Cavity Drained Protection (Type C Waterproofing Systems)

A ‘Type C’ Waterproofing System is a maintainable waterproofing solution for new-build basements, refurbishment and retrofit projects. The Type C System comprises of two key components, a Cavity Drainage Membrane and Basement Drainage system.

BS 8102:2022 (Protection of Below Ground Structures Against Water Ingress – Code of Practice) defines Type C waterproofing as a protection system that manages water that penetrates the external shell of a structure, by collecting this water ingress in a cavity formed between the external wall and an internal lining/wall.

Benefits of a Cavity Drain System

In principle a cavity drainage system allows moisture or running water to travel behind the installed membrane system as a controlled drainage system.  A cavity drain system requires minimal preparation and disturbance to an existing substrate.

Waterproofing Design Service

A Waterproofing Design Specialist provides expertise in structural waterproofing.

A Waterproofing Design Specialist should be appointed as part of the design team at the planning stage or as early as possible so that an integrated waterproofing solution is created.   All decision made by others that might have impact on the waterproofing deign should be brought to the attention of the Waterproofing Specialist, Design Team, and Installing Contractors.  Final decisions and any recommendations should be approved by those taking overall responsibility for the design of the waterproofing.

Identifying a Waterproofing Design Specialist can be difficult and daunting, Delta has their own in-house Technical Team who are able to offer Waterproofing Design Services.  Our Waterproofing Design Consultants have:

  • Suitable qualifications and experience in Structural Waterproofing
  • Be able to list the principal considerations for a robust waterproofing design
  • Offer knowledge on waterproofing systems available
  • An in-depth understanding of BS 8102:2022 and its requirements
  • Be able to assess risk and reducing risk in suitable waterproofing designs
  • Desk top study & risk assessment knowledge – these should form part of any Designers Report and Waterproofing Design
  • An understanding of sources of water (such as how it flows through the soil and interacts with the structures)
  • Have knowledge on all Types of waterproofing systems, their suitability to the project/an understanding of limitations on drainage options
  • Structural knowledge
  • Knowledge of Ground Gases
  • Geotechnical knowledge (to be able to understand the implications of a soil report)
  • The ability to produce a Design Report, Method Statements and Waterproof Design drawings
  • The ability to provide guidance that assists with and influences future maintenance of the waterproofed structure.

Internal Cavity Drain Membranes

Our internal membranes are used as a Type C Waterproofing System forming a waterproof barrier as well as adequately draining the water to a suitable outlet, in most cases a sump pump drainage system.

Before a cavity drain membrane is laid or fitted on walls and floors constructed of new concrete, the concrete surface should be treated to reduce the risk of leaching of free lime and/or mineral salts and to avoid the obstruction of the drainage system. This can be achieved by using our Polysil TG 500 anti-lime treatment.

Maintainable Designs

Delta’s Type C Waterproofing System should be designed and installed as a maintainable water management system.  This is highlighted as a key requirement in BS 8102:2022, all components of the system should be accessible for both inspection and maintenance.

Commissioning and Servicing of Basement Drainage System

Immediately after the installation of the Type C, Cavity Drainage System, drainage channels and sump pumps should be tested.  A requirement in BS 8102:2022 is for pumping devices to be checked, tested, and fully commissioned by a suitably qualified engineer.  Requirements for servicing and maintenance should be incorporated in both the design and upon completion should be included in the Operational and Maintenance Manual.  A first inspection should be carried out on completion of the installation of the Type C system at handover and commissioning. It is recommended a second inspection should be within the first 3 months after installation.

Servicing of sump pump systems should be carried out no less frequently than annually.  We recommend pumps running frequently due to higher water tables, water drainage, or weather conditions should be examined more frequently, we recommend every 6 months.


Delta Membrane Systems Limited offer a 30-year Product Guarantee on membranes, seals, and fixings when a Delta Registered Installer has installed a Delta, Type C Cavity Drainage System.

Flood Testing/Integrity Testing

The integrity of the waterproofing system should be checked and inspected on installation and immediately upon completion.  If there is a delay before final handover or the laying of permanent coverings, a second test is strongly recommended.  Test objectives should be decided upon prior to the method of testing.

Installing a Delta Type C Cavity Drainage System offers complete protection to structures from ground water ingress and contaminates.  Our products comply with British Standard BS 8102:2022 and are BBA Certified.

  • Type C Drainage Protection in accordance with BS 8102:2022
  • BBA Certified
  • Suitable for new, existing, and retrofit projects
  • Ability to easily deal with aggressive ground water conditions
  • “Grade 3” performance level (no dampness or water penetration acceptable, dehumidification required)
  • “Air Gap” Technology
  • A reversible system, which will not create damage to historical or heritage structures
  • Flexibility to cope in structures where movement or vibration issues can be problematic
  • Virgin High Density Polyethylene studded/moulded sheet (HDPE)
  • Easily applied to a variety of substrates
  • An effective barrier to the transmission of salts, liquid water, and water vapour
  • Suitable for Flood Resilience
  • Can be recycled

‘Type C’ Waterproofing – British Standard 8102:2022

British Standard 8102:2022 (BS 8102:2022) ‘Code of practice for protection of below ground structures against water from the ground’ defines ‘Type C’ waterproofing as “drained protection”.  where the structure itself provides primary resistance against water penetration and incorporates a drained cavity system within the basement structure.

Responsible manufacturing

Responsible manufacturing goes beyond traditional notions of green or sustainability.

As a responsible business, Delta provides waterproofing solutions that focus beyond environmental sustainability, we apply our principles to high-quality solutions.  With targeted quality and safety measures at all levels – every day.

Achieving sustainability in manufacturing requires a comprehensive view spanning not just the product and the manufacturing processes, but also the entire supply chain, including product lifespan.

Delta provides life-cycle oriented designs, addressing life-cycle concepts and methods, deterioration and damage evaluation, life-cycle performance indicators, inspection and maintenance procedures all implemented to work in harmony.

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