A stiffening element comprising at least a first stiffening profile and at least a second stiffening profile, said at least one first stiffening profile and said at least one second stiffening profile together forming a structural surface of said stiffening element, that the at least one first stiffening profile comprises: - a profile member having a first surface and a second surface opposite to said first surface, a length extending in a first direction, a height extending in a second direction, and a width extending in a third direction, said length and said height defining a first plane, - at least one structural flange, wherein at least one edge and/or part of said first surface of said profile member and said at least one structural flange are connected, and said at least one structural flange is extending in a second plane arranged in an angle α to said first plane, and wherein the at least one structural flange is a part of the structural surface, - a through-passage extending through the profile member, along the third direction of said profile member, wherein the through-passage provides an opening in said profile member, and - at least one support flange having a first support surface and a second support surface, wherein at least one edge and/or surface of said support flange is connected to said profile member and/or said structural flange and wherein the support flange is extending in a third plane arranged in an angle β to said first plane and/or arranged in an angle γ to said second plane, the at least one second stiffening profile comprises: - a bottom portion and at least one support side portion, wherein at least one edge and/or surface of said bottom portion and said at least one support side portion are connected and wherein said bottom portion is extending in a forth plane and said at least one support side portion is extending in a fifth plane arranged in an angle δ to said forth plane, wherein the first support surface of the at least one support flange of the first stiffening profile is at least partly arranged adjacently and facing the at least one support side portion of the at least one second stiffening profile; and wherein the at least one support flange is directly or indirectly attached at least partially to the at least one support side portion of the second stiffening profile; wherein said bottom portion is a part of the structural surface; the structural surface of the stiffening element being configured to be assembled to an element surface of at least one structural element; and a surface of the bottom portion is configured to constitute a part of the structural surface of the stiffening element; and characterized in that the second stiffening profile has an essentially U-shaped cross-section when seen in the third direction. - a profile member having a first surface and a second surface opposite to said first surface, a length extending in a first direction, a height extending in a second direction, and a width extending in a third direction, said length and said height defining a first plane, - at least one structural flange, wherein at least one edge and/or part of said first surface of said profile member and said at least one structural flange are connected, and said at least one structural flange is extending in a second plane arranged in an angle α to said first plane, and wherein the at least one structural flange is a part of the structural surface, - a through-passage extending through the profile member, along the third direction of said profile member, wherein the through-passage provides an opening in said profile member, and - at least one support flange having a first support surface and a second support surface, wherein at least one edge and/or surface of said support flange is connected to said profile member and/or said structural flange and wherein the support flange is extending in a third plane arranged in an angle β to said first plane and/or arranged in an angle γ to said second plane, - a bottom portion and at least one support side portion, wherein at least one edge and/or surface of said bottom portion and said at least one support side portion are connected and wherein said bottom portion is extending in a forth plane and said at least one support side portion is extending in a fifth plane arranged in an angle δ to said forth plane,