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https://www.firesafe.org.uk/domestic-property/

Perhaps barn conversions fall through a loophole?

Whatever do you mean 

My understandings.

It is not totally clear from your wording whether you are the owner/occupier, or you are the owner and it is rented out on a lease or as holiday let, or you are the occupier renting from someone else. Diffrent scenarios. different laws. If you are the owner/occupier it is your perogative if you want to put your own family at risk. In other cases, the owner of the property assumes responsibility and is subject to additional legislation.

I'm guessing you haven't had windows fitted to an upper floor?

Don't be silly. Up to and including Velux in roofs. Fully escapability.