The rules regarding energy efficiency and thermal insulation may seem complicated for an architect, involving numerous calculations and engineering knowledge. At the end of studying them, we often find ourselves asking: "So, what exactly should I know!?". This workshop aims to simplify and logically explain these calculations and aspects, facilitating the understanding of how the rules apply to design in general, and to technical drawings in particular. The importance of this fundamental requirement is amplified by current challenges related to energy efficiency, as well as by the comfort and health standards that these challenges are linked to. The G calculation is one of the applied tools to ensure compliance with this fundamental requirement, and understanding it can facilitate making important design decisions in the search for the best result.