London basement excavation,engineered underneathyour existing home.
A directly-employed 25-strong team excavates, underpins and slabs your basement from a live London terrace, with a director on site every day and a 25-year structural warranty on completion.
What proper basement excavation looks like in a London home.
Basement excavation is the structural stage of a basement project: digging out the ground beneath your existing home, underpinning the load-bearing walls in a controlled sequence and casting a new reinforced concrete raft to create a fully usable lower floor. It is heavy civil engineering carried out under a family home, and it is the single most important stage to get right.
What it is
A staged, engineer-designed dig-out beneath your existing structure. We break down the ground floor slab where required, hand-dig and machine-dig in tightly sequenced pins, underpin the foundations, cast a reinforced raft and install waterproofing detail before any conversion work begins.
Who it's for
Homeowners in London who want to add a fully habitable basement floor to a Victorian, Edwardian or period terrace: typically to create a kitchen-diner, cinema room, gym, guest suite or self-contained annex without moving house or losing garden.
When it's needed
When you've outgrown the footprint of your current home, when planning permission caps you above ground, when garden space is precious, and when the value uplift from a properly executed basement outweighs the cost of the works.
Why it matters
Get it wrong and you compromise the structural integrity of your home, your neighbours' homes and your ability to insure and sell the property. Excavation is not a job for a general builder, it is a specialist structural discipline.
Our process
Structured stages, no shortcuts.
Every UHM project runs through the same structured stages. You'll always know what's happening next, who's doing it and when it completes.
01
Free site visit & feasibility
A director visits your home, reviews the existing structure, discusses your brief and gives an honest read on feasibility: whether the party walls, ground and access support a basement excavation.
02
Structural design & party wall
We coordinate with your structural engineer, architect and party wall surveyor to produce a buildable underpinning sequence, method statement and temporary works design.
03
Excavation & underpinning
Our in-house crew executes the dig-out in tightly sequenced pins with continuous temporary works. Muck-away runs on our own schedule, no waiting on third-party hauliers.
04
Raft, drainage & waterproofing
Reinforced concrete raft, integrated drainage, Delta membrane installation and sump-and-pump commissioning: all installed by the same team, tested and signed off.
05
Building control & warranty
Structural sign-off, building control completion certificate and issue of your 25-year structural and waterproofing warranties.
Technical detail
Methods, materials and situations we build for.
Every London basement excavation is site-specific: the ground, the neighbours, the existing structure and the brief all change the design. Here is the toolkit we work with and how it maps to your project.
Underpinning methods we use
The underpinning sequence is the load-bearing decision of a basement dig. We select the method to suit your foundations, your neighbours and your programme, never a one-size-fits-all.
Traditional mass concrete underpinning in sequenced pins
Reinforced concrete underpinning for deeper excavations
Cantilever pin design for party wall constraints
Continuous piled retaining walls where ground conditions demand it
Temporary works propping designed by qualified engineers
Full compliance with CIRIA C760 industry guidance
Materials, plant and muck-away
We operate our own plant and coordinate muck-away through vetted London hauliers on our schedule, not theirs. Concrete is specified to the engineer's mix and poured to certified volumes with slump tests where required.
Mini-excavators sized for London terrace access
Conveyor and skip-lift muck-away systems
Structural mesh and rebar to engineer specification
Grade C32/40 reinforced concrete rafts as standard
Delta membrane systems (Type C cavity drainage)
Twin sump and pump installations with battery back-up
Full dig-out vs partial excavation
Not every home needs a full-depth excavation. Some benefit more from a partial dig: lowering an existing cellar, creating a light-well kitchen or excavating only under a rear extension. We'll tell you which is the right economic call for your property, not just the biggest job we can sell.
Full-depth excavation for new habitable floor
Partial dig-out under existing rear ell
Cellar deepening for utility or storage use
Basement extension beyond the existing footprint (subject to planning)
London ground conditions we work with
South London sits on a mix of London clay, alluvium and made ground. Ground behaviour drives temporary works, dewatering strategy and waterproofing design. Our directors have excavated across Wandsworth, Clapham, Wimbledon, Putney, Balham, Chelsea, Kensington and Richmond upon Thames and know how each ward behaves.
