Footings

There is no one standard footing. The size and depth will be determined from the ground conditions, soil conditions and if you have any trees near or on the footings. Generally a trench fill foundations 600mm wide but the depth would be needed to taken down when finding firm ground, this as said would need to be determined by the structural engineer and to be approved by building control before pouring concrete. Kind Regards Avion Homes

These are generally dug to a depth of 1m deep and 600mm wide, however since cavities got wider to 150mm then really the trench should be made a bit wider. the footings would need to be confirmed via building control first after digging. things that can alter the depth would be trees near by, the plasticity of the soil if clay, and ground type. thanks hanley smith building (worcestershire)

As a general rule, the foundation should project at least 150 mm beyond each side of the wall. For example, if you’re building a 300 mm cavity wall, the foundation should typically be around 650 mm wide. In most cases, the concrete footing itself is around 600 mm deep, with the underside of the foundation positioned at a minimum depth of 900 mm below finished external ground level. This is because, at that depth, clay soils are generally less affected by seasonal expansion and shrinkage caused by changes in moisture and temperature. However, if the ground conditions are poor or there are nearby trees (particularly conifers, which can extract significant amounts of moisture from clay) the foundations may need to be substantially deeper. In some cases, foundations can be required to go 2.5 metres or more below ground level. My advice would be to speak to a structural engineer before starting the foundations. They can provide calculations and specifications, or prepare structural drawings to ensure the foundations comply with Building Regulations.