Technical Booklet C Site Preparation and Resistance to Contaminants and Moisture·Page 20·4.1, 4.2
Subsoil drainage - general provisions and flooding assumptions
The building site and adjacent ground are assumed not to be subject to flooding. Where the water table could rise within 250 mm of the lowest damp proof membrane or surface water could affect the building, gravity drainage or other effective safeguards must be provided.
4.1 The provisions that follow assume that the site of the building and the ground adjacent to it is not subject to flooding.
4.2 Where the water table can rise to within 250 mm of the lowest damp proof membrane (DPM) of the building, or where surface water could enter or adversely affect the building, either the ground to be covered by the building should be drained by gravity, or some other effective means should be taken to safeguard the building.
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