A bathroom or utility room aren't classed as habitable because it's highly
unlikely someone's going to sleep in them, if they did and got killed in a
house fire then tough titty.
Bedrooms, living rooms etc are habitable and covered by fire regs,
especially where a third floor is occupied (loft)

Brian Gaff wrote:
I guess it depends on your definition of habitable. If you are
continually going there to put stuff up in the loft or bring it down
then to my mind its habitable. If you are not going to use it much
then why clutter the place with a permanent staircase all the time?
Brian