4.3.6 Services and drainage
All strip and trench fill foundations shall be installed to:
- adequately protect existing services and groundwater drainage
- make allowance for drainage and other services.
4.3.6.1 Adequately protect existing services and groundwater drainage
Any existing services, such as cables, water pipes or gas mains, may need to be supported and protected. Services should not be rigidly encased in the foundations, and drains which are redundant should be cut open and filled or removed. Precautions should be taken to accommodate the effects of settlement where drains run under, or near to, a building.
Provision should be made to divert or protect any existing groundwater drains affected by excavation work, see Figure 3.
4.3.6.2 Make allowance for drainage and other services
Where services are to pass through or above foundations, provision should be made for suitable ducts or lintels to enable later installation.
Strip foundations
Services should not pass through strip foundations but through the masonry above. Adequate lintels should be provided in the masonry.
Trench fill
The load-bearing capability of foundations should not be affected where services pass through. Services should be either sleeved (Figure 4) or pass through a suitably strengthened opening in the foundation (Figures 5 and 6). This is to ensure that differential movement will not damage services.
For drainage, it is important to leave sufficient space for movement to ensure that the drain is capable of maintaining line and gradient.
Figure 4: Over-sized pipe cast as sleeve within foundations

Figure 5: Opening left in masonry above or near the top of foundation with lintel over

Figure 6: Opening left within deep trench fill foundation for service penetration

Last updated: 2nd January 2025