Hello, recent loft converter here - ours was done this summer.
We didn’t have a dormer so no need for specific planning on that but we did pay the council fee for inspections and reg approval so we could get a signed off certificate at the end of the build. This was around £900, and the builders then liaised with the council.
the fire regs are really really important here. Every single door in the house that is deemed to be part of the fire escape route needs to be a fire door. Our doors look like normal doors, but they are deemed fire resistant as they are thicker and heavier. (Just look on the Howdens website). Also, we had to have every ceiling on the first floor reinforced with fire board. This gives an extra half an hour in the case of a fire for escape from the top floor. It was an absolute ball ache as it meant every room was impacted with dust and plastering and redecorating. Also, the new staircase had to be fire resistant too.
the inspector came sporadically during the build, plus the builders took numerous pics to document they were doing it properly.
we also have smoke alarms everywhere- these are electronically operated rather than battery, and I’m gobsmacked the vendors don’t have any alarms.
if you love the house, as an absolute minimum try and find a good, reputable builder to come and look at the conversion and tell you what needs to happen to either make it so it passes regs, or what can be done to make it safer to help escape in case of a fire.
what did the current vendors ask / do when they bought the house?