What Are Subsoil Drainage System?

Subsoil Drainage ~ Building Regulation C2 requires that subsoil drainage shall be provided if it is needed to avoid:-

a) the passage of ground moisture into the interior of the building or
b) damage to the fabric of the building.

Subsoil drainage can also be used to improve the stability of the ground, lower the humidity of the site and enhance its horticultural properties. Subsoil drains consist of porous or perforated pipes laid dry jointed in a rubble filled trench.

Porous pipes allow the subsoil water to pass through the body of the pipe whereas perforated pipes which have a series of holes in the lower half allow the subsoil water to rise into the pipe.

This form of ground water control is only economic up to a depth of 1„500, if the water table needs to be lowered to a greater depth other methods of ground water control should be considered.

The water collected by a subsoil drainage system has to be conveyed to a suitable outfall such as a river, lake or surface water drain or sewer.

In all cases permission to discharge the subsoil water will be required from the authority or owner and in the case of streams, rivers and lakes, bank protection at the outfall may be required to prevent erosion.

Subsoil Drainage Systems ~ the lay out of subsoil drains will depend on whether it is necessary to drain the whole site or if it is only the substructure of the building which needs to be protected.

The latter is carried out by installing a cut off drain around the substructure to intercept the flow of water and divert it away from the site of the building. Junctions in a subsoil drainage system can be made using standard fittings or by placing the end of the branch drain onto the crown of the main drain.

NB. connections to surface water sewer can be made at inspection chamber or direct to the sewer using a saddle connector † it may be necessary to have a catchpit to trap any silt.

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