Basement & Cellar Waterproofing and Conversions

Turn a damp cellar into a warm, dry living space, with a waterproofing system designed for your building and guaranteed.

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Experts in Basement & Cellar Waterproofing in London and the Home Counties Since 1971

An unused basement or cellar can become one of the most valuable rooms in your home: a home office, gym, cinema room, guest bedroom or playroom, all without extending your footprint.

Getting the waterproofing right is the foundation of every successful conversion, and it is what Tapco HomeDry has specialised in since 1971.

Why basements get damp

Basements and cellars are built into the ground, so their walls and floors are surrounded by moisture. When the ground is wet, water presses against the structure (known as hydrostatic pressure) and is forced through porous brick, cracks and the joints between walls and floors. A conventional damp proof course is designed to stop moisture rising, not to resist water pushing in from the side, which is why below-ground rooms need a properly designed waterproofing system.

Without one, you can expect damp walls, mould, salts, damaged plaster and decorations, rusting fixings and timber decay, and a musty smell that spreads into the rooms above.

Our basement waterproofing systems

Cavity drain membranes

A studded membrane is fixed to walls and floors, creating a drainage gap. Any water that gets through the structure runs behind the membrane into a perimeter channel and is drained or pumped away. It is the most popular choice for conversions because it copes with old walls and changing water levels.

Tanking

Cementitious tanking applied to sound masonry creates a continuous waterproof barrier bonded to the structure. It can suit smaller areas, light wells and vaults. Read about tanking.

Drainage and sumps

Perimeter drainage channels collect water and lead it to a sump chamber, where an automatic pump discharges it safely away from the building. Backup pumps and alarms protect against power cuts.

For larger or more complex below-ground structures, including new basements and earth-retaining walls, see structural waterproofing.

Cavity drain membrane fixed to basement walls
Basement tanking applied to brick walls
Left: a cavity drain membrane system ready for the internal finish. Right: tanking to a below-ground wall.

Planning your basement conversion

Every basement, cellar and vault is different, and the right solution depends on how the building is constructed and how you plan to use the space. A storage cellar has very different requirements from a bedroom or home cinema. Before work begins, it is worth thinking about:

  • Headroom, and whether the floor needs lowering
  • Access, stairs and escape routes
  • Natural light and light wells
  • Insulation, heating and ventilation
  • Electrics, plumbing and where services will run through the waterproofing
  • Building Regulations, and listed building consent if applicable

We can help you plan from the outset so the waterproofing works with every other part of the project, rather than being an afterthought.

How a basement project works

  1. Survey

    We inspect the space, take moisture readings, assess the structure and discuss how you want to use it.

  2. Design and quotation

    We recommend a waterproofing system, drainage and any pump arrangements, and give you a detailed written quotation.

  3. Preparation

    Old finishes, timber and contaminated plaster are removed and the structure is prepared.

  4. Installation

    Our trained team installs the membrane, tanking, drainage channels and sump as designed, with every detail sealed around services and junctions.

  5. Handover

    You receive your guarantee and servicing advice. We can leave the space ready for your builder or carry out the finishing works.

Projects we’re proud of

Our basement and structural waterproofing work ranges from family homes to some of London’s most demanding commercial buildings, including the Burberry flagship store at 121 Regent Street, basements in Knightsbridge, Marylebone and Notting Hill, and homes across Surrey and the Home Counties. See recent projects.

Why choose Tapco HomeDry?

  • Members of the Basement Waterproofing Association (BWA)
  • PCA-qualified surveyors and over 55 years of experience
  • Systems designed in line with recognised industry standards
  • Our own trained installers, not subcontractors
  • Written guarantees, with Insurance Backed Guarantees available

1971

Established in Thames Ditton

55+

Years of damp & timber expertise

4,000+

Properties visited every year

10

Counties covered across the South East

Why choose Tapco

Basement & Cellar Waterproofing done properly. Diagnosed first, guaranteed after.

Every property gets an individual assessment from a qualified surveyor before anything is recommended.

A little more about us
  1. 01

    Commission-free surveys

    Our PCA-qualified surveyors are not paid commission, so we only recommend the work your building genuinely needs.

  2. 02

    Fixed, written quotations

    After your survey you get a clear written report and a fixed quote, with no hidden extras.

  3. 03

    Our own trained teams

    Our own teams carry out the work, protect your home, keep dust down and leave everything clean.

  4. 04

    Guaranteed for peace of mind

    Written guarantees, which can be protected by an Insurance Backed Guarantee.

Book a survey

Get started today

If you’ve noticed any of these issues, arranging a professional survey is the best way to identify the cause and prevent further damage.

Frequently asked questions

What is the best way to waterproof a basement?

It depends on the building, the ground conditions and how you will use the space. Cavity drain membrane systems are the most widely used for conversions because they manage water rather than resisting it. Tanking suits some situations, and many projects combine both.

What is the difference between damp proofing and waterproofing a basement?

A damp proof course stops moisture rising up a wall. Below-ground walls also have water pushing in sideways under pressure from the surrounding ground, so basements need a waterproofing system designed to cope with that.

Do I need planning permission to convert my cellar?

Converting an existing cellar to habitable space often doesn't need planning permission, but Building Regulations approval is usually required, and listed buildings need consent. Excavating a new basement is a much bigger project. Check with your local authority or an architect.

Do you need a sump pump?

Where water can't drain away by gravity, a sump pump removes it from the drainage channel. We recommend a backup pump or battery, plus an annual service.

Can you work with my builder?

Yes. We can install the waterproofing as a specialist package ready for your builder to complete the fit-out, or manage the specialist works for you.

Is basement waterproofing guaranteed?

Yes. Our systems carry a written guarantee, which can be protected by an Insurance Backed Guarantee for a single premium.

Client testimonials

Tapco really helped me with the issues I had in my house. I found them really helpful, reliable and organised. The team was really polite and gave me a lot of information about what they were doing and how it would help fix the issues. The Tapco guys cleaned after themselves and that is a big plus in my book.

Cosmin
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Serving London, Surrey & the Home Counties

From our offices in Thames Ditton and Esher, our surveyors cover London and the surrounding counties, providing fast response times for residential and commercial properties alike.

We regularly work with:

  • Homeowners
  • Landlords
  • Estate agents
  • Property managers
  • Commercial property owners
  • Housing associations
  • Local authorities

Whether your property requires a damp survey, timber inspection or basement waterproofing system, our experienced team is ready to help.

Map of London and the Home Counties we cover

Our Trusted Accreditations

Our certifications reflect our commitment to the highest standards of work and quality.

Property Care AssociationTrustMarkBasement Waterproofing AssociationSafeContractorCHASAccreditation

Why Tapco

Why choose us

Established in 1971

Choosing Tapco HomeDry means choosing a company with a proven history of protecting properties across the South East.

  • Established in 1971
  • Over 55 years of industry experience
  • Thousands of successful property surveys
  • Honest, practical advice
  • Qualified specialist surveys
  • Comprehensive guarantees
  • Trusted by homeowners and commercial clients

We believe every property deserves an individual assessment. That’s why our recommendations are based on what your building genuinely needs, not unnecessary treatments.

FCA Status Disclosure

Tapco (Preservation) Ltd is an Introducer Appointed Representative (Financial Services Register No. 423558) of Phoenix Financial Consultants Limited (Phoenix). Phoenix is a credit broker, not a lender. Phoenix is authorised and regulated by the Financial Conduct Authority (FRN: 539195), and offers finance from its panel of lenders. All finance subject to status and credit checks.

Finance available on Tapco treatments