A building system for constructing a building, the system comprising: - plurality of prefabricated elements, the element comprising: -- a self-supporting insulation panel comprising a rigid insulation material and having two straight and parallel edge surfaces (6a, 6b), and an outer and inner surfaces (8, 9), -- a metal frame, comprising a pair of sub-frames, a first sub-frame attached to a first edge surface and a second sub-frame attached to a second edge surface of the insulation panel, -- the sub-frame (7a, 7b) extending along the length of the insulation panel, - the length of the sub-frame (7a, 7b) having a cross-section comprising --- an attaching arm extending along the corresponding edge surface (6a, 6b), and --- an intruding section arranged in the attaching arm and in an angle respect to that, the intruding section intruding into the insulation panel, and --- a box-type structure arranged distally from the intruding section and comprising walls and corners constituting a closed or partly open construction, --- the box-like structure extending from the attaching arm and being arranged on the outer surface or on the inner surface of the insulation panel, the building system further comprising - a connecting element, being at least essentially as long as the sub-frame (7a, 7b) and having a cross-section comprising two arms (15a, 15b) and a connecting section connecting said two arms, the cross-section having basically a shape of an U-profile, the connecting element, in use, being arranged on said sub-frames (7a, 7b) of two adjacent elements, said arms (15a, 15b) being situated on opposite side of the two sub-frames (7a, 7b) and keeping together said sub-frames (7a, 7b) of adjacent elements. - plurality of prefabricated elements, the element comprising: -- a self-supporting insulation panel comprising a rigid insulation material and having two straight and parallel edge surfaces (6a, 6b), and an outer and inner surfaces (8, 9), -- a metal frame, comprising a pair of sub-frames, a first sub-frame attached to a first edge surface and a second sub-frame attached to a second edge surface of the insulation panel, -- the sub-frame (7a, 7b) extending along the length of the insulation panel, -- a self-supporting insulation panel comprising a rigid insulation material and having two straight and parallel edge surfaces (6a, 6b), and an outer and inner surfaces (8, 9), -- a metal frame, comprising a pair of sub-frames, a first sub-frame attached to a first edge surface and a second sub-frame attached to a second edge surface of the insulation panel, -- the sub-frame (7a, 7b) extending along the length of the insulation panel, - the length of the sub-frame (7a, 7b) having a cross-section comprising --- an attaching arm extending along the corresponding edge surface (6a, 6b), and --- an intruding section arranged in the attaching arm and in an angle respect to that, the intruding section intruding into the insulation panel, and --- a box-type structure arranged distally from the intruding section and comprising walls and corners constituting a closed or partly open construction, --- the box-like structure extending from the attaching arm and being arranged on the outer surface or on the inner surface of the insulation panel, --- an attaching arm extending along the corresponding edge surface (6a, 6b), and --- an intruding section arranged in the attaching arm and in an angle respect to that, the intruding section intruding into the insulation panel, and --- a box-type structure arranged distally from the intruding section and comprising walls and corners constituting a closed or partly open construction, --- the box-like structure extending from the attaching arm and being arranged on the outer surface or on the inner surface of the insulation panel, - a connecting element, being at least essentially as long as the sub-frame (7a, 7b) and having a cross-section comprising two arms (15a, 15b) and a connecting section connecting said two arms, the cross-section having basically a shape of an U-profile, the connecting element, in use, being arranged on said sub-frames (7a, 7b) of two adjacent elements, said arms (15a, 15b) being situated on opposite side of the two sub-frames (7a, 7b) and keeping together said sub-frames (7a, 7b) of adjacent elements.