The gutter, outlet, downpipe and drainage parts that collect roof water and take it safely away.
Rainwater drainage, also called surface water drainage, collects the clean water that falls on roofs and paved areas and carries it away before it can soak into the building or pond around it.
At roof level, gutters run along the eaves to catch water shedding off the roof. The gutter is laid with a slight fall towards its outlets so water keeps moving rather than standing.
At each outlet, a downpipe takes the water vertically down the wall. Sizing the gutters, outlets and downpipes to suit the roof area and rainfall is what stops them overflowing in a heavy storm.
At the bottom, the water is delivered somewhere suitable: a gully, a rainwater shoe to a surface-water drain, or a soakaway that lets it disperse into the ground. The right destination depends on the site and local drainage arrangements.
Where drainage is separate, this clean surface water is kept apart from foul drainage so that rain does not overload the foul system and so the two flows are handled appropriately.
For revision, picture the journey: roof to gutter, gutter to outlet, downpipe to ground, then to a soakaway or surface-water drain. Confirm sizing and disposal options against Approved Document H.
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