Hi - I'm looking for a spot of advice:

I own a terraced house, that was built in 1847. There is a stud wall
between the stairs and the kitchen. Recently, I noticed that there was
a "tide mark" along the bottom of the kitchen side of the wall that
looked as though it might be damp. The other side of the stud wall is
the understairs cupboard, so I have removed the plaster board to
investigate the problem.

My investigations have revealed the studs in the wall to be extreemly
rotten, and they don't appear to be on any solid foundation. I am
concerned becasue I suspect that at least one of these studs is
providing support for the ends of some of the joists, as the stairs
prevent them crossing fully between the two party walls.

Does anybody have suggestions on what the best course of action would
be?

Thanks,
And.