Fixing solid wall insulation to one of the inner walls of a garage.

This wall backs one wall of my living room and the insulation is . Styrofoam by Dow Building Solutions. What adhesive should I use? and need I worry about inserting a damp proof membrane? I presume that very little water vapour should be able to pass through the wall as it is plastered and wallpapered so no membrane should be needed. I look forward to your response. All the best, Wyn