Foundation Design London — Site-Specific Design for Extensions, Underpinning and New Builds

Homeowners extending their property, developers building new structures, and property owners whose existing foundations are causing concern. Also for architects needing a structural engineer to complete the foundation design element of a Building Control submission. If your project involves breaking new ground, increasing loads on existing foundations, or addressing subsidence and settlement, you need a site-specific foundation design.

The foundation transfers the entire weight of a structure into the ground. Its design depends on ground conditions, the nature of the loads, proximity to drainage, trees, and adjoining structures — and these vary considerably across London.

Incorrect foundation design is the most costly structural failure to correct. Remediation typically involves underpinning, which is both disruptive and expensive. Getting the foundation design right at the outset is significantly cheaper than correcting it later — and a properly designed foundation is a condition of Building Control approval.

London's ground conditions vary considerably. Inner-city areas frequently contain made ground and buried infrastructure — old basements, drainage, and filled ground that may not support a standard strip foundation. Much of South and East London is underlain by London clay, which shrinks in dry conditions and swells when wet — particularly relevant near trees. North and West London have varying strata from gravel river terraces to chalk in the far south. We design foundations appropriate to the specific site, incorporating ground investigation findings where available.

Tree root activity in London clay is one of the most common causes of foundation movement in London residential properties. Tree roots extract moisture from the ground, causing seasonal shrinkage and swelling. Foundations too close to trees — or too shallow in active clay — will move with the seasons, causing cracking and potential structural damage. We assess clay heave risk and design foundations to the appropriate depth, referencing NHBC guidance and British Standard recommendations for tree species, distance, and clay type.

Where existing foundations are inadequate — due to subsidence, increased loading from an extension above, or proximity to new excavations — underpinning may be required. We design underpinning sequences that are safe, practical, and buildable, with method statements and phasing drawings to guide the contractor on site. Traditional mass-fill underpinning and mini-pile systems are both within our scope depending on access and site conditions.

Building Control requires foundation design calculations and drawings as part of any extension or new-build submission. We prepare the full foundation design package — calculations, drawings, and specification — coordinated with the structural frame design and the architect's layout. We also respond to Building Control queries after submission as standard.

Civil engineering design (drainage, SuDS, retaining walls and external works) and planning application support are available alongside this structural package, so the below-ground and planning elements of your project can be coordinated with the structural design under a single appointment.