We have a case of requiring to extend the damp proof up about 9 inches after a neighbour lifted the height of their path (happened before we moved in)
its affecting the garage and downstairs cloak room, any suggestions we would prefer not to request the neighbours dig up their path having just moved in.
The garage has a bedroom and shower room above it which is an extension and the RSJ's supporting this stand on additional block columns. Decorating isnt an issue as its a garage and the cloak room looks like a swedish sauna which isnt a style we're going for and so will be redone (we guess the damp issue is why they added the boarding)
As Chris has just stated best and most reliable method is to restore grond level below DPC on the neighbours side otherwise you may be chasing this problem continually ,damp problems have a habit of re surfacing!
One must inject the wall 150mm above the new ground level, waterproof render to at least 300mm above that but 1.2m would be recommended. Your floor may also be affected in time, this cannot be avoided without removing part of the floor!
Best to get the ground level back to normal if you can.