@Jammy5 i know it's not what you asked but have you considered a fire suppression system? our architect designed our house without one with large opening windows from every room upstairs and things to protect stairwells to multiple exit routes from the basement etc. in the end it probably cost us more than a fire suppression system would have!
in hindsight, if our architect had said we can save £X and hassle by installing fire suppression i'd have probably jumped at it.
just wondering that if you installed one of those you wouldn't have to worry so much about the fire rating of some things maybe?