A blocked soil stack shows up as toilets that flush slowly, gurgling from baths and basins, and in flats, waste coming up on a lower floor when someone above uses their bathroom. The soil stack is the vertical pipe that takes toilet and bathroom waste down to the drain, and soil stacks are part of the internal drainage we handle under general plumbing. We find where it is blocked, clear it and repair joints that have failed. Call 07427 195142.
What a soil stack does
Every toilet, basin, bath and shower on the upper floors of a house or block drains into the soil stack, which drops down inside or outside the building and turns into the underground drain at the bottom. The top of the stack is usually open above the roof or fitted with an air valve, so air can get in as water falls. That air is what stops the water being sucked out of the traps on each fitting.
Signs the soil stack is blocked
- Several upstairs fittings draining slowly at the same time
- Gurgling from traps when the toilet is flushed
- Waste appearing in a ground floor toilet, bath or shower
- Smells in the bathroom even though the fittings are clean
- In flats, problems in the lowest flat when others use water
Where stacks block
Most blockages sit at the bottom bend, where the stack turns from vertical to horizontal and waste slows down. Wipes, sanitary items and paper build up there until the flow backs up the pipe. The other common spot is a branch connection, where a toilet or bath joins the stack. At the top, a vent blocked by a nest or leaves will not stop waste flowing but will cause gurgling and smells. In a tenement or block of flats, several households share one stack, so what one flat flushes can affect everyone below. If the problem is a smell rather than a blockage, read our guide to a sewer smell in the bathroom.
Clearing a blocked soil stack
We use the access door near the bottom of the stack if there is one, or the first inspection chamber outside, and work from there. Depending on what is in it, the stack is cleared with rods, a flexible auger or high pressure water jetting. Then we run water through the upper fittings and watch it reach the drain. If the bottom bend keeps catching waste, a camera inspection shows whether the pipe or the drain beyond has a fault; see CCTV drain surveys.
Soil pipe leaking or damaged
Older cast iron stacks can crack, and their joints can open as the building moves. Plastic stacks can leak at push-fit joints or where a branch has been badly connected during a bathroom refit. A leaking soil pipe is a hygiene problem and can stain or rot whatever it runs through, so it should be repaired promptly. We replace failed joints or cracked lengths, and where the damage is extensive we discuss replacing a section of the stack. See soil pipe repair and replacement for how that works.
Shared stacks and who is responsible
In a house, the stack belongs to the owner. In flats, the shared part of the stack is usually common property, so a blockage or repair may be a shared cost under your title deeds or factor arrangement. We note where the fault was found so owners can see which section was at fault. If the toilet itself is the problem rather than the stack, see blocked toilet unblocking or toilet repairs.
Questions
How do I know if my soil stack is blocked?
Several fittings slow at once, gurgling when the toilet flushes, or waste appearing on a lower floor all point to the stack rather than one toilet.
Can a soil stack be unblocked without opening the wall?
Usually. We work from the stack's access door or the first chamber outside, so the pipe rarely needs to be opened up.
Who pays for a blocked soil stack in a tenement?
Shared parts of the stack are usually common property, so the cost is often split. Check your title deeds or ask your factor.
Can a leaking soil pipe be repaired rather than replaced?
Often. Failed joints and short cracked lengths can be replaced on their own. Extensive damage may mean replacing a section.