Third floor - rules for second means of escape

[SJRSJR]

Hello.  I have a two story house plus a loft conversion which is currently only accessible via an external metal staircase.  I’d like to have an internal staircase installed from the first floor up.  

As I understand it, with a third floor, all doors on the first and ground floor which lead to the exit (front door) need to be fire rated. 

Does that apply even though there is already a means of escape from the top floor?

All the doors are Edwardian panelled doors and the prospect of them needing new hinges, intumescent strips and fire retardant paint is putting me off.

Thanks for any advice.

[AnthonyB]

The guide doesn't address your layout as it assumes protection of the stair rather than the greater expense of an external stair unless you are a storey higher than you are. You could argue to Building Control that the stair is over and above the requirements and would compensate for an unprotected stair as the upper floor isn't relying on it for safe escape, after all Approved Document B isn't law & if you can show an alternative approach provides equal safety they are meant to accept it- they an only say no