The alterations and extensions made to people's homes have added billions of pounds to property prices across Britain.
Over the last 12 months, the work has added a combined £6.5bn to the value of homes, as nearly a quarter of a million owners made changes, adding around £30,000 per property on average.
In London, where homeowners have increasingly been forced to dig downwards to extend by building basement extensions, that falls to one in 44 homeowners.
The capital and the south east made up the lion's share of the value which has been added, accounting for around £3.6bn, according to research by estate agent Savills.
“The cost of taking the next step up the housing ladder and the difficulties in acquiring the mortgage finance to do so appear to have encouraged a significant proportion of owner occupiers to extend or alter their existing home," said Savills head of residential research Lucian Cook.
"Changes made by the mortgage market review and increased stamp duty for properties over £1m are both likely catalysts to home improvements, impeding the rate and volume of transactions in the market.”