This article gives an overview of how to model curtain walls for PartL SBEM calculations.
As the modelling of internal glazing, along with with the related heat gain and airflow in between, would be outside the scope of the SBEM calculation engine, a workaround is required to approximate curtain wall constructions.
To do so, the NCM modelling guide instructs that allowances should be made in the frame factor:
Should you need to define this for a particular façade only, then you can do so in Part L under the Misc tab as shown below.
Note that the Frame factor will be the inverse of the Window area - eg if you have 85% glazing you should enter 0.15 for the Frame factor.