NHBC Standards 2006

5.3 Drainage below ground


5.3 - M1Materials standards
5.3 - M2Drainage materials

5.3 - M1
All materials shall:
(a) meet the Technical Requirements
(b) take account of the design

Materials that comply with the design and the guidance below will be acceptable for drainage below ground.

Materials for drainage below ground should comply with relevant standards, including those listed below. Where no standard exits, materials should carry a certificate of assessment from an independent authority, acceptable to NHBC. Materials of a higher standard are also acceptable.

References to British Standards and Codes of Practice include those made under the Construction Products Directive (89/106/EEC) and, in particular, appropriate European Technical Specifications approved by a European Committee for Standardisation (CEN).


5.3 - M2
All materials for drainage work shall ensure satisfactory service for the life of the system

Items to be taken into account include:

manholes, chambers, pipes, fittings and covers
BS 65Specification for vitrified clay pipes, fittings, joints and ducts (Note: This includes perforated pipes)
BS 437Specification for cast iron spigot and socket drainpipes and fittings
BS 1247Specification for manhole step irons
BS EN 588Fibre cement pipes for sewers and drains.
BS 4660Specification for unplasticised PVC underground drain pipes and fittings
BS 4962Specification for plastics pipes for use as light duty sub-soil drains
BS 5911Precast concrete pipes, fittings and ancillary products
BS 5955Plastics pipework (thermoplastic materials)
BS 6087Specification for flexible joints for cast iron drainpipes and fittings (BS 437) and for cast iron soil, waste and ventilating pipes and fittings (BS 416)
BS DD 76Draft for Development, Precast concrete pipes of composite construction
BS EN 124Gully tops and manhole tops for vehicular and pedestrian areas
BS EN 295Vitrified clay pipes and fittings and pipe joints for drains and sewers
BS EN 1401-1Plastics piping systems for non-pressure underground drainage and sewerage - Unplasticized poly (vinyl chloride) (PVC-U)


  • Group 1 - Areas which can only be used by pedestrians and pedal cyclists.
  • Group 2 - Footways, pedestrian areas and comparable areas, car parks or car parking decks.
  • Group 3 - For gully tops installed in the area of kerbside channels of roads which when measured from the kerb edge, extend a maximum of 0.5m into the carriageway and a maximum of 0.2m into the footway.
  • Group 4 - Carriageways of roads (including pedestrian streets), hard shoulders and parking areas, for all types of road vehicles.

Covers used for manholes within buildings should be airtight and mechanically secured.

Covers used for septic tanks, cesspits and settlement tanks should be lockable.


  • Grade B - for use in carriageways of roads with cars and slow moving normal commercial vehicles
  • Grade A Class 2 - for use in carriageways of roads
  • Grade A Class 1 - for use in carriageways of roads (gully grids of permanent non-rock design).
bricks and blocks

Clay bricks for manholes should comply with BS EN 771 and:

  • be of low active soluble salt content
  • have a compressive strength not less than 48N/mm2.

Engineering bricks are suitable.

Concrete bricks to BS EN 771 should have a minimum crushing strength of 48N/mm2 with a minimum cement content of 350kg/m3 for foul drainage.

Calcium silicate bricks should comprise strength class 20 or above for foul drainage situations.

backfill and bedding

Granular backfill and bedding material should comply with the requirements of BS EN 13242, BS 5955 and BS EN 752, as specified.

Rigid pipes of nominal size 100mm and 110mm nominal flexible pipes should have granular material bedding to BS EN 13242 of 4/10mm pipe bedding gravel. Rigid pipes of nominal size 150mm and 160mm nominal flexible pipes should have granular material bedding to BS EN 13242 of 2/14mm pipe bedding gravel. See Sitework clause S4 (a).

Proprietary pipe systems should be supported and bedded in accordance with the manufacturer's recommendations.