NHBC Standard 5.4 Basement Waterproofing

NHBC started a basement campaign in 2013 to highlight the issues, with this including the publication of a new basement standard – ‘5.4 Waterproofing of Basements and Other Below Ground Structures’, released in December 2014.

NHBC are promoting an approach to waterproofing design and installation which falls broadly into line with the guidance detailed within British Standard 8102 (2022) Code of practice for the protection of below ground structures against water ingress, which advises design by specialist waterproofing designers, and specifications driven by an assessment of risk, primarily relating to site conditions and structure – could not agree more.

To NHBC’s credit however, they have pushed even further with specific requirements which will greatly assist in reducing problem basement waterproofing systems.

Firstly they state that installation should be by trained, qualified operatives.  This will address the historic situation where tanking products were sold through building merchants, with general contractors/ground workers picking these up and then using untrained labour to install.

Another example relates to the use of ‘combined protection’, which is a section within BS8102, advising that where site conditions are aggressive (very wet) or the consequences of failure are dire – (generally the case within habitable basements representing the majority of NHBC’s insured property) – that two forms of waterproofing system be employed to provide suitably low risk levels.