Can I renovate a house and sell it?

Yes, you can renovate a house and sell it, and people make money doing it, but the profit is decided on the day you buy, not the day you sell. Work the numbers backwards: end value of the finished house, minus purchase price, renovation cost, buying and selling fees, finance and tax. If what is left does not survive a 10 per cent overrun, walk away. We have priced up auction purchases in Lewisham for buyers who did exactly that, and they were glad of it.

The work that reliably adds value in our patch is not exotic. An extra bathroom, a reworked kitchen, a loft bedroom. A dormer loft conversion starts from £50,000 and on most South East London streets adds comfortably more than that to a three-bed terrace. Kitchen extensions run from £2,500 per square metre. Cosmetic refurbishments of tired ex-rentals are the classic flip, because the spend is mostly decorating and bathrooms rather than steel.

Two warnings from jobs we have watched go wrong. Do not renovate to your own taste; developers fit neutral, hard-wearing finishes because buyers pay for space and condition, not personality. And keep every certificate: electrical, gas, building control completion. Buyers' solicitors ask for all of it, and a missing completion certificate can knock more off your sale price than the works cost.

If the sums look tight, get a builder to walk the property with you before you exchange. We do this regularly. A survey first, then a fixed written quote, turns your biggest unknown into a line you can actually plan around.