Type C waterproofing · London
Cavity Drain Membrane Installation London
Specialist Type C waterproofing for basements, cellars and below-ground structures. Rather than trying to block moisture, a cavity drain membrane manages and controls it safely, the most reliable approach for many London basements and habitable conversions.
Over 30 Years Experience
Below-ground waterproofing specialists across London.
CSSW Qualified Surveyors
Systems designed and specified to BS 8102:2022.
10-Year Guarantee
Written guarantee on all new waterproofing installations.
CHAS Accredited
Fully insured, fixed-price quotations after survey.
What Is a Cavity Drain Membrane?
A cavity drain membrane is a studded, high-density membrane fixed to the walls and floors of a below-ground space, creating a controlled cavity behind the internal linings. It is the Type C, or drained protection, system defined in BS 8102:2022. Instead of resisting water, it manages it.
Managed
Any moisture entering the structure is collected in the cavity behind the membrane, away from your finishes.
Channelled
Water is directed into perimeter drainage channels around the floor edge.
Discharged
It is taken to a discharge point, a gravity drain or a sump and pump where required.
Why Type C Works Best in London
Many London properties have basements that were never designed as dry living spaces, and the city's clay-heavy ground creates sustained pressure against them. A drained system copes with that pressure far better than a barrier alone. London basements commonly face:
When Is a Cavity Drain Membrane the Right Choice?
Type C systems are often ideal for the following situations. A professional survey confirms the correct specification for your property.
What We Install
Wall Membranes
Fixed securely to create a managed cavity behind the internal finishes.
Floor Membranes
Installed beneath the floor build-up to protect against moisture rising through the slab.
Perimeter Drainage
Channels that collect water and direct it to a discharge point.
Sump & Pump Systems
Where a basement cannot discharge naturally by gravity, with battery backup where needed.
Vapour & Ventilation
Moisture and humidity control to keep the finished space comfortable long term.
Newton Systems
As approved installers of Newton Waterproofing Systems, we fit fully maintainable, proven products.
Cavity Drain Membrane vs Tanking (Type A)
Clients often ask whether tanking or a membrane is better. The correct choice depends on the building, the water risk and the intended use of the space.
Type A · Tanking
- Works by resisting water penetration
- Effective in sound, lower-risk structures
- Higher risk if movement occurs or pressure is high
- Suited to storage cellars and barrier applications
Type C · Cavity Drain
- Manages water safely rather than fighting it
- Often preferred for habitable conversions
- Maintainable drainage for long-term performance
- More reliable under London's hydrostatic pressure
Compare with basement tanking and cellar tanking, or read our overview of below-ground waterproofing systems.
Cost & Remedial Installations
Cost depends on the size of the basement, the ground conditions and whether a sump and pump are needed. We always survey and provide a fixed-price quote before any work is agreed.
The survey fee is deducted from the cost of works if you proceed.
We also install cavity drain systems as a remedial fix where historic tanking has failed, where internal plaster has been contaminated by salts, where previous works were incorrectly specified, or where water ingress continues despite repeated treatment. A structured Type C approach prevents recurring failure and protects your investment in the space.
Why Choose Advanced Damp
A Real London Type C Project
Case Study · Kvadrat Ltd, Shepherdess Walk, London
Commercial Type C waterproofing for a London below-ground space
We designed and installed a commercial cavity drain membrane system for Kvadrat at their London premises, managing water ingress to create a dry, usable below-ground area. The system was specified to BS 8102:2022 and handed over with our written 10-year guarantee, a clear example of the same Type C approach we bring to basements and cellars across London.
Read the full case study →
Approved Installer of Newton Waterproofing SystemsFully maintainable, proven Type C cavity drain products
Accredited & Trusted
Is Your Basement at Risk?
Take the free 60-second check to see how much water risk your below-ground space carries and what the right next step is. You get your result instantly, no details required.
Cavity Drain Membrane FAQs
What is a cavity drain membrane?
A cavity drain membrane is a studded, high-density membrane fixed to the walls and floors of a below-ground space, creating a controlled cavity behind the internal linings. It is the Type C system in BS 8102:2022, managing water and channelling it to drainage rather than trying to block it.
How does a Type C cavity drain system work?
Rather than resisting water, it manages it. Any moisture entering the structure is collected behind the membrane, channelled into perimeter drainage, and taken to a discharge point, either a gravity drain or a sump and pump. This keeps the water away from your finished surfaces.
Is a cavity drain membrane better than tanking?
It depends on the property. A cavity drain membrane (Type C) manages water and is usually more reliable where pressure is high or the basement will be habitable. Tanking (Type A) resists water and suits sound, lower-risk structures. A survey establishes which is right for your building.
Does a cavity drain system need a pump?
Only where the collected water cannot discharge naturally by gravity. Many London basements do need a sump and pump, often with a battery backup. We design the system so the pump and drainage remain accessible and maintainable.
How long does a cavity drain membrane last, and is it guaranteed?
A correctly designed and installed Type C system can last for decades, and because the drainage is maintainable it can be serviced over time. New installations carried out by our team carry a written 10-year guarantee.
Can a cavity drain system be installed where tanking has failed?
Yes. Installing a Type C system is a common and reliable way to resolve failed tanking. We investigate the cause of the failure, remove or work around the defective system, and install a maintainable cavity drain membrane to stop the problem recurring.
How much does a cavity drain membrane system cost?
For a habitable London basement, a Type C cavity drain system with drainage and a sump pump typically costs between 6,500 and 12,000 pounds plus VAT, depending on size and ground conditions. We provide a fixed-price quote after a survey, with the survey fee deducted from the works.
Does a cavity drain system need maintenance?
Maintenance is minimal but important. The sump, pump and drainage channels should remain accessible and be checked periodically to keep the system working reliably. We design every installation with maintainability in mind.
Related Services
Get Your Basement Surveyed
Book a survey and our CSSW qualified surveyors will assess the structure and water risk, then specify the right Type C system to BS 8102:2022 with a fixed price. The survey fee is deducted from the cost of works if you proceed.