Method for laying a sub-roofing sheet on pitched roofs with adjacent roof surfaces, wherein at least one longitudinal edge-side adhesive zone is provided on the underside and on the upper side of the sub-roofing sheet , wherein the underside facing inwards in the laid state and the upper side facing the weather side are of identical construction, wherein the sub-roofing sheet has a watervapor-permeable and diffusion-open functional layer and wherein the sub-roofing sheet is of diffusion-open construction, wherein the sub-roofing membrane has an S d value of less than or equal to 0.5 m, wherein the sub-roofing sheet has an underlayer comprising the underside and an upper layer comprising the upper side , wherein the underlayer is formed symmetrically to the upper layer , wherein the underlayer and the upper layer have a carrier layer , namely an identically formed non-woven layer, wherein the functional layer is formed as a microporous film and/or as a monolithic membrane layer, wherein the underside has at least substantially the same weight per unit area as the upper side , and wherein the weight per unit area of the upper layer formed as a non-woven layer and the underlayer formed as identical to the upper layer is between 40 and 100 g/m 2 , wherein a first sheet row is cut off obliquely at an adjacent roof surface, the cutoff part of the first sheet row forming an adjacent sheet row , the adjacent sheet row being turned over so that the upper side of the first sheet row forms the underside of the adjacent sheet row , the adjacent sheet row being connected indirectly and/or directly to the first sheet row and/or being arranged on the adjacent roof surface. wherein at least one longitudinal edge-side adhesive zone is provided on the underside and on the upper side of the sub-roofing sheet , wherein the underside facing inwards in the laid state and the upper side facing the weather side are of identical construction, wherein the sub-roofing sheet has a watervapor-permeable and diffusion-open functional layer and wherein the sub-roofing sheet is of diffusion-open construction, wherein the sub-roofing membrane has an S d value of less than or equal to 0.5 m, wherein the sub-roofing sheet has an underlayer comprising the underside and an upper layer comprising the upper side , wherein the underlayer is formed symmetrically to the upper layer , wherein the underlayer and the upper layer have a carrier layer , namely an identically formed non-woven layer, wherein the functional layer is formed as a microporous film and/or as a monolithic membrane layer, wherein the underside has at least substantially the same weight per unit area as the upper side , and wherein the weight per unit area of the upper layer formed as a non-woven layer and the underlayer formed as identical to the upper layer is between 40 and 100 g/m 2 , wherein a first sheet row is cut off obliquely at an adjacent roof surface, the cutoff part of the first sheet row forming an adjacent sheet row , the adjacent sheet row being turned over so that the upper side of the first sheet row forms the underside of the adjacent sheet row , the adjacent sheet row being connected indirectly and/or directly to the first sheet row and/or being arranged on the adjacent roof surface. <EOS>