Underpinning work requires very careful planning and execution. It is usually costly, and will require the services of a structural engineer experienced in underpinning works.
Where it is proposed to underpin an existing foundation, approval under the building regulations will normally be required. Gaining such approval will usually involve the preparation of a structural design of the underpinning, including the process to be carried out during construction.
An initial step, before substantial commencement of the work, will generally be for a trial hole to be dug next to the existing footings for a structural engineer or surveyor to make an assessment of the circumstances of the case.
The reasons for underpinning are generally:
Particular attention will need to be given to any sewers and drains near the work.
Underpinning is a method of construction that sees the depth of the foundations to a building being increased. The soil beneath the existing foundation is excavated and is replaced with foundation material, normally concrete, in phases.
Underpinning requires close attention to design, methodology and safety procedures. If not carried out properly, this kind of work poses very real risks and could see damage to or collapse of the existing home.
Additional Information can be found here: Planning Portal