An apparatus for providing an interstitial space to the surface of wall, the apparatus comprises: an adhesive layer; a layer of fluid impervious and weather proof material in form of a tape, the tape partially overlapping itself; a layer of spacer material situated between the surface of the tape facing the wall and the surface of the adhesive layer distal from the wall. The spacer material has ends which are encapsulated, the apparatus providing a sealed interstitial space.