When converting an existing roof space into a room or rooms the provisions for escape need to be considered throughout the full extent of the escape route. This often means that additional fire protection will be necessary in the existing parts of the house.
For example, a typical loft conversion to a two-storey house will result in the need to provide new fire-resisting doors and sometimes partitions to protect the stairway. This is because it is too dangerous to escape via windows from floors above first floor level.
Mains powered, interlinked smoke alarms will also need to be provided within the stairway at each level.
It may also be necessary to upgrade the fire protection to some parts of the structure of the house such as the floors.
You may also wish to consult 'Approved Document B (Fire safety) - Volume 1: Dwellinghouses'.