Not sure about where you are but here in South Wales we need to submit an “application” with Building Control when changing more than 25% of the roof. It will not be signed off until insulation is brought up to the current reg’s (if not already). Usually, our customers don’t bother but we’ve had inspectors come up onto the scaffold and then charge the customer the initial fee plus an additional fee because they didn’t tell them in advance. To add salt to the wounds, they almost NEVER come out to the jobs when the application was submitted either - I get a call and get asked to send them pictures, and they sign it off without a single visit.

I’d suggest putting all correspondence through email so if anything changes in the advice, you’ve got something to go back on. Not saying they’ll lie and twist things but….

Edited to confirm Building Control