The first thing to remember is that in a listed building, particularly of
that age, there is very little that can be legally done without getting
formal listed building consent from your local planning authority. Indeed is
a criminal offence to make many changes without such approval.
Unfortunately it means your will have to wade through a lot of bureaucracy.
You need to choose a structural engineer or surveyor who specialises in such
buildings. It does not come cheap and the figure quoted by someone else is
absurd.

Peter Crosland