Structural flooring system, comprising: - at least one primary joist, - at least one secondary joist, - at least one splice plate (6.2) and at least one shear connector (6.1), - at least one slab, the slab comprising a first face (4.1) and a second face (4.2), being the first face (4.1) located in an upper position than the second face (4.2) according to the gravity direction, and - at least one slab reinforcement, wherein - the primary joists are oriented according to a first mounting direction perpendicular to the gravity direction, - the secondary joists are oriented according to a second mounting direction perpendicular to the gravity direction, - the section (2.1) of the primary joists is a built-up section, said section (2.1) is made from at least two individual plates fastened together, such as welded or bolted, thus achieving a structural member, said section (2.1) comprising a first section end (2.2) and a second section end (2.3), being the first section end (2.2) located in an upper position than the second section end (2.3) according to the gravity direction, - the section (3.1) of the secondary joists is a C section, said section (3.1) comprising a first section end (3.2) and a second section end (3.3), being the first section end (3.2) located in an upper position than the second section end (3.3) according to the gravity direction, - each secondary joist comprises an upper flange (3.4) located at the first section end (3.1) and a lower flange (3.5) located at the second section end (3.2), and at least a cantilever portion (3.6) located on one or both ends of the upper flange (3.4), - each primary joist comprises a lower flange (2.5) at the second section end (2.3) and an upper flange (2.4) at the first section end (2.2), wherein the upper flange (2.5) supports a cantilever portion (3.6) of at least one secondary joist, - the lower flange (2.5) of the primary joist and the lower flange (3.5) of the secondary joist (3.5) are pressed together by means of the splice plate (6.2) and the at least one shear connector (6.1), - the slab is located adjacent to the primary joists and to the secondary joists, covering the first section end (2.2) of the primary joist and the first section end (3.2) of the secondary joist, and - the slab reinforcement is located on the first face (4.1) of the slab. - at least one primary joist, - at least one secondary joist, - at least one splice plate (6.2) and at least one shear connector (6.1), - at least one slab, the slab comprising a first face (4.1) and a second face (4.2), being the first face (4.1) located in an upper position than the second face (4.2) according to the gravity direction, and - at least one slab reinforcement, - the primary joists are oriented according to a first mounting direction perpendicular to the gravity direction, - the secondary joists are oriented according to a second mounting direction perpendicular to the gravity direction, - the section (2.1) of the primary joists is a built-up section, said section (2.1) is made from at least two individual plates fastened together, such as welded or bolted, thus achieving a structural member, said section (2.1) comprising a first section end (2.2) and a second section end (2.3), being the first section end (2.2) located in an upper position than the second section end (2.3) according to the gravity direction, - the section (3.1) of the secondary joists is a C section, said section (3.1) comprising a first section end (3.2) and a second section end (3.3), being the first section end (3.2) located in an upper position than the second section end (3.3) according to the gravity direction, - each secondary joist comprises an upper flange (3.4) located at the first section end (3.1) and a lower flange (3.5) located at the second section end (3.2), and at least a cantilever portion (3.6) located on one or both ends of the upper flange (3.4), - each primary joist comprises a lower flange (2.5) at the second section end (2.3) and an upper flange (2.4) at the first section end (2.2), wherein the upper flange (2.5) supports a cantilever portion (3.6) of at least one secondary joist, - the lower flange (2.5) of the primary joist and the lower flange (3.5) of the secondary joist (3.5) are pressed together by means of the splice plate (6.2) and the at least one shear connector (6.1), - the slab is located adjacent to the primary joists and to the secondary joists, covering the first section end (2.2) of the primary joist and the first section end (3.2) of the secondary joist, and - the slab reinforcement is located on the first face (4.1) of the slab.