Basement & cellar waterproofing

Help & Information for Homeowners

Basement & cellar waterproofing

Converting damp basements, cellars and other spaces below ground level into dry rooms can be a cost effective and highly rewarding way of extending a home or utilising space within an existing property. Despite the increasing popularity of basement conversions, there is an inherent extra complexity when considering converting these underground structures.

One of the first considerations should be how will moisture be managed, whether it be preventing the potential for external sources of water entering the basement or how water generated within the structure be discharged. The management of water in below ground structures is often referred to as structural or basement/cellar waterproofing.

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But what exactly is basement waterproofing?

Basement Waterproofing is the term that describes methods used to prevent water entering rooms that are below ground. Basement Waterproofing is needed when a new underground space is created or an existing basement is refurbished to provide a usable or habitable space.

What are the waterproofing options available?

There are three waterproofing systems, Type A, B and C. However in reality, for most basement conversions, you will be limited to certain type A and type C systems. To learn more about the different types of sytems, keep scrolling...

PCA - Type A Waterproofing

Type A waterproofing

Type A, usually referred to as ‘tanked protection,’ is a structure with no integral protection against water penetration. It relies totally on a waterproofing membrane to keep water out. Type A forms of waterproofing may be applied internally or to the outside of the structure or, in some cases, sandwiched between two skins of masonry or concrete.

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PCA - Type B Waterproofing

Type B waterproofing

Type B are structures built with a water-resistant shell, usually constructed out of reinforced concrete to an appropriate design code, which gives guidance in the grade of concrete to be used and spacing of the reinforcing steel. Special additives may also be used.

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Basement & cellar waterproofing - Homeowner Help & Info - PCA

Type C waterproofing

Type C or ‘drained cavity’ systems rely on a drained cavity within the basement structure. There is a permanent reliance on the cavity to collect groundwater that enters through the fabric of the structure. The drainage system directs the water to a drain or sump, where it can be removed from the building by gravity or pumping.

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Some key questions for a successful basement or cellar conversion

Although hidden away, basement & cellar waterproofing can be particularly sensitive to failures, largely due to poor workmanship, the inappropriate use of materials or bad design. As a result, a range of factors need to be carefully considered when undertaking such works, to ensure a positive outcome. Below are some questions to consider...

+ Q: Will I need planning permission?

In most cases, planning permission is unlikely to be needed when converting an existing basement or cellar. However before progressing with a basement conversion, you should check with your local authority whether planning permission is required.

+ Q: What are the standards when it comes to basement waterproofing?

Basements are one of the most critical areas of construction and conversions and, as such, must comply with BS8102 2022. In addition, all PCA structural/basement waterproofing contractor members are expected to to follow all PCA 'Codes of Practice for waterproofing below ground structures' and 'Best Practice Guidance' towards the installation of any waterproofing systems.

+ Q: Who can I trust to carry out these works?

PCA members within the waterproofing sector have the necessary expertise to ensure their project is a success, with experience in this complex, highly skilled aspect of construction. The Association oversees the industry recognised qualification, Certificated Surveyor in Structural Waterproofing (CSSW), attained by professionals in the sector.

10 steps to successful waterproofing

10 point overview on achieving successful structural waterproofing projects by providing an overview of some of the main areas to consider to keep projects on the right track

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Tanking walls

What exactly does ‘tanking walls’ mean and is it different to waterproofing?

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If the waterproofing fails in my basement/cellar

Unfortunately failures in basement waterproofing resulting from inadequate specifications or poor workmanship are usually very costly to put right. Waterproofing below ground is a highly specialised operation and must be undertaken by contractors and designers who have the requisite levels of skill, understanding and experience.

Where can I find reliable experienced contractors?

The PCA can signpost homeowners to members with the necessary expertise to ensure their project is a success, with expertise in this complex, highly skilled aspect of construction.
The Association oversees the industry recognised qualification, Certificated Surveyor in Structural Waterproofing (CSSW), attained by professionals in the sector.

The PCA also has a register of Waterproofing Design Specialists who have signed-up to annual CPD and able to provide standalone design services, who along with a geotechnical specialist, make up the core components of a waterproofing design team.

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Why use a PCA Member - Experts in their Sectors

Structural waterproofing guidance for construction & property specialists

For professional tradesmen or contractors looking to find out more technical detail about Structural Waterproofing, visit our professional guidance section.

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More about the PCA

Learn more about the PCA, what we do, our values and why our members and contractors see the PCA logo as a 'badge of honour'.

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Basement & cellar waterproofing