Energy efficient form finding

Hi everyone,

I’m trying to find a form for a standalone house that is optimized to be energy efficient. I have tried to find an energy efficient form by finding an optimal volume ratio. But that leads to problem with the sizes of the form. I want the house to be around 150 m2. But when I run the simulation, it finds proportions that translates to larger area than 150m2.

Can anyone tell me how I can fix this? Or is my approach wrong?

Thank you

(This is my attempt to learn grasshopper in a practical way.)