Substructure and ground-bearing floors

Also see:

5.1.5Services and drainage

Substructure and ground-bearing floors shall be installed to:

  1. adequately protect existing services and ground water drainage
  2. have suitable surface and subsoil drainage
  3. make allowance for drainage and other services.

Adequately protect existing services and ground water drainage

All existing services should be located and identified before work commences. During dry periods it can be difficult to determine if ground water drains are active, so where they are severed or disturbed, they should be reconnected to a suitable outfall.

Existing active groundwater drainage should be retained to minimise the risk of flooding. Water from these drains may require diverting.

Where existing services conflict with the proposed foundations or substructure, and they are to remain, they should be protected or diverted and remaining voids filled with concrete or grout. Where they are no longer active and are not needed, they should be disconnected and grubbed up.

Surface water and subsoil drainage

Surface and/or subsoil drainage may be needed on sites where there is a risk of waterlogging.

Walls which act as retaining walls may require land drains, hardcore fill and suitable outlets to dispose of any subsoil water that collects behind the wall.

Ground or paths adjoining the home should:

  • slope away at a slight fall
  • generally be at least 150mm below the DPC.

Make allowance for drainage and other services

Design information should include all necessary details relating to the proposed underground services.

Drain pipes passing through or under the building may require flexible connections or other means of accommodating differential movement.

Where pipes penetrate walls, they should be provided with flexible joints or be sited in an opening formed by lintels.

Services should be sleeved where they pass through a structural element. Where required, they should be arranged so that future access can be obtained without affecting structural stability.

When unidentified services, ducts, cables or pipes are exposed, advice should be sought from local offices of statutory undertakings and service supply companies.