A sealed and thermally insulating tank wherein the distance between two adjacent corrugations of the corrugated metal sheets of the sealing membrane is equal to a predetermined corrugation interval io, the sealing membrane comprising, around a through-element: two notched rectangular metal plates 3io wide in the first direction and 7io long in the second direction, which are symmetrical to one another, each notched rectangular metal plate having three outer edges disposed in line with a plurality of anchor plates and welded onto the first plurality of anchor plates and an inner edge having a notch formed to avoid cutting a square window through which the through-element passes, and two metal retrofit plates disposed between the non-notched portions of the inner edges of the two notched rectangular metal plates.