What is a balcony drain?
A balcony drain is the body and grating built into a balcony floor to take rainwater away. In the Netherlands the brand name pluvetta is used generically for these outlets, much as a proprietary name becomes a household word.
Two types
- Outlet with a pipe connection. Used on the top-floor balcony. Water enters the body and is carried away through a pipe.
- Through-flow grating. Used on intermediate-floor balconies. The water falls straight through onto the balcony below, and so on down to the lowest level where it is collected.
The through-flow version is cheap and simple, but it has a downside: one blockage at the top puts the whole stack under water, and in windy weather the falling water blows against the facade and across the balconies.
| Outlet with a pipe connection | Used on the top-floor balcony. Water enters the body and is carried away through a pipe. |
|---|---|
| Through-flow grating | Used on intermediate-floor balconies. Water falls straight through to the balcony below and is collected at the lowest level. Cheap and simple, but one blockage at the top puts the whole stack under water, and in windy weather the falling water blows against the facade and across the balconies. |
Detailing and points to watch
- Falls. A balcony floor must slope towards the outlet. As a rule of thumb a fall of roughly 1 to 2 per cent is used — towards the outlet and away from the facade. Without a fall, water ponds; that brings soiling, algae, frost damage and eventually leaks.
- Access. An outlet you cannot clean will block. Choose a grating that lifts out without tools, and agree who cleans it and how often — leaf fall in autumn is the main cause of blockage.
- Junction with the waterproofing. The outlet must be dressed into the waterproofing layer with a flange or sleeve. This detail is by some margin the most common leak point on a balcony. Drains for buildings are covered by BS EN 1253.
- Overflow. On an enclosed balcony with an upstand, the water needs somewhere to go if the outlet blocks. A spout or overflow opening in the upstand prevents the structure being loaded by standing water.
- Frost. A pipe run externally along the facade can freeze. Take that into account when routing it.
Related terms
- Balcony
- Rainwater drainage
- Gutter
- Spout
- Fall
Want to learn more about construction terms? Visit our knowledge base at fredsdiyplans.com.