Leakage in a service duct or shaft
A shaft collects water from every floor it passes, so a leak there affects many flats at once. Because shafts are enclosed and rarely inspected, problems usually run for years before anyone traces them.
Not an emergency, but it will get worse and more expensive with every monsoon it survives.
Probable causes, ranked
Ordered by how often we find each one to be the actual source. The 'tell' is what distinguishes it from the others.
- 01most common
Leaking drainage stack or joint within the shaft
The tell — Damp on shaft-adjacent walls across several floors simultaneously.
Injection Grouting → - 02common
Failed waterproofing at shaft floor penetrations
The tell — Wetting worst at the lowest floors of the shaft.
Bathroom Waterproofing → - 03common
Rainwater entering the shaft at roof level
The tell — Ingress correlates with rain rather than with usage.
Terrace Waterproofing → - 04less common
Condensation in a poorly ventilated shaft
The tell — General dampness with no traceable running water.
Chemical Coating →
Sixty seconds, before you call anyone
- Photograph it while it is actively wet. A dried stain tells a surveyor far less than a running one.
- Note whether it worsens with rain or with usage. Rain-linked points to the building envelope; usage-linked points to plumbing. This single distinction settles most arguments about responsibility.
- Check the area directly above and beside the damage, not only below it. Water travels along a slab before it drops.
- Look specifically for the tell of the most likely cause: damp on shaft-adjacent walls across several floors simultaneously.
- Do not chip into saturated plaster or paint over a damp patch. The first risks bringing material down; the second destroys the evidence needed to trace the path.
What it becomes if you leave it
A shaft leak affects every flat adjacent to it, so the eventual repair is a building-wide scope rather than an individual one. Enclosed, permanently damp shafts also corrode the services running through them.
Often seen alongside this
- Bathroom leaking into the flat below
Water from a bathroom reaching the flat below is almost never a failed membrane across the floor.
- Damp patch spreading on an internal wall
A damp patch on an internal wall means water is reaching the wall from somewhere you cannot see — usually the external face, a concealed pipe, or the slab above.
Leakage in a service duct or shaft — questions we get asked
What is the most likely cause of leakage in a service duct or shaft?
Leaking drainage stack or joint within the shaft. The sign that points to it is: damp on shaft-adjacent walls across several floors simultaneously. That said, the ranking here is a starting point — the actual source is confirmed by survey, because more than one of these can be true at once.
What happens if I leave it?
A shaft leak affects every flat adjacent to it, so the eventual repair is a building-wide scope rather than an individual one. Enclosed, permanently damp shafts also corrode the services running through them.
Can I diagnose this myself before calling anyone?
Partly, and it is worth doing. Photograph it while it is actively wet, note whether it worsens with rain or with usage, and check the area directly above and beside the damage. That single rain-versus-usage distinction narrows the cause more than anything else you can do in sixty seconds.
How urgent is this?
Act this season. Not an emergency, but it will get worse and more expensive with every monsoon it survives.
Send us a photograph and we will tell you what we think it is
WhatsApp a photo taken while it is wet, with a note on whether it tracks with rain or with usage. That is usually enough for a first opinion, and the site inspection that follows is free.
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