Rainwater drainage is the whole system of gutters, pipes and provisions that carries rainwater away from the roof and paving in a controlled way. Below are practical examples of how this is solved.
Examples of drainage systems
- Box gutter with downpipe — a timber or zinc box gutter along the eaves, draining through one or more downpipes to the sewer or garden. As a rule of thumb, one standard downpipe (Ø 70–100 mm) is often used per roughly 40–80 m² of roof area.
- Half-round gutter — a half-round gutter on brackets fixed to the fascia board, common on many houses.
- Internal flat-roof drainage — an outlet through the roof build-up, always combined with an emergency overflow in case the main outlet blocks.
- Concealed gutter — a gutter hidden out of sight behind the roof edge.
Disconnection and infiltration
Increasingly, rainwater is not sent to the sewer but disconnected and infiltrated into the ground:
- Gravel trench — a gravel-filled trench in which the water seeps away
- Infiltration crates — plastic crates underground with a large void volume
- Blue roof or green roof — buffers water on the roof and releases it slowly
Points of attention
- Provide enough fall in the gutter (about 1–2 mm per metre) towards the outlet
- Fit a leaf guard at the top of the downpipe against blockages
- With infiltration, keep a distance from the façade to avoid damp problems
Related terms
- Rainwater drainage
- Box gutter
- Half-round gutter
- Emergency overflow
- Gravel trench
- Blue roof
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