Between 2005 and 2013, claims related to waterproofing below ground cost the National House Building Council (NHBC) in the region of £21 million and affected around 890 homes. As a result, back in 2013 NHBC launched a Basement Campaign highlighting significant issues with the design and construction of basements.
A New Chapter For Below Ground Structures
A key recent development of the campaign has been the introduction of Chapter 5.4 ‘Waterproofing of basements and other below ground structures’.
The new Chapter introduces meaningful benchmarks and supporting technical guidance for a range of situations where the structure is required to resist the ingress of water from the ground and other sources, where ‘normal’ waterproofing arrangements are not considered appropriate.
“In order to help facilitate these changes, the new Chapter will become effective only when included in the re-launch of NHBC Standards, due to be published in 2015. However, while the Chapter will not become effective immediately, it is strongly recommended that the guidance is adopted at the earliest opportunity” – Mark Jones, Head of House-Building Standards, NHBC
The Chapter is essential reading for technical and construction directors and managers, architects, designers and site managers.
Basements Are Not The Only Below Ground Constructions Which Need Waterproofing
The Chapter explains that the range of structures that require waterproofing goes significantly beyond what readers might typically consider as ‘basements’. Below ground constructions that generally require waterproofing, and should take account of the new Chapter, include:
- Semi basements
- Below ground parking areas
- Lift pits
- Storage or plant rooms
- Service ducts or similar that are connected to the below ground structure
- Stepped floor slabs where the step is greater than 150mm.
Near to ground constructions that may require waterproofing include:
- External walls where the lowest finished floor level is less than 150mm higher than the external ground level.