Why it's worth doing properly
Concrete outcomes, not vague claims.
One team, one accountability
The crew who quotes is the crew who digs, underpins, waterproofs and hands over, the same faces on your site from day one to sign-off.
25-year structural warranty
Every completed excavation carries a 25-year structural warranty. The paperwork is real and the company behind it has been trading since 2009.
Programme discipline
Our own labour and in-house plant mean we hit the sequences on the programme we quoted.
Neighbour management
Considerate Constructors scheme members. Party wall coordination handled properly. Deliveries and muck-away scheduled around school runs and residential parking.
Insurance & compliance
£10M all-risks insurance covering public and employers' liability. SSSTS, SMSTS, temporary works co-ordinator and confined space trained team leaders.
Handover you can sell against
A basement built by UHM comes with the certification, warranty and paper trail your solicitor and buyer's surveyor will actually want to see.
The real cost of the wrong contractor
The cost of the wrong basement contractor is not the quote, it's the aftermath.
London basements go wrong in predictable ways: cheap underpinning sequences, unmanaged party wall exposure, waterproofing bolted on as an afterthought and contractors who disappear the moment the money's paid. Every one of those failures is expensive to rectify once the concrete has cured.
Structural movement
Underpinning out of sequence or with insufficient temporary works causes settlement in your home and your neighbour's. Cracks in walls, doors that no longer close, and remedial engineering costs that dwarf the original saving.
Party wall disputes
London terraces sit tight to their neighbours. A contractor that doesn't manage party wall surveyors, method statements and access properly creates disputes that stall the job for months and add legal costs.
Water ingress after completion
Waterproofing designed and installed by the same team that dug the hole avoids the classic handover failure: a basement that passes building control on day one and leaks in month six.
Common homeowner mistakes.
01
Choosing on price alone: the cheapest quote almost always leaves the waterproofing, muck-away or temporary works short.
02
Hiring a general builder who treats the dig as just another job on the list.
03
Assuming planning permission is the hard part, it isn't. Party wall and structural design is.
04
Skipping the structural warranty and Delta-registered waterproofing warranty on completion.
05
Not asking to visit a live site or a completed project before signing.
06
Signing a light specification and letting the contractor upsell every variation once the ground floor is out.
Frequently asked
Real answers, before you call.
Straight answers we give on almost every free site visit, cost, timeline, guarantees and what's included.
Every UHM project is priced per project: there are no fixed prices, because ground conditions, depth, party wall complexity and specification all change the number. What we can promise is that the site visit and written quote are always free, and the quote we send is the number we build to.
How long does the excavation stage take?
The dig-out and underpinning stage typically runs three to six months in a standard London terrace, depending on depth, access and party wall complexity. The full basement project, excavation through conversion, usually completes in 9 to 14 months. Your programme is set in the written quote.
Do you handle party wall notices and awards?
We coordinate with your appointed party wall surveyor and support the process with method statements, temporary works designs and drawings. We don't act as the surveyor, that role stays independent, as it should, but we make sure the technical detail they need is ready on time.
What warranty do I get after excavation?
Every completed UHM basement carries a 25-year structural warranty and a 25-year waterproofing warranty (as Delta Registered Installers). Both are backed by Underhouse Management Ltd, trading since 2009.
Are you fully insured?
Yes. We carry £10,000,000 all-risks insurance covering both public liability and employers' liability. Documentation is provided to your solicitor and building control on request.
Which parts of London do you excavate in?
London only, primarily South London: Wandsworth, Clapham, Wimbledon, Putney, Balham: with regular work in Chelsea, Kensington and Richmond upon Thames. Our workshop is in Tooting (SW17), so response times are fast.
What accreditations do you hold?
FMB accredited members, Delta Registered Waterproofing Installers and members of the Considerate Constructors Scheme. Both directors hold NVQ Level 6 Site Management. The wider team holds SSSTS, SMSTS, Asbestos Awareness, Confined Space Training, First Aid, Temporary Works Co-ordinator and Face Fit certification.
Can I visit a completed or live project?
Yes. Site visits to completed projects are welcome, arrange it through your free consultation. Live-site visits are managed carefully around health-and-safety and client privacy, but can be arranged where appropriate.
