Drainage

Drainage collects water and carries it away so it does not build up where it should not. Surface drainage gathers rainwater using falls, gutters, slot or grated channels and gullies. Subsurface drainage keeps groundwater away from foundations and basement walls using perforated pipes, gravel and filter fabric.

Drainage in buildings and landscape

In basements, waterproofing alone is not enough. A drainage membrane outside the retaining wall and a perforated pipe around the footing stop water building up pressure. In landscape work, paved areas fall away from the building, and planted areas need soil that lets water percolate. The back of retaining walls, terraces, green roofs and planters all need their own drainage layer. Where the lines discharge has to be decided on the drawings: a storm sewer, a collection tank or a soakaway such as a rain garden. Most problems start not on site but in decisions about levels and falls, which is why drainage should be drawn together with finished levels.

Hidden but decisive

Drainage rarely shows in a visualization, yet grated channels, edge gutters and the joint pattern of paving add convincing detail. If an exterior render is meant to show wet ground after rain, knowing where water would actually collect makes the image more believable.