Cavity Drain Systems

Because it's not possible to determine the amount of potential water pressure surrounding structures, MacLennan designers always design a cavity drain system from DPC down.

It is a requirement of British Standards that that all waterproofing is maintainable and repairable. The Cavity Drain Membrane system is the only form of waterproofing that is easily and quickly repaired and maintained.

The cavity drain system can work with natural drainage or pumps. MacLennan would normally advise a pump as a back-up to natural drainage unless the drainage can be proven to be effective in all conditions. In flooding situations the pump sizes are calculated to pump out water twice as fast as it floods in. We would install the system to pump the water to your drainage system.

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    - London
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    -Typical Section through sump.
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    - Southampton
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    - Section through Head Of Wall
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The system would be controlled by a separate control panel and the pumps would be fitted with battery back-up so they can continue to work in the event of a power failure.


You should have your drainage inspected and tested to ensure it can cope the water being pumped into it.

In the event of a power failure, the system automatically switches to battery power with no loss of back-up pump performance. When the normal power supply resumes, the converter switches back to the mains-supply and trickle-charges the battery. It all adds up to complete peace of mind. The use of dual pumps allows one pump to drive the drainage system with the second on standby ready to cut in if there is a pump failure. The sump chamber also includes a 9V high-water alarm which is activated if the main pump fails or total power failure prevents the pumps from working.


We would recommend the MacLennan cavity membrane system in preference to cement based, Bitumen, Epoxy systems or waterproof concrete for the benefits being:

  • The complete system would be guaranteed by MacLennan if the system is inspected and serviced annually.
  • The system is installed after the basement is constructed so is unaffected by weather conditions unlike all other systems.
  • The system is the accepted best practice by insurers for any size or construction of basement.
  • The system would be guaranteed by the GPI insurance guarantee so as the work would be guaranteed in the event that Maclennan should cease trading for any reason.
  • The system would be very flexible and would accommodate any movement in the building.
  • The system is very fast track to install and there is no drying period.
  • The system can be plastered to a finish of your choosing and decorated with any products you wish.
  • By installing an internal perimeter drain, sump and pump the system can be installed to deal with free flood water.
  • The MacLennan cavity drain system will conform with BS8102 PCA codes of practice

Get in touch with our technical team today!

Maclennan have been experts in designing, installing and guaranteeing systems for over 30 years.

  • Finishes

    A wide range of finishes can be adopted to walls, floors and soffits, which also provides protection to the membrane system. Typical wall finishes include:

    • Block work wall built in front of the system.
    • Independent timber framing and plasterboard.
    • Independent metal framing systems.
    • Conventional plasters and renders.
    • Tiling and cladding.
    • Floors
    • Sand and cement screeds.
    • Fast drying screeds with lightweight reinforcement.
    • Wood-based sheets (tongue and groove flooring grade).
    • Timber boarding on floor beams.
    • Under floor heating systems.

    All the above finishes can be installed with insulation, where appropriate or specified.

  • PDF Drawings

    cavity drain pdf 1
    cavity drain pdf 2
  • Environment

    Any building work in a basement or below ground area will produce water, which will condensate on cold surfaces for a short period of time during and after the work. The basement heating, ventilation and insulation should be designed to remove excess moisture vapour so the basement has a comfortable environment free from condensation. Environmental control is not a part of the water proofing design or installation and should be designed by a qualified mechanical electrical engineer.

Why should I work with MacLennan?


We Design, supply and install. There's no split responsibility with MacLennan.


MacLennan live and breathe waterproofing, have a look at one of our free CPD seminars and find out!


MacLennan has the most comprehensive guarantees and insurances in the industry.

Safe Contractor Approved
ISO URS 9001
Chas Advanced
Acclaim Health And Safety Approved
Constructionline Gold Member
Achilles Building Confidence
The Radon Council Member
Safe 4 Site Gold Member

Get in touch!

Ready to start a project or require more information about us?
Call us about your project or problem and we will be happy to help.

Call us today on:

0330 3200 240
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