How do I model a concrete roof which is planted (i.e. earth & grass) on top?

Work out the R value of the thickness of the soil using the simple R Value calculation tool and add this R value to insulation of the concrete roof.

The attached R Value calculation was based on 350mm soil and grass = R0.3.

The R0.3 was then modelled within the roof zone section to represent represent the concrete planted roof - as per attached.

Ensure the concrete is selected for the ceiling construction.