Soakaway design

Soakaways are to be of hollow construction, using honeycomb brickwork, perforated concrete sections or plastic creates which are readily available from local builders’ merchants. Chamber size depends upon the volume of water to be received, and the porosity of the ground.

Within the Borough of Broxbourne, experience has shown that a soakaway of 1m³ internal capacity below the level of the pipe is a minimum size which is usually sufficient for a domestic extension.

Where a catchment area exceeding 75m² is to be drained, reference should be made to BRE (Building Research Establishment) Digest 365.  This may be available through your local reference library or can be ordered from the BRE bookshop on 01923  664444.

Soakaways should be situated no closer than 5 metres to any building or boundary.  Once the chamber is in place, backfill the surrounding excavation with granular material such as hardcore, to allow effective drainage.

To reduce the risk of flooding, the soakaway should be located downhill from the property unless the ground is very porous.

A reinforced concrete cover for the chamber may be purchased from a builders’ merchant for either a concrete ring or honeycombed brick soakaway.  Alternatively, where the span across the soakaway is no more than 1.0m, one may be constructed of 150mm thick well compacted concrete of 1:2:4 mix, with A142 mesh reinforcement placed 50mm from the bottom.

Plastic creates should be installed in accordance with the manufacturers' recommendations and surrounded with a permeable geotextile membrane. A heavy duty grade must be used if there is to be traffic travellling over.