Balcony drain blocked? Prevent leaks to neighbours

Balconies and roof terraces usually have one of these two types of drain. A spout is a short pipe or opening through the edge or parapet, through which the water falls outside or runs into a downpipe. An internal outlet is a drain gully in the floor, with a pipe that runs down through the structure and connects to a downpipe or a shared drainage pipe. Many balconies also have an emergency overflow: a second, slightly higher opening that drains the water if the main drain is blocked.

Signs of a blocked balcony drain

• After a rain shower, water remains on the balcony longer than normal.
• The water drains away via the overflow, whilst the normal drain remains dry.
• There is a layer of mud, leaves or moss around the drain gully.
• A damp patch appears on the ceiling or along the façade at the downstairs neighbours'. Read more about this in damp patches on the ceiling.
• During heavy rain, water rises up to or under the balcony door.

What causes the drain to become blocked?

• Leaves and flower debris from plant pots and from trees nearby.
• Potting soil and sand that wash out of plant pots after watering.
• Moss and algae that grow on a damp floor and come loose.
• Bird nests or feathers in a spout that's rarely used.
• Debris in the pipe further down, for example in a shared downpipe serving multiple balconies.

Step-by-step plan: clearing the balcony drain yourself

1. Remove standing water. Scoop or sweep away as much water as possible, so you can reach the drain and there's less chance of it running inside.
2. Clean the grating or leaf guard. Remove leaves, soil and moss from the grating or from the dome above the drain. Lift the grating out if possible.
3. Remove debris from the opening. Use your hand (with gloves) or a small scoop to remove debris from the first section of the drain or spout.
4. Flush through with a bucket of water. Pour a bucket of water gently into the drain and see if it runs away freely. Don't use large quantities at once until you're sure it drains properly.
5. Carefully try a hand snake. With a floor drain, a short hand snake can loosen a blockage in the first section. Turn gently and don't push too hard: the connection through the floor is vulnerable.
6. Check the emergency overflow. Make sure it is also clear. It is your reserve if the main drain unexpectedly becomes blocked.

Always work safely. Do not lean over the balcony edge to reach an external spout, and do not stand on a chair or stepladder near the edge. Anything you cannot reach from the balcony floor should be left to a tradesman.

What you'd better not do

• No chemical drain cleaner. It doesn't work against leaves and soil and can damage the roof covering or sealant joints of the balcony.
• Don't poke hard with a stick or screwdriver into the drain. Around the drain there's a connection to the waterproof layer; if you damage it, water can get into the structure.
• Don't block the emergency overflow, not even temporarily, for example with plant pots or a rug.
• Do not leave the problem because the water will eventually drain away. It is precisely slowly draining water that can leak inside unnoticed.

Flat or owners' association: who is responsible?

In an apartment complex, balcony drains are often connected to each other via a shared downpipe or vertical stack. The balcony itself and those pipes are then usually common property of the owners' association (VvE), even though you use the balcony alone. Who is responsible for cleaning and repairs is stated in the deed of division and the regulations of your VvE; this differs per building. If in doubt, contact the manager or board of the VvE before having any work done on the pipe. On our page for VvEs you can read how we work with owners' associations. If the blockage is in the shared pipe, also read about a blocked vertical stack.

Leak at the downstairs neighbours': act quickly

Has the downstairs neighbour reported a damp patch or is water dripping from the ceiling? First make sure no new water is added: remove standing water and stop watering plants. Take photos of the situation on your balcony and at the neighbours', this helps with handling by the owners' association (VvE) or insurer. Then follow the action plan for leaks and call in a tradesman. On the leak page you can read how we trace the cause.

Also watch out in freezing weather

In winter, water in a partially blocked drain can freeze. The ice then completely seals the opening, and when it thaws or rains the water remains on the balcony. Therefore, keep the drain clear especially before winter.

How to prevent a blocked balcony drain

• Sweep the balcony regularly, especially in autumn and after strong winds.
• Place plant pots on feet or saucers, so potting soil doesn't wash towards the drain.
• Use a grate or leaf guard on the drain and clean it regularly.
• After heavy rain, check whether the water drains away quickly.
• Always keep the emergency overflow clear.

Does the water from your balcony run into a downpipe that is itself blocked? Then read downpipe blocked. For drain unblocking in the region, see drain unblocking in The Hague city centre or drain unblocking in Delft.