Estate agents are urging homeowners to restrict home improvements to a paint job or a garden makeover rather than building a new kitchen, as costly extensions could leave them up to £20,000 worse off. As house prices slump there is no longer any guarantee that costly renovations will result in a corresponding increase in a property's value, according to research from a high street lender. They found that almost a third of estate agents have changed their advice in the past 12 months when it comes to home improvements.