Entry 36 · Conservatories & Exteriors
Drains and gullies near a new conservatory
How to check, clear and maintain drains and gullies around a conservatory base, including warning signs, access covers and when to call a specialist.
A conservatory base usually has one or two gullies or channel drains that take rainwater from the roof and any adjacent paving. If water stands in them, or the ground around the base stays wet after rain, the drain is not doing its job and the base, the DPC and the adjoining wall are at risk. The first check is simple: lift the grate, look for silt, leaves or a standing water level, and note whether the water drains away within a few minutes.
Most conservatory gullies are shallow, with a trapped gully pot and a short run to a soakaway or a connection into the surface water system. When the pot fills with grit and organic matter, the trap still holds water but the outlet is restricted, so the gully overflows at the grate rather than backing up inside. A blocked gully drainage problem of this kind is often visible as a damp band on the paving, a green film on the base brickwork, or a persistent puddle that does not clear. The same principle applies to any trapped gully: the water has to leave the pot before it can leave the site.
01 What does a conservatory gully actually do?
A gully at a conservatory base collects surface water from three places: the conservatory roof outlets, the paving or decking that falls towards the base, and any ground water that reaches the lowest point of the excavation. It is not a foul drain and it should not receive soil pipe connections or washing machine waste. The gully has a removable grate, a silt bucket or pot, and a trapped outlet. The trap holds a water seal that stops smells and vermin from the run, and the outlet connects either to a soakaway, a rainwater pipe, or a combined system.
On older properties the conservatory may have been added over an existing yard gully, which then serves both the new base and the original paving. That is legal if the gully still has capacity and the falls are correct, but it is a common source of confusion when the grate sits inside the conservatory footprint or tight against the base. If the grate is inside the conservatory, it should be a sealed, screw-down cover, not an open grate, because an open gully inside a habitable space lets water vapour and smells into the room.
02 What are the warning signs that the gully is failing?
Standing water in the pot after rain is the first sign. A working gully should be empty within a few minutes of the rain stopping, apart from the normal trap seal. If the water level sits at the grate, the outlet is restricted. If it sits below the grate but does not fall, the trap or the run is blocked further along.
Other signs are less obvious. A damp patch on the internal floor near the base, or a musty smell in the conservatory, can indicate that water is tracking under the base rather than leaving through the gully. Efflorescence, the white salt bloom on brickwork or render, often appears where water has been sitting against the base. Sinking or hollow-sounding paving next to the gully suggests that the sub-base has been washed out by a leaking run. In winter, a gully that freezes and cracks its pot will leak into the ground around the base, and that is a repair, not a clearance job.
03 How should a conservatory gully be cleared and checked?
Start with the grate and the silt bucket. Lift the grate, remove the bucket if there is one, and empty it into a bag rather than onto the paving. Wear gloves, because gully silt can contain sharp glass, metal fragments and bacteria. Hose the bucket and the pot, then check the outlet by pouring a bucket of water in and watching the level. If the water drains freely, the problem was the silt. If it stands, the restriction is in the trap or the run.
For a trapped gully, the next step is to remove the trap or use a drain rod with a rubber plunger. Do not use caustic soda in a gully that serves a soakaway or a surface water run, because it kills the biological activity in the soakaway and can damage the pot. If the run is longer than a few metres, or if there are bends, a drain camera is the only way to see whether the pipe is silted, root-infested or broken. A CCTV survey also records the condition for insurance and for any later dispute with a neighbour about shared drainage.
After clearing, test the falls. Pour water onto the paving around the base and watch where it goes. It should reach the gully, not pool against the DPC. If the paving falls away from the gully, no amount of clearing will solve the problem, and the levels need to be corrected.
04 When is a clearance not enough?
A gully that blocks repeatedly, or that backs up within weeks of being cleared, has a defect rather than a maintenance problem. Common causes are a broken pot, a displaced or collapsed run, roots entering at a joint, or a soakaway that has silted up and no longer accepts water. A soakaway that has failed will show as a gully that drains slowly in wet weather and then overflows in a storm.
In those cases the options are a local repair, a replacement of the run, or a no-dig lining. A local repair is cheapest but only works if the defect is isolated and the pipe is otherwise sound. Replacement means excavating the run, which is disruptive next to a conservatory base because of the foundations and the paving. No-dig techniques, including lining and patch repairs, avoid excavation but need a clean, structurally sound host pipe and a clear access point at both ends. The decision should be based on a camera survey and, where a soakaway is involved, a percolation test to confirm that the ground still accepts water.
05 What maintenance keeps a conservatory base dry?
Clear the grate and bucket twice a year, in spring and late autumn, and after any storm that brings leaves or grit onto the paving. Check the trap seal in dry weather by pouring a jug of water into the gully, because a dry trap lets smells through. Keep the paving falls clean and repair any hollows, since standing water on the paving will find its way to the base even if the gully is clear.
If the conservatory has a rainwater pipe that discharges onto the paving rather than into a gully, consider a shoe or a spreader to direct the flow, and check that the discharge point is not against the base. For a gully that serves a shared run with a neighbour, keep a record of every clearance, with the date and what was removed, because shared drainage disputes often turn on maintenance history rather than on the original installation.
Finally, know where the run goes. A conservatory gully that connects to a soakaway needs the soakaway checked every few years, and one that connects to the surface water sewer needs the connection confirmed, not assumed. If the run cannot be traced, a camera survey and a dye test will establish the route, and that record is worth keeping with the deeds.
One further check belongs with the threshold survey rather than the frame itself. Where a step-free door opens onto a conservatory base, the ground beside it decides how the threshold performs in wet weather. Rainwater, gullies, downpipes and drains around that base should be inspected before the frame goes in, and a blocked gully can be identified by standing water, silt at the grating or damp staining on the plinth. The Sash and Frame Ledger keeps a related entry on drains beside a conservatory that sets out what to survey and what a blocked gully looks like before it floods.