This part 2 of the standard gives the specifications for a two-dimensional geometrical model of a linear thermal bridge for the numerical calculation of: - the linear thermal transmittance of the linear thermal bridge; - the lower limit of the minimum surface temperatures. These specifications include the geometrical boundaries and subdivisions of the model, the thermal boundary conditions and the thermal values and relationships to be used. The standard is based upon the following assumptions: - steady-state conditions apply; - all physical properties are independent of temperature; - there are no heat sources within the building element; - only one internal thermal environment applies; - one or two external thermal environments apply.