Understanding Cavity Membrane Systems and Their Functionality

Understanding Cavity Membrane Systems and Their Functionality

3rd July, 2025

Basements and cellars are the most likely part of your London home to suffer from dampness issues, it’s easy for water to naturally seep into them, causing moisture damage and preventing you from using your subterranean spaces in the manner you may wish to. Suppose you want to convert your basement or cellar into a living area or use it for hobbies or storage. You are most certainly going to have to install some damp proofing or see your conversion efforts spoilt by water damage. Fortunately, there is a solution to this problem in the form of cavity membrane systems.

Cavity membrane systems are specially designed to damp-proof underground areas by letting water pass through the internal walls at the membrane’s back. The membrane is fashioned from high-density Polyethylene that is installed on the surfaces of the basement or cellar, including the floors, walls, and even the ceiling! Some designs may include a drainage channel to remove water from the foundations to a sump pump that will carry it outside and away from your cellar.

The cavity membrane system falls under the category of Type C waterproofing, meaning it is meant to provide a structure with drained protection. Cavity membrane systems are the best available method for damp-proofing basements and cellars in an existing home, and are also popular for use in new construction. A basement or cellar’s external earth-retaining walls must be able to withstand hydrostatic pressure caused by the build-up of external water against the walls. The external walls can provide a certain amount of pressure resistance but if there are any weak spots then water might be able to seep through them, causing issues with dampness and even flooding, resulting in untold damage.

The cavity membrane system is installed to ensure that below-ground structures remain safe from the problems caused by water ingress. The system channels and redirects moisture that is able to enter through the outer walls and drains it harmlessly away to a safe runoff. The system creates a barrier that stops water from getting through the inner walls so it can never reach valuable items in the cellar or basement.

Cavity membrane systems can be used for both refurbishment projects in older homes and new builds. They need to have accessible drainage set up for them to be effective. This is often accomplished using a modular drainage system. Some prep work will be necessary before the membrane can be installed including treating new concrete, brickwork, or stonework with an anti-lime substance intended to prevent the formation of limescale inside the new drainage system.

Cavity membrane damp proofing systems are the most reliable option available, you can expect them to last for decades so your cellar and basement spaces will be well protected from the damp and stay nice and dry.

If you have damp issues in your cellar or basement, ring us at London Damp Surveys on 0207 305 5997 and we’ll send an expert surveyor to assess the project.