I admit to not a lot of knowledge on this subject, but who has told you that you have rising damp? According to various online sources,
rising damp is uncommon, and damp is more likely to be
condensation (bad airflow for example) or penetrating damp (due perhaps to a breached wall cavity, or a roof leak). Personally I would only trust a survey by someone who is independent i.e. does not work for a company that provides damp proofing services.
Also, how do the walls register dampness? Do you have obvious signs e.g mould, rot, damp?