Basements are a growing cause of concern for the UK housing industry with just 14 claims over £50,000 costing nearly £3million in the last year alone, new figures by NHBC have revealed.
Claims on basements built since 2005 have cost the industry a total of nearly £21million – affecting nearly 890 homes. Changing weather patterns, a growth in the popularity of basements and a push for more sustainable urban drainage mean that basements present an ongoing risk which needs to be effectively managed.
NHBC figures show that large loss claims – those costing over £250,000 – have risen from £400,000 in 2010 to £1.5million in 2011 and £1.7million in 2012. When combined with other smaller claims, the total costs have risen from around £3million in both 2010 and 2011 to £4.8million in 2012. These figures are expected to rise further as some claims are still ongoing.
The vast majority of new basements (72 per cent) are registered in London with 93 per cent registered in England.
As the UK’s leading insurance and warranty provider for new homes, NHBC has undertaken two recent surveys of around 1700 sites which highlighted key problems surrounding the construction of basements.
The research found that tanking defects were the main cause of claims – accounting for 66 per cent of volume and 62 per cent of basement claims since 2006. These related mainly to the detailing of joints at ground level, floor level finishes and openings for services, pipes and cables.
NHBC found that over a quarter (28 per cent) sites surveyed reported high or unknown water tables, but still proposed a Type A (tanked) or Type B (Water resisting concrete) which may not be suitable for the site. The majority of the large claims from 2012 were as a result of water ingress and incorrect installation of the damp proof membrane.
NHBC is now looking to revise its standards and guidance on basements working closely with the industry to help improve basement design and construction.
It has advised the housing industry to carry out suitable desk studies and ground investigation reports before construction as water levels are critical to the structural design of basements. The surveys also highlighted the importance of adopting the correct waterproofing system and water stops to provide enhanced resistance in joints.
Mark Jones, NHBC’s Group Head of House-Building Standards, said:
“In recent times, we have seen basements once again become a relevant and attractive addition to many houses, But as our claims figures and experience show, basement claims by their very nature are difficult to investigate and costly to repair, which can result in significant disruption to homeowners.
“This new guidance, as a result of surveying hundreds of live sites, will hopefully inform the industry and help reduce the risk for homeowners having to endure problematic basements and inconvenience – at a significant financial cost to the sector.”
Technical Extra is available online at www.nhbc.co.uk/Builders/ProductsandServices/TechnicalExtra