A board system for decking, cladding, or roofing, comprising a first board and a second board; a support element for supporting the first board and the second board; and a connecting device configured to releasably fasten the the first board and the second board to the support element, wherein the support element comprises at least one lateral surface, and at least one locking member arranged on said lateral surface; and the connecting device comprises at least one arm with a locking member configured for engagement with the locking member of the support element, a first holding member for locking the first board transversally relative the connecting device, the first board comprising a first groove extending in the longitudinal direction of the first board, having an opening that faces towards a top side of the first board, and being configured to at least partially receive the first holding member, and at least one of the locking member of the support element and the locking member of the connecting device comprises a plurality of protrusions (9, 10) forming a plurality of locking positions of the connecting device relative the support element, characterised in that the connecting device further comprises a second holding member for locking the second board vertically relative the connecting device, the second holding member comprising a protrusion with a release surface that extends in the transversal direction of the connecting device and faces towards the locking member of the connecting device, wherein the protrusion is configured to extend into a third groove of the second board that extends in the longitudinal direction of the second board and that has an opening facing in the transversal direction of the second board. a support element for supporting the first board and the second board; and a connecting device configured to releasably fasten the the first board and the second board to the support element, wherein the support element comprises at least one lateral surface, and at least one locking member arranged on said lateral surface; and the connecting device comprises at least one arm with a locking member configured for engagement with the locking member of the support element, a first holding member for locking the first board transversally relative the connecting device, the first board comprising a first groove extending in the longitudinal direction of the first board, having an opening that faces towards a top side of the first board, and being configured to at least partially receive the first holding member, and at least one of the locking member of the support element and the locking member of the connecting device comprises a plurality of protrusions (9, 10) forming a plurality of locking positions of the connecting device relative the support element, characterised in that the connecting device further comprises a second holding member for locking the second board vertically relative the connecting device, the second holding member comprising a protrusion with a release surface that extends in the transversal direction of the connecting device and faces towards the locking member of the connecting device, wherein the protrusion is configured to extend into a third groove of the second board that extends in the longitudinal direction of the second board and that has an opening facing in the transversal direction of the second board. at least one arm with a locking member configured for engagement with the locking member of the support element, a first holding member for locking the first board transversally relative the connecting device, the first board comprising a first groove extending in the longitudinal direction of the first board, having an opening that faces towards a top side of the first board, and being configured to at least partially receive the first holding member, and at least one of the locking member of the support element and the locking member of the connecting device comprises a plurality of protrusions (9, 10) forming a plurality of locking positions of the connecting device relative the support element, characterised in that the connecting device further comprises a second holding member for locking the second board vertically relative the connecting device, the second holding member comprising a protrusion with a release surface that extends in the transversal direction of the connecting device and faces towards the locking member of the connecting device, wherein the protrusion is configured to extend into a third groove of the second board that extends in the longitudinal direction of the second board and that has an opening facing in the transversal direction of the second board.