When a London property developer purchased a £2M-plus St John's Wood house at auction only to find it was suffering from subsidence before he had the chance to insure it, he decided to transform the negative into a positive and turn the underpinning job into a basement conversion.
The owner already knew a substantial amount of underpinning was necessary to stabilise the property because of the prevalence of clay subsoils coupled with an extensive network of tree roots.
The house also had a halfheight cellar so it soon became clear that by underpinning outside of the central area, he could increase the property's footprint by 25%.
Withers Group subsidiary Basements started work in January and expects to complete the £145,000 job in June.
Managing director Rob Withers said: 'The conversion will add an extra 70m 2 of space and the developer is planning to turn this into a basement at. We're using traditional hand-dug underpinning with a precast concrete oor for the basement and waterproong with a Delta Membrane system.' The Delta Membrane high density polyethylene is designed to deal with aggressive ground water conditions, where basements are liable to flooding, or where dampness, contamination or salting problems are prevalent.