Building near trees

Also see:

4.2.11New drainage

Drainage shall be in accordance with the design and allow for ground movement.

To protect against the effects of heave, drainage should be designed:

  • to take account of potential ground movement as shown in Table 9, including where pipes and services pass through substructure walls or foundations
  • with gradients which may need to be greater than those in Chapter 5.3 ‘Drainage below ground’ as these do not account for possible ground movement
  • to use alternative means of catering for the movement when sufficient falls cannot be provided, for example by deepening the excavation and laying the pipework on a granular bedding of suitable thickness to reduce the extent of potential movement.

Table 9: Volume change potential

Volume change potentialPotential ground movement (mm)


Existing land drains should be maintained or diverted.