Basement Tanking & Waterproofing London

Tanking or cavity drain membrane: which do you need?

Type A barrier protection uses a cementitious slurry or waterproof render bonded to the masonry or concrete. It resists water at the surface, so the background must be sound and the detailing continuous at floors, walls, corners and penetrations. It can suit many cellars and smaller basements, but the structure and expected water pressure must be assessed before specifying it.

Type C drained protection uses a cavity drain membrane with channels and a suitable drainage route, often including a sump and pump. Rather than holding water back at the wall, it manages water entering behind the membrane and directs it away. Drainage access, maintenance and any pump arrangements are part of the specification; pump supply and installation are handled by specialist partners.

The survey decides which approach, or combination, suits the building and intended use. In line with BS 8102, the assessment considers ground conditions, water pressure, structural condition and the consequences of failure. We identify when specialist waterproofing design input is needed rather than treating either system as a universal answer.

Basement tanking services in London

London has a huge stock of Victorian and Georgian houses with cellars and vaults, and a constant flow of lower-ground and basement conversions. We provide:

• Basement tanking for conversions and new basement rooms
• Cellar waterproofing and damp proofing for period properties
• Waterproofing of coal vaults and under-pavement vaults
• Cavity drain membranes with drainage channels, sumps and pumps
• Cementitious tanking to walls, floors and junctions
• Render, screed, plaster and decorative finishes over the completed waterproofing

We work for main contractors, architects and private clients, and alongside structural waterproofing designers and building control on larger basement schemes.

Proven below-ground work: Lancaster Gate

At Lancaster Gate, a three-year heritage restoration of a Victorian building in Bayswater, we brought 13 basement vaults back into use. Structural waterproofing was installed, followed by render and screed throughout. No two vaults were the same size or shape, and the existing brick varied from vault to vault — exactly the conditions where a careful survey and hand detailing matter. The same team carried out 4,000m² of lime plastering, the full external render and the fibrous restoration on the building.

Waterproofing basements to BS 8102

We work to BS 8102, the British Standard code of practice for protecting below-ground structures against water from the ground. It sets out three types of protection — barrier protection (Type A), structurally integral protection (Type B) and drained protection (Type C) — and asks designers to consider the intended use of the space, the water table and the consequences of failure. A storage cellar and a habitable basement bedroom need very different levels of protection.

Where a project has a waterproofing designer or structural engineer, we install to their specification. Where it does not, we survey and recommend a system, and will tell you when a project needs specialist design input.

Cellar waterproofing for period homes

Cellars in older London houses were rarely built to be lived in. Solid brick walls, lime mortars, no damp-proof course and high moisture levels are normal. Turning a cellar into usable space means choosing a system that works with that construction rather than against it — often a cavity drain membrane, which tolerates some movement and moisture in the background. In listed buildings, the choice of system and fixings may need listed building consent, and we can work with your conservation officer or architect on a sympathetic approach.

North, south and west London

Our basement tanking work covers London-wide projects, including:

• West London — Kensington, Chelsea, Notting Hill, Holland Park and Fulham, where lower-ground floors and vault conversions are common.
• North London — Hampstead, St John's Wood and Marylebone, with large period houses and garden-level conversions.
• Central London — Mayfair, Belgravia, Pimlico and Westminster, including under-pavement vaults.

We also work out across the South East to Buckinghamshire, Hertfordshire, Surrey and Berkshire.

How much does basement tanking cost?

Basement tanking costs depend on the size of the basement, the system (cementitious tanking is usually simpler than a full cavity drain installation), whether a sump and pump are needed, the condition of the existing walls and floor, access, and the finishes required afterwards. We quote after an on-site survey because choosing the wrong system for the conditions is the most common — and most expensive — mistake.

Where we work

• North London: Finchley, Barnet, Highgate, Hampstead, Muswell Hill, Islington, Hackney.
• West London: Kensington, Chelsea, Fulham, Hammersmith, Notting Hill, Ealing.
• South London: Clapham, Balham, Wandsworth.