.
We agree the access days with the managing agent and each resident, and protect the communal routes before anything is opened up.
We open up the duct or the pipe run, replace the stack section by section with correct falls, and fit resilient brackets and expansion couplings.
We test the stack with water from the upper floors, checking the joints and confirming there are no leaks before closing anything up.
We close up, fit the access hatches, make good tiling and paintwork in the opened areas and hand over the tested stack with a written guarantee for the association.
Foul and rainwater. Soil stacks carry waste from bathrooms and kitchens; rainwater downpipes take the water from roofs and terraces. They should not be mixed where the building has a separate system, and it is worth checking that no terrace is discharging into the foul system, something that turns up frequently in old refurbishments and causes smells.
Materials. In older buildings it is common to find cast iron, salt-glazed clay or asbestos cement. Today the replacement is PVC drainage pipe or, better still, multilayer polypropylene acoustic pipe, which greatly reduces flush noise. The material matters less than the workmanship: correct falls, properly made joints and brackets that allow for expansion.
Venting the system. A stack needs venting so that discharges do not siphon the traps of the fittings. When that fails you get the classic symptom: a drain smell in a bathroom that is rarely used. It is resolved with primary venting to roof level or with air admittance valves where extending the pipe isn’t possible.
Access hatches. Every new stack should be left with accessible hatches at key points. It is the difference between clearing a future blockage in an hour and having to break out tiling again.
The first question to answer is whose pipe it is, because that decides who pays. As a rule, the stack is a communal element of the building and its replacement falls to the residents’ association, while the branch running from the fittings in your flat to that stack is private. When the leak is exactly at the junction, it is worth documenting the source properly before arguing, and there a CCTV survey is worth more than ten opinions.
The second warning concerns the material. In buildings from before 2002 it is common to find asbestos cement stacks. They cannot be cut or broken: removal must be carried out by a company entered in the official asbestos register, with an approved work plan. If it appears, we stop and coordinate the licensed contractor. Quoting an asbestos cement replacement as though it were PVC is a very clear sign that whoever is offering it does not know what they are dealing with.
And a practical recommendation for associations: if the duct has to be opened for one stack, that is the moment to check the others. Opening it again in three years costs the same as opening it today.
Soil stack work we carry out regularly in Alicante and the province:
As a general rule the stack is a communal element and the association covers it; the private branch from each flat’s fittings to the stack is the owner’s responsibility. Disputes usually arise when the leak is at the connection between the two. That is why it is worth documenting the source with a survey before splitting costs: with objective evidence, the discussion is much shorter.
It depends on the route. If the stack runs through a duct accessible from communal areas or through the light well, it can be replaced with almost no access to the flats. If it is buried in bathrooms or kitchens, it has to be opened on every floor, and coordinating with residents becomes the most demanding part of the job: we set a schedule flat by flat, give advance notice and leave each bathroom usable at the end of the day wherever possible.
In a building of five or six storeys, replacing one stack usually takes one to two weeks, including opening up, installing the pipework, testing and making good the tiling and paintwork. Work progresses floor by floor, and what governs the programme is not the work itself but getting access to every flat on consecutive days.
Sometimes: if the leak is local and the rest of the stack is sound, the affected section is replaced. That said, in very old installations a local repair tends to be a short-term fix: if one joint has failed through corrosion or ageing, the others are in the same state and another leak will appear on a different floor within a few years. A CCTV survey helps decide with evidence rather than blindly.
Almost always for one of two reasons: a trap that has dried out through lack of use, solved by running water, or a venting problem where discharges from the floors above siphon the water out of the traps and let the smell through from the stack. The second is corrected by ensuring primary venting to roof level or fitting air admittance valves. If the smell persists and affects several flats, the venting of the whole stack needs reviewing.
Multilayer polypropylene acoustic pipe for stacks inside the building: it substantially reduces flush noise, a common complaint in blocks with old stacks, and installed with resilient brackets it avoids transmitting vibration to the structure. For exterior rainwater pipes and exposed runs, standard PVC drainage pipe performs perfectly well and costs less.