And if it is a 1960s extension run a bloody mile! Well, probably not fair - there are probably loads of good 1960's extensions. Ours however was shocking. We have had to practically re-build it....wooden fence posts used as lintels across 2m wide windows, 4 inch joists, duff electrics. The works. shudders. So anyway - if is an older property/extension not covered by building regs etc then get a bloody good survey.