Modeling a single glazing window with roller shade with distance between shade and glazing

[afshin faramarzi]

Hi,

I am trying to model a single glazing window with an interior roller shade that has a 5 cm gap between the shade and glazing. I have attached the image of my model. I have a question! How I can model the 5 cm gap between shade and glazing? should I put the gap thickness as 5 cm or I should put the Dright distance as 5 cm? I am assuming that the gap is considered as the vacuum space which is something like the gap in double glazing windows! but in my case, the gap is not vacuum. 

Thanks,