How Much Do Basements and Underpinning Cost in London?
Real design-and-build rates, not guesswork. Because EMA Structures designs and carries out below-ground works with one team, here are our indicative 2026 construction costs and what moves them.
In short: as indicative design-and-build figures including labour and materials, basement construction costs around £3,500 per m² for excavation up to about 3.5 m deep on basements up to around 50 m², with smaller basements closer to £4,200 per m², and wall underpinning with 1 m deep pins costs around £1,500 per metre run. Ground conditions, access and the existing structure move these figures, so every job is priced from a site-specific assessment and confirmed in writing. Tell us about your project and we will give you a real number.
Indicative construction rates
Most cost guides online are written by practices that only design, so their construction figures are second-hand. EMA Structures both engineers and builds below-ground works, which is why we can publish our own rates. All figures include labour and materials and exclude VAT.
| Works | Basis | Indicative cost |
|---|---|---|
| Basement construction | Labour and materials, excavation up to about 3.5 m deep, basements up to around 50 m² | ~£3,500 per m² |
| Basement construction, smaller footprint | Below roughly 50 m², the fixed costs of set-up, propping and waterproofing spread over less area | ~£4,200 per m² |
| Wall underpinning | Labour and materials, underpinning pins to 1 m deep, per metre run of wall | ~£1,500 per metre |
Indicative figures only, correct as of July 2026 and reviewed periodically. Every basement and underpinning job is priced from a site-specific assessment and confirmed with a written quotation before work begins.
Why smaller basements cost more per square metre
A large share of a basement's cost is fixed whatever its size: setting up the site, temporary propping, getting excavation access into a London property, the waterproofing system, and connecting drainage and services. On a bigger footprint those fixed costs spread across more floor area, so the rate per square metre falls. On a small basement the same set-up is divided across less area, which is why the indicative rate moves from around £3,500 to around £4,200 per m². In other words, a small basement is not proportionally cheap, and a larger one is often better value per square metre.
What moves basement costs up or down
- Ground conditions and water. London clay behaves differently from gravels, and a high water table changes the excavation approach, the waterproofing strategy and the programme.
- Depth. The rates above assume excavation up to about 3.5 m; going deeper changes the engineering and the temporary works.
- Access. Terraced streets with no side access mean spoil comes out through or over the building, which slows everything down.
- The existing structure. Older foundations, previous alterations and party walls all affect the underpinning sequence and the temporary support required. Where the foundations are unknown, trial pits settle it before design is finalised.
- Party wall constraints. Basement works next to neighbouring properties usually engage the Party Wall etc. Act 1996, which affects sequence and programme.
- Finish level. The rates above are for the structural shell and waterproofing, not fit-out.
Underpinning: diagnose before you dig
Underpinning is a significant structural intervention, and it is the wrong answer to some types of movement. Cracking caused by thermal movement or decayed lintels does not need underpinning, and underpinning a foundation that was never the problem wastes serious money. That is why the process starts with a structural inspection to diagnose the cause, and only then a designed underpinning scheme, sequence, depths and calculations for Building Control. Our guide to when underpinning is needed covers the warning signs and the alternatives.
The ~£1,500 per metre run figure covers traditional mass-concrete underpinning with pins to 1 m deep, dug and cast in a controlled sequence. Deeper pins, difficult access or live movement change the price, which is why it is always confirmed after inspection.
One team from design to dig
Because EMA Structures provides the engineering design for basements and underpinning and carries out the works with our own site team, the design is drawn to be built, the price reflects how the job will actually be sequenced, and there is one point of responsibility from first inspection to completed structure. For the engineering fees side, design packages, calculations and inspections, see our guide to what a structural engineer costs in London.
Getting a real number
Send us your drawings, photos or a description of the project and we will confirm what the works involve and give you a written, site-specific quotation, with the scope, the assumptions and the programme, so there are no surprises once the digging starts.
All figures on this page exclude VAT, are indicative design-and-build rates correct as of July 2026, and are subject to site-specific assessment. Every engagement is confirmed with a written quotation setting out the scope, price and terms before work begins.
Basement and underpinning cost questions
How much does a basement cost per square metre in London?
As an indicative design-and-build figure for excavation up to about 3.5 m deep, basement construction costs around £3,500 per square metre including labour and materials for basements up to around 50 square metres. Smaller basements typically run closer to £4,200 per square metre because the fixed costs of setting up, propping and waterproofing spread across less floor area. Every basement is priced from a site-specific assessment.
How much does underpinning cost in London?
As an indicative design-and-build figure, wall underpinning with 1 m deep pins costs around £1,500 per metre run including labour and materials. The final cost depends on ground conditions, access and the length of wall affected, so it is always confirmed by a site-specific quotation following an inspection.
Why do smaller basements cost more per square metre?
Much of a basement's cost is fixed regardless of size: setting up the site, temporary propping, excavation access, waterproofing systems and connecting services. On a larger footprint those fixed costs spread across more floor area, bringing the rate per square metre down. On a small basement the same set-up costs are divided across less area, which is why the indicative rate rises from around £3,500 to around £4,200 per square metre.
Do I need a structural engineer before underpinning?
Yes. Underpinning is a significant structural intervention and the wrong response to some types of movement, so the cause should be diagnosed first. A structural engineer confirms whether underpinning is actually needed, designs the underpinning sequence and depth, and provides the calculations Building Control require. At EMA Structures we diagnose, design and can also carry out the works as one team.
Planning a basement or worried about foundations?
Send us your drawings, photos or a description of the project and we will give you a written, site-specific quotation, no obligation.