What is a thermal envelope?
The thermal envelope is the outside shell of a building, whether it’s floors, walls or roofs. The better insulated and less drafty the thermal envelope is, the more effective it is going to work. Energy (heat or cold) tends to act like water in that it will find the area of least resistance to move, so if there is a weak point in the thermal envelope you can loose a lot of energy through this area.
Weak points in buildings may be open downlights, which are not insulated over the top, drafty windows or doors, or a normal “internal” door used between the home and a drafty garage. For high performance homes, the thermal envelope normally ends at the entrance to the garage, and a fully sealed or even a normal exterior door will be used at this point. It is important to try and insulate your floors (or slab), walls and ceiling.