Loft conversion with open plan ground floor but first floor escape

[dekesta]

Hi, I know this has been discussed a lot but I’m looking to convert a second floor loft space into habitable rooms and I have an open plan ground floor. I don’t want to partition the ground floor and don’t want sprinklers so I was looking at using a first floor external door leading to a flat roof with external staircase. The building control officer said that’s fine but I would need to separate the ground and first floors - does this sound right? I’ve not seen this documented for a domestic 3 story house??