Also see:
5.34.2.11 New 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 potential | Potential ground movement (mm) |
|---|---|
| High | 150 |
| Medium | 100 |
| Low | 50 |
Notes
Existing land drains should be maintained or diverted.
Where the void beneath a suspended floor is liable to flooding, adequate drainage should be provided to take away any flood water.
Last updated: 2nd January 2024