I am working on a wall which may have rising damp, it appears to be so as it
has been treated twice before bthe treatment failed twice within 2-3 years.
nowhere else is damp in the house.

The wall is in a one storey extension at the side of the kitchen. the sign
of damp is on the internal wall only but not on the external one. what
tests can I do to determine whether this is really rising damp rather than
condensation (kitchen is hot, extended area is always cold and the outside
wall is north-northwest facing.

Also, what steps can i make eliminate damp (if it is that) or condensation.
Would vents and heating help? - there is neither at the moment.

Thanks
M