NHBC, the leading warranty and insurance provider for new homes in the UK, has announced details of its new Standards Chapter to improve the quality and build of basements as they become an increasingly common property feature.
Last year NHBC revealed that between 2005 and 2013, waterproofing below ground structure claims cost the industry £21million, affecting almost 900 homes. NHBC Chapter 5.4 ‘Waterproofing of basements and other below ground structures’ is aimed at improving the construction quality and robustness of below ground waterproofing, resulting in reduced need for remedial works, costs and disruption to homeowners.
With increasing house prices and limited availability of land more developers are extending below ground, particularly in London. Recent headlines have included “Why Londoners are digging deep” and basement planning applications have surged in areas such as the Royal Borough of Kensington and Chelsea from just 13 in 2001 to 307 two years ago.
NHBC’s Mark Jones, Head of House-Building Standards, said:
“The new Chapter introduces significant changes in the way the house-building industry considers below ground waterproofing, including an up-skilling of designers and installers and changes to future designs. We worked closely with the industry, including The Property Care Association, to ensure we delivered a comprehensive chapter that will serve the sector for many years to come.”
Chapter 5.4, which will become effective when it is included in the new NHBC Standards, due next summer, covers key issues including;
- Basement design; which should be undertaken by a suitably qualified specialist and be appropriate to the level of risk. If waterproofing is to a part of the structure forming a space where ‘Grade 3’ protection is required (i.e. habitable accommodation) and more than 600mm of ground is being retained, a combined system comprising two types of waterproofing should be used. Where the waterproofing is to more than 15% of the perimeter of the building or more than 600mm high, an appropriate investigation of the ground conditions should be undertaken.
- Materials; only systems, including important ancillary components, which have been assessed and proven to provide suitable performance in a given situation, should be used.
Sitework; Recognising the importance of ensuring correct installation in accordance with the manufacturer’s recommendations, waterproofing should only be undertaken by operatives who are suitably trained or qualified using proprietary components to form complex changes in direction of the waterproofing and service penetrations.
For further information please see NHBC Technical Extra 16, available at http://www.nhbc.co.uk/Builders/ProductsandServices/TechnicalExtra/.