The National House-Building Council (NHBC) has announced details of its new Standards Chapter to improve the quality and build of basements.

Last year, NHBC revealed that between 2005 and 2013, waterproofing below ground structures cost the industry £21m, 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.

NHBC’s Mark Jones, head of housebuilding standards, said: “The new Chapter introduces significant changes in the way the housebuilding 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 – This should be undertaken by a suitably qualified specialist and be appropriate to the level of risk. If waterproofing part of the structure forming a space where ‘Grade 3’ protection is required 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.