The following picture shows two different situations with solar radiation to a plate. Heat leaving the plate through radiation, convection and conduction in plate. Under the plate there is a boundary layer. In both cases gravity acts downward and there is no forced wind blowing.

NO SPACE:

In first situation the plate is located on the boundary layer, which means that the plate is isolated from the buttom.

WITH SPACE:

In the other case the plate is liftet.

I want to find the temperatures in those two cases. But it seems that i cannot isolate the plate completely, In the situation with no space heat is being transfered through the boundary layer, see figure below. I have tried the following; real wall with 0 heat transfer coefficient. Ideal wall. Choosing rockwool with a thickness, nothing works. Heat is being transfered through the wall as you see.

So my question is; how can i isolate heat transfer completely from a boundary??

the top layer is supposed to be ordinary material, and the buttom layer is suppose to represent a bounday layer