damp proofing

[plasterman2]

hi new to forum so go easy but can any one advise wether or not there is a need to damp proof an internal wall if im going to batten and re-board .

this wall is an ajoining wall to the neihgbours and they have had theres treated on that side so i was a bit wary as i did not want to trap the damp in the middle as the damp might go down stairs. any help much appreciated