The recommended min is 1200mm OR 200 mm above the dampest point , but everyone seems to have this misconception that its a 1mtr and job done , wrong, so if your picking readings up above 1200mm then it opens up other questions , is it rising damp or penetrating , or as mentioned even condensation there are so many factors and questions that need to be eliminated before the rising damp scenario is raised , ie bad pointing and spalled brickwork,cracked renders, bushes and trees up against the wall, sealant around windows and doors etc etc etc
too in depth to go into in proper detail, but what i would say is if you plan on doing this type of work do a course with a reputable company and get the backing of the company using their insurance backed schemes and recognition,