NHBC Standards 2006

4.5 Raft, pile, pier and beam foundations


4.5 - M1Material standards
4.5 - M2Concrete
4.5 - M3Reinforcement
4.5 - M4-M5Other materials

4.5 - 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 raft, pile, pier and beam foundations.

Materials for raft, pile, pier and beam foundations should comply with all relevant standards, including those listed below. Where no standard exists, Technical Requirement R3 applies (see Chapter 1.1 'Introduction to the Standards and Technical Requirements').

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).


4.5 - M2
Concrete shall be of a mix design which will achieve the required strength and be sufficiently resistant to chemical and frost action

For guidance on the specification and use of concrete, particularly in relation to the choice of mix to achieve sufficient structural strength and resist deterioration due to ground aggressivity and frost action, reference should be made to Chapter 2.1 'Concrete and its reinforcement' (each section).


4.5 - M3
Reinforcement shall be sufficient to ensure proper transfer of loads

Reinforcement shall be in accordance with Chapter 2.1 'Concrete and its reinforcement' (each section).


4.5 - M4
Compressible materials shall be capable of absorbing potential heave forces, where appropriate

Proprietary materials should be either assessed in accordance with Technical Requirement R3 or acceptable to NHBC through established custom and practice.

4.5 - M5
Sealing materials for movement joints shall be suitable for their intended purpose

Joints often fail because the likely variation in the size of the joint is not compatible with the movement capability of the sealing material.

Factors to be taken into account when choosing materials for movement joints should include:

  • designed joint width
  • actual joint width
  • joint depth
  • anticipated movement
  • movement capability of seal
  • surface preparation
  • backing medium
  • projected life span of joint.

Sealants should be such that there is good adhesion between the sealant and the material either side of the joint.

Back up material should be resilient and should not adhere to, or react with, the sealant.

The compressibility of the sealant back-up/joint filler is possibly the most critical factor in the design of an adequate joint for fired clay brickwork.

A pressure of about 0.1N/mm2 should be sufficient to compress the material to 50% of its original thickness. Flexible cellular polyethylene, cellular polyurethane or foam rubbers are the most satisfactory materials for backing to movement joints in fired clay brickwork.

Hemp, fibreboard, cork and similar materials are suitable for movement joints in concrete, but should not be used for expansion joints in fired clay brickwork.