A joinery element for a building bay, such as a window, a door or a French window, which joinery element comprises a fixed frame on which is added at least one opening frame, which fixed frame is consisted of metal structure profiles, an inner one and an outer one assembled to each other by means of a thermal bridge breaking profile, which fixed frame includes an inner surface forming a L-shaped rebate, in the general shape of a straight dihedron, into which the opening frame is positioned in the closed position, which fixed frame rebate is consisted of: a) a bottom surface (13 b), opposite the peripheral edge of the opening frame in the closed position, formed by - a metal wall of said inner structure profile, - an inner surface of said thermal bridge breaking profile, and - a metal wall (11 b) of said outer structure profile, and b) a lateral surface (13 a), intended to be oriented toward the inside of the building and opposite the outer part of the opening frame in the closed position, formed by a metal lateral wall (11 a) of said outer structure profile, which metal wall (11 a) forming said rebate lateral surface (13 a), et which metal wall (11 b) forming a part of said rebate lateral surface (13 b), extending square relative to each other, and which fixed frame rebate is equipped with at least one added thermal insulation profile that covers at least one part of the bottom (13 b) and lateral (13 a) surfaces of said fixed frame rebate, which thermal insulation profile has a thermal conductivity coefficient lower than that of the metal material constitutive of said structure profiles (10, 11) of the fixed frame, characterized in that said thermal insulation profile added in the rebate has a generally L-shaped section, and includes: (i) a lateral wing (15 a), covering at least one part of said metal lateral wall (10 a) of the fixed frame rebate, and (ii) a return wing (15 b), covering at least one part of said metal square wall (11 b) of said rebate. a) a bottom surface (13 b), opposite the peripheral edge of the opening frame in the closed position, formed by - a metal wall of said inner structure profile, - an inner surface of said thermal bridge breaking profile, and - a metal wall (11 b) of said outer structure profile, and b) a lateral surface (13 a), intended to be oriented toward the inside of the building and opposite the outer part of the opening frame in the closed position, formed by a metal lateral wall (11 a) of said outer structure profile, which metal wall (11 a) forming said rebate lateral surface (13 a), et which metal wall (11 b) forming a part of said rebate lateral surface (13 b), extending square relative to each other, and which fixed frame rebate is equipped with at least one added thermal insulation profile that covers at least one part of the bottom (13 b) and lateral (13 a) surfaces of said fixed frame rebate, which thermal insulation profile has a thermal conductivity coefficient lower than that of the metal material constitutive of said structure profiles (10, 11) of the fixed frame, characterized in that said thermal insulation profile added in the rebate has a generally L-shaped section, and includes: (i) a lateral wing (15 a), covering at least one part of said metal lateral wall (10 a) of the fixed frame rebate, and (ii) a return wing (15 b), covering at least one part of said metal square wall (11 b) of said rebate. (i) a lateral wing (15 a), covering at least one part of said metal lateral wall (10 a) of the fixed frame rebate, and (ii) a return wing (15 b), covering at least one part of said metal square wall (11 b) of said rebate.