Service

Cavity Drainage Membrane

The gold standard for habitable London basements. Our Type C cavity drainage systems manage water to a sump and pump — keeping the space reliably dry, whatever the water table.

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Manage the water, don't only block it

A cavity drainage membrane takes a different approach from a barrier system, and it works well. It does not rely on a coating to hold water back under pressure. Instead, it accepts that water will always try to enter, and gives it a controlled path to a drain, sump and pump.

Because the system manages water rather than resisting it, Type C is extremely reliable, even where the water table is high or variable. That is why it is the system of choice for basements that become bedrooms, gyms, cinemas and living space across London.

The membrane also creates a clean, battened surface that is ready to dry-line and decorate. As a result, you get a dry room with a proper finish. For example, you can fit plasterboard, wiring and flooring straight onto the system.

Some projects need more than one layer of protection. In that case we combine Type C with cementitious tanking for extra security. Every job starts with a free survey, a written report and a fixed quotation.

A typical system has three parts. A studded membrane lines the wall and floor, a channel at the floor edge collects the water, and a sump with a pump removes it. Because each part is simple, the system is easy to service.

Type C is the right choice when the ground is wet for much of the year. However, it also suits dry sites that need a high level of safety. If you are unsure, our survey will explain the choice in plain words.

Ideal for

Habitable basement and cellar conversions
Properties with a high or variable water table
Basements where reliability matters most
Combining with tanking for belt-and-braces protection
Below-ground rooms that need a decoratable finish

How a Cavity Drain System Works

Membrane, drainage, sump and pump — engineered to keep water moving away from your room.

Survey & design

We assess water conditions and design a Type C system with the right membrane, drainage layout and pump specification.

Fit the membrane

Dimpled cavity membranes are fixed to walls and floor, creating a controlled void that directs water away from the room.

Drainage, sump & pump

Perimeter drainage channels feed a sump chamber and pump, which discharges collected water safely away from the property.

Finish & commission

Walls are battened and dry-lined ready for decoration, the pump is commissioned and the system is guaranteed.

Type C System

Drained protection to BS 8102.

Free Survey

Written report and fixed quote.

Guaranteed

Membrane, pump and workmanship.

Cavity Drainage FAQs

What is a cavity drainage (Type C) membrane system? +

It's a 'drained protection' waterproofing system. A dimpled plastic membrane is fixed to the basement walls and floor, creating a controlled air gap. Any water that reaches the structure is channelled behind the membrane to a perimeter drain, collected in a sump and pumped away — so the internal space stays dry.

Why choose a cavity drain system over tanking? +

A cavity drainage membrane manages water rather than trying to resist it with a single barrier. That makes it highly reliable under variable or high water tables, and it's the system most often specified for habitable basements in London. It also allows walls to be dry-lined and finished cleanly.

Do you install sump pumps and battery back-up? +

Yes. A cavity drain system relies on a sump and pump to remove collected water. We install high-quality pumps and can add a second pump and battery back-up so the system keeps working during a power cut — important for fully habitable basements.

Does the membrane need maintenance? +

The membrane itself is durable and largely maintenance-free, but the sump and pump should be serviced periodically to keep them working reliably. We'll advise on a simple maintenance schedule when the system is commissioned.