72 per cent of the nation’s basement developments are believed to be undertaken in London, with nowhere else suffering from the same shortage of space and inflated land prices.

If you believe the newspapers, you could think these developments are all extravagant playthings for those with money to burn; in fact, most are commissioned by people desperate for more space for perfectly good reasons, such as growing families or expanding businesses, and they are anxious to get as many square feet as they can for the available funds.

This is why many are tempted to cut corners

The National House Building Council has voiced alarm about the escalating number of tanking defects and other major construction faults coming to light after builders have left and large sums have been expended on interior decoration and furnishings. There have been nearly 1,000 significant litigations in the past ten years, resulting in awards totalling several million pounds each year and much more to put everything right.

Approximately two-thirds of all claims relate to the ingress of damp. About one-quarter of failed builds had attempted inappropriate damp control strategies from the start, while the other three-quarters broke down due to smaller errors in applying membranes or in the sealing methods used around pipes and other penetrating services.

Compromised safety

The concern about incompetent construction standards comes on top of other bad news about incompetent safety standards. Large numbers of property owners do not commission an experienced specialist London basement company, instead using ordinary builders or led on by entrepreneurial tradesmen of sundry kinds. They in turn often hire the cheapest labour, many of whom are inexperienced migrants. After extensive investigation of sites across the city, the Health and Safety Executive recently determined that the proportion of basement construction sites without appropriate safety measures in place is well over one-third, which is an appalling figure.

There have been a number of deaths and several well-publicised building collapses. A typical example occurred in Finchley after Edward Goldswain and his eight-months pregnant partner Jacqueline Hale hired a plumbing firm to extend the basement beneath their ground floor flat. Cracks in the wall went from 1cm to 10cm wide in under 20 seconds before a wall of the house collapsed entirely, leaving the family homeless and with a 23-year mortgage on a derelict building. They were also left facing litigation from the neighbours, while the plumber simply declared bankruptcy.

A judge concluded that the company was simply unqualified to undertake this kind of work. The majority of faulty and bodged basement constructions are the work of companies that are not specialists in basement builds and inadequately appreciate the unique challenges they present. Most are either ordinary general builders or teams assembled ad hoc by opportunist tradespeople hoping to get on board the basement construction bandwagon.

Choosing a specialist London basement company rather than a general builder is not just a matter of safety. Saving a few pounds for a lower quote is false economy when you consider the very high costs of rectifying basement construction mistakes afterwards.