We are currently under offer on selling our house ( yes it does happen) and the buyer had a gas heating engineer in doing a survey yesterday. He went into the roof and commented to the buyer that the roof joists did not meet the current specification. He claimed they need to be 6 inches deep whereas ours are 4 inches. About 10 years ago when I bought the house we had a structural survey done and the report did not highlight a problem with the roof joists but possibly regulations have changed since then.
is there a simple answer to the question: how thick do roof joists need to be or does it depend on other factors?
Any help you can give would be gratefully received.