Assessment, design and construction of underpinning across London: foundation stabilisation for basements, extensions and subsidence, carried out by our specialist construction arm in safe, sequenced bays under engineering oversight, with temporary works requirements defined alongside.
Underpinning extends or strengthens existing foundations so they reach more stable ground or carry additional load. It is needed when the existing foundations can no longer support the building adequately, most often after subsidence has undermined the soil, or when a new basement or a deeper adjacent foundation means the existing footings must be taken down further. It is not a default repair: it is appropriate only when the cause of movement has been confirmed and the evidence shows the foundations themselves need to change. Where a problem can be solved by removing its cause, such as repairing a leaking drain, underpinning may not be required at all.
The right method depends on the cause, the ground conditions, the loads and the access available. These are the main approaches we assess and design.
Also known as pit or traditional underpinning. The ground beneath the existing footing is excavated in sequenced bays of about a metre, never more than a third of the wall at once, and filled with sulphate-resisting mass concrete taken at least 150 mm into firm ground, then dry-packed to the old footing. The usual method to around 2.5 m deep; beyond that piles are safer and produce less spoil.
A reinforced concrete beam is introduced beneath or through the wall to span between new bases at roughly 2.5 to 3 m centres, taken down to firm ground typically 2 to 2.5 m below the surface, or between piles. Useful where loads are heavy, soils are variable, or mass concrete would be impractical.
Mini-piles of 300 mm or less, augered in clay, driven in fill and gravels, or jacked in vibration-free against the weight of the building, carry the load to deeper strata through needle beams, cantilever beams or a raft toothed into the walls, with anti-heave sleeves where a tree has been removed. Injected geopolymer resin compacts granular ground and fills voids with almost no excavation. Their suitability depends entirely on the soil and the cause of movement, and they are specified only where ground investigation supports them.
From confirming whether underpinning is justified through to design, approvals support and site review.
Underpinning is as much about how work is staged as the foundation itself. The building must stay supported at every moment.
Because underpinning involves removing support beneath a live structure, the work is carried out in short, alternating sections, often described as a "hit and miss" sequence, so that only a limited length of foundation is ever exposed at once and the load is safely redistributed. The order in which sections are excavated, the maximum open length, curing times for new concrete and the use of temporary support to walls and openings all need to be set out clearly before work begins.
Where the surrounding ground, adjacent structures or deep excavations are involved, temporary works such as propping, shoring or sheet piling may be required to keep the works and neighbouring buildings safe. We define these requirements as part of the design and coordinate with the contractor so they are properly accounted for on site. The contractor remains responsible for temporary works, sequencing and construction methodology unless EMA Structures is separately appointed in writing.
A disciplined route that confirms the need, designs the right solution and oversees safe delivery.
Confirm whether underpinning is justified by reviewing the cause of movement, ground conditions and existing foundations.
Where required, trial pits, soil sampling and a drainage survey to confirm foundation depth and ground behaviour.
Select the method and prepare calculations, drawings, sequencing and temporary works requirements.
Provide the information needed for Building Control, with Party Wall awareness where neighbours are affected.
Our construction team carries out the underpinning in safe, sequenced bays, or we coordinate a specialist contractor on larger schemes.
Inspect the works on site so the underpinning is built in line with the engineering intent.
Underpinning usually follows a movement assessment or supports a basement project. These pages cover the related services.
Movement and subsidence assessment, monitoring advice and repair strategy.
Learn moreEngineering-led repair strategies, specifications and remediation.
Learn moreStructural design for basements, retaining works and basement underpinning.
Learn moreUnderpinning is needed when the existing foundations no longer provide adequate support, for example after subsidence has undermined the ground, or where a new basement or deeper adjacent foundation requires the existing footings to be extended downwards. It is confirmed by a structural assessment, often supported by trial pits and soil investigation. Underpinning should never be assumed before the cause of movement is established.
Underpinning extends or strengthens the existing foundations, usually by working in short, carefully sequenced sections so the structure stays supported throughout. Common approaches include mass concrete (pit) underpinning, beam-and-base underpinning, and geotechnical methods such as resin injection or piling. The right method depends on the cause, the soil, the loads and access, and is selected as part of the design.
Yes. Underpinning is defined as building work under the Building Regulations and requires an application, inspection of the excavations before concreting and a completion certificate. Pinning a party wall, or excavating within 3 m of a neighbour's building to below the level of their foundations, also brings in the Party Wall etc. Act 1996, with notices and usually an award before work starts. We prepare the calculations, drawings and information needed to support both.
Yes. We assess whether underpinning is justified, design the scheme with calculations and drawings, and our specialist construction arm carries out the underpinning in safe, sequenced bays under engineering oversight. For larger or specialist schemes we can instead coordinate trusted specialist contractors, and either way we review the works on site so they follow the engineering design.
A contractor's guarantee, for which ten years is now the norm and insurance-backed is better than a bare company promise, the Building Regulations completion certificate, as-built drawings of the underpinning, and a Certificate of Structural Adequacy from the engineer recording the cause of the movement, the works carried out, the approvals obtained and the inspections made. Keep all of it: insurers, lenders and a future buyer's solicitor will ask for it.
Tell us what you are seeing, or share your basement plans, and we will advise whether underpinning is the right approach.