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FMB  ·  Delta Registered  ·  £10M Insured  ·  25-Year Warranty
UHM Basements
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Basement Excavation · London

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.

150+ basements excavated across London · Free site visit and written quote · £10M all-risks insurance.

UHM Basements site hoarding on a London street, active basement excavation project under Considerate Constructors scheme
150+
Basements excavated
30 yrs
Combined experience
25 yr
Structural warranty
£10M
All-risks insurance
25
Strong in-house team
Recent work

Recent projects, delivered by UHM.

UHM Basements London project 1
UHM Basements London project 2
UHM Basements London project 3
UHM Basements London project 4
UHM Basements London project 5
UHM Basements London project 6
UHM Basements London project 7
UHM Basements London project 8
UHM Basements London project 9
UHM Basements London project 10
UHM Basements London project 11
UHM Basements London project 12
UHM Basements London project 13
UHM Basements London project 14
View the full portfolio →
Service overview

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.

  1. 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.

  2. 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.

  3. 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.

  4. 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.

  5. 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.

How much does a London basement excavation cost?

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.

Related services

Explore the full basement discipline

Where we work

Serving South London first

Book your free site visit

Ready to dig beneath your London home? Let's walk it through in person.

A director will visit your home, review your architect's drawings, and give you a written quote, for free. No pressure, no obligation, no upsell.

  • Free site visit
  • Free written quote
  • 25-year warranty
  • £10M insurance
  • Directly-employed team

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