PSI date for thermal bridging is decided by the construction type. Selecting metal clad constructions can appear to generate excessive thermal bridging.
Any "Metal Clad" constructions set up and used in your project will be included in a PartL/SBEM calculation. For example, Hevacomp default wall type "Wall Type 2 - Lightweight wall" has a 3mm steel layer defined on the inside and outside of the construction. This type of wall would be classed as "Metal Clad" when passed into the SBEM calculation engine.
Constructions defined as "Metal Clad" consider increased Thermal Bridging in the SBEM calculation engine, resulting in increased heat losses across these constructions.
Thermal properties for a fabric can be fixed within Design Database, including the U-value of a construction to meet Government requirements. However the SBEM calculation engine will still consider these constructions to be "Metal Clad" resulting in higher heating demand results. For example, the "Energy consumption be End Use" may be considered excessive when compared with the notional building.
Care must be taken ensuring that construction components are selected correctly. Modifying Thermal Properties alone will not ensure that a surface is treated correctly, if it is in fact "Metal Clad" when a non-clad surface is required.
The Alpha Value (see this article for more information) reported on the Technical Data Sheet should be checked to ensure the value is not excessive for the Actual Building compared to the Notional Building.