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There continues to be debate over the use of XPS insulation as the spacer within Type C cavity drain waterproofing systems (CDM) where drainage channels are placed above the raft/slab of the basement.
In Newton’s expert technical opinion, if a contractor, specifier, developer or homeowner is looking for a Type C waterproofing system that is, at the very least, maintainable, compliant with the British Standard, and can be underwritten by an insurer, then drainage channels are an absolute necessity.
In the full technical paper available here, Newton introduces the concept behind drainage channels, reviews the dangers of non-maintainable systems, and explains the practical and scientific reasons that support the maintainable drainage channel method.
Including the design and safety advantages that have become apparent since their introduction, and the reduced incidence of failures of cavity drain membrane systems.
The Dangers of Non-Maintainable Systems
Where the floor membrane is used to drain water to the sump without drainage channels, over time this non-maintainable system can lead to a build-up of limescale, blocking the membrane void and leading to complete system failure.
Type C Systems with Maintainable Drainage
Overall, the benefits of installing drainage channels whilst using insulation as the spacer are numerous and wide-ranging, from design simplicity and financial and environmental savings to the ease of buildability and energy efficiency improvements.
These benefits reach every member of the construction team, including the architect, the installer, and the client, and also mean that a maintainable drainage system is, in our minds, an absolute necessity in Type C waterproofing.
For comprehensive protection in line with BS 8102:2022, combining Type A protection externally, Type B protection integrally, and Type C protection internally with closed-cell XPS insulation and drainage channels will give the greatest chance of success.
Our staff are able to provide guidance for projects of all sizes, whether you require some general advice about damp or waterproofing, or support with technical drawings and specifications.