It is mandatory that a qualified professional engineer design the footing systems for Class E and Class P soils.
Class E sites: Class E sites contain extremely reactive clays, which have reactive depths down to four metres below the natural ground level. Footing requirements for Class E sites invariably result in stiffened raft slab construction with deep edge beams and substantial steel reinforcement cages.
Class P sites: These are problem sites, with problem soils due to the following:
- previous use as a rubbish dump
- uncontrolled fill
- loose sand
- proximity to large trees
- soft clay
- landslip potential
- previous land use
- mine subsidence
- swampy areas
- proximity to sewer mains
- potential erosion.
Sites with inherent low allowable bearing pressures will be unable to support the loads imposed by a house structure via the footings. The building will suffer damage if constructed on low bearing soils.