A building construction having a curtain wall construction defined by an interior wall surface including one or more vertical framing members, a spandrel area and at least one floor spatially disposed from the interior wall surface of the curtain wall construction defining a safing slot extending between the interior wall surface of the curtain wall construction and an outer edge of the floor comprising: a thermally insulating and sealing system for effectively thermally insulating and sealing of the safing slot characterized in that said thermally insulating and sealing system comprises Z i) a first element comprising a cavity having an interior wall surface and an opening, positioned substantially in the height of the floor, wherein the cavity is located in the spandrel area of the interior wall surface of the curtain wall construction wherein the cavity of the first element is a compartment having a base and at least two sides, preferably perpendicular or trapezoidal, to the base with an opening parallel to the base, positioned substantially in the height of the floor, within the spandrel area of the interior wall surface of the curtain wall construction so that its opening is parallel and pointing away from the exterior wall surface of the spandrel area, and ii) a second element comprised of a thermally resistant and/or air tight material for insulating, positioned at least partially in the cavity of the first element, wherein the second element includes: a) an inner end surface positioned in abutment with respect to the outer edge of the floor for sealing thereadjacent, b) an outer end surface positioned in abutment with respect the interior wall surface of the cavity, c) a lower facing surface extending between the inner end surface and the outer end surface and facing downwardly therebetween, and d) an upper facing surface extending between the inner end surface and the outer end surface and facing upwardly therebetween, the thermally insulating and sealing system further comprises a connecting third element comprised of a thermally resistant and/or air tight material for insulating, positioned in front of the vertical framing member and in abutment with respect to the second element, the third element being of a T-shaped form, and wherein the second element comprises additional recesses for receiving parts of the third element. i) a first element comprising a cavity having an interior wall surface and an opening, positioned substantially in the height of the floor, wherein the cavity is located in the spandrel area of the interior wall surface of the curtain wall construction wherein the cavity of the first element is a compartment having a base and at least two sides, preferably perpendicular or trapezoidal, to the base with an opening parallel to the base, positioned substantially in the height of the floor, within the spandrel area of the interior wall surface of the curtain wall construction so that its opening is parallel and pointing away from the exterior wall surface of the spandrel area, and ii) a second element comprised of a thermally resistant and/or air tight material for insulating, positioned at least partially in the cavity of the first element, wherein the second element includes: a) an inner end surface positioned in abutment with respect to the outer edge of the floor for sealing thereadjacent, b) an outer end surface positioned in abutment with respect the interior wall surface of the cavity, c) a lower facing surface extending between the inner end surface and the outer end surface and facing downwardly therebetween, and d) an upper facing surface extending between the inner end surface and the outer end surface and facing upwardly therebetween, the thermally insulating and sealing system further comprises a connecting third element comprised of a thermally resistant and/or air tight material for insulating, positioned in front of the vertical framing member and in abutment with respect to the second element, the third element being of a T-shaped form, and wherein the second element comprises additional recesses for receiving parts of the third element. a) an inner end surface positioned in abutment with respect to the outer edge of the floor for sealing thereadjacent, b) an outer end surface positioned in abutment with respect the interior wall surface of the cavity, c) a lower facing surface extending between the inner end surface and the outer end surface and facing downwardly therebetween, and d) an upper facing surface extending between the inner end surface and the outer end surface and facing upwardly therebetween,