To follow up on this matter; guidance on how to set up custom layers can be found here .

Hi Kostas, You can enter the thermal properties of the material by selecting Special Solid Layer, at the bottom of the Layer Type list:

Hi Roy, it may depend on the type of calculation you are doing as to the best solution. The simplest option is to create an Exposed Wall in Fabric Data using the layer data for the above ground wall. Once created you can adjust the calculated U-Value…

Chris You should set up a 'Ground floor' in Fabric to represent your construction, and use this in your model. Note, however, that the Ground Floor part of the Fabric program doesn't calculate the U value for the surface, so you should use the Mat program…