If in doubt, get a second opinion from your own surveyor.
And a warning to second owners of new houses: don’t be lulled into a false sense of security by the ten-year guarantee you inherit from the previous owners.
A condition of the guarantee is that faults are reported as soon as possible. If the previous owner failed to do this – as well he might have, knowing he was moving anyway – you could find yourself bankrupted by out-of-guarantee repairs. The solution is to have a survey done before buying.
Building extensions and repairs
The NHBC won’t guarantee or inspect any building work besides new homes so you must exercise a fox-like caution. Find a good builder, and get a solicitor to draw up a contract. With what any building work is going to cost you these days, you would be wise to invest in a final survey, too.