A mounting system for positioning at least one photovoltaic module of a PV-module unit on a planar flat roof in an inclined position having an angle (alpha) relative to the flat roof, comprising: a frame, wherein the frame defines a PV-module unit mounting side, a back side, two lateral sides, and a bottom side, which commonly define a prism, the base area of which corresponds to one of the lateral sides, the cover area of which corresponds to the other one of the lateral sides, and a jacket area of which corresponds to the mounting side, the back side and the bottom side, wherein the mounting side and the back side enclose a, preferably obtuse, angle (Beta), wherein the mounting side and the back side intersect along an imaginary line of intersection, which defines a ridge being arranged oppositely to the bottom side, and wherein the bottom side is arranged, in an installed state of the mounting system, oppositely to the flat roof; a side-covering for each of the lateral sides, wherein each of the side-coverings covers the associated lateral side; a wind deflector attached to the back side and covering the back side; characterized in that in a region of the ridge between the wind deflector and the PV-module unit, if the PV-module unit is attached to the mounting side, an open ridge gap is formed connecting an interior of the prism to an outer environment of the prism, wherein a perpendicular projection of the ridge gap onto the flat roof defines a first area; wherein in a lower region of the mounting side between the flat roof and the attached PV-module unit a first open foot gap is formed and/or in a lower region of the back side between the flat roof and the wind deflector a second open foot gap is formed, wherein a perpendicular projection (A21, A22) of each of the foot gaps (50, 52) onto a first imaginary plane, which is oriented perpendicular to the flat roof, respectively defines a second area; wherein the first area is at least as great as a sum of all of the second areas; and wherein an upper edge of the wind deflector and an upper edge (98; 102) of the PV-module unit are arranged in a second imaginary plane, which is oriented parallel to the flat roof. a frame, wherein the frame defines a PV-module unit mounting side, a back side, two lateral sides, and a bottom side, which commonly define a prism, the base area of which corresponds to one of the lateral sides, the cover area of which corresponds to the other one of the lateral sides, and a jacket area of which corresponds to the mounting side, the back side and the bottom side, wherein the mounting side and the back side enclose a, preferably obtuse, angle (Beta), wherein the mounting side and the back side intersect along an imaginary line of intersection, which defines a ridge being arranged oppositely to the bottom side, and wherein the bottom side is arranged, in an installed state of the mounting system, oppositely to the flat roof; a side-covering for each of the lateral sides, wherein each of the side-coverings covers the associated lateral side; a wind deflector attached to the back side and covering the back side; characterized in that in a region of the ridge between the wind deflector and the PV-module unit, if the PV-module unit is attached to the mounting side, an open ridge gap is formed connecting an interior of the prism to an outer environment of the prism, wherein a perpendicular projection of the ridge gap onto the flat roof defines a first area; wherein in a lower region of the mounting side between the flat roof and the attached PV-module unit a first open foot gap is formed and/or in a lower region of the back side between the flat roof and the wind deflector a second open foot gap is formed, wherein a perpendicular projection (A21, A22) of each of the foot gaps (50, 52) onto a first imaginary plane, which is oriented perpendicular to the flat roof, respectively defines a second area; wherein the first area is at least as great as a sum of all of the second areas; and wherein an upper edge of the wind deflector and an upper edge (98; 102) of the PV-module unit are arranged in a second imaginary plane, which is oriented parallel to the flat roof.