Our home loses 25% of heat through the roof, 35% through the walls, 15% through the floor, and rest through windows and gaps around the doors.
To build a better thermal envelope, all you need to do is look at the second law of thermodynamics. According to the second law, “heat flows in one direction, from a warm space to a cold one”.
That means that during the Summer, the warm air from outside will flow to the cooler, interior space. And during the long, Winter months, the warm air inside your home will flow to the cooler air outside. Insulation prevents this.