The house is on a slope. The top floor is the living quarters and is 2,300 sq. ft.. The bottom floor is storage and mechanical with no windows and only one exterior door.
The bottom floor is all above ground with the exception of the east end which faces the fill under the garage. The bottom floor is the same size as the top floor, but due to the slope of the ground, the ceiling is only 6' at the east end, so I call it 1,700 sq. ft. So, I have at least 4,000 sq. ft. of conditioned space, all above ground.
All of the duct work is in the bottom floor and feeds wall stacks with vents about a foot below the 10 foot ceilings in the top floor.
The house has 3 foot eves and large porches which shade all of the windows on the north & south. The east is shaded by the garage. The west has 3 small windows tucked up under the eves. They have very low e glass and don't get any sun until after 6. The rest of the windows in the house don't see any sun at all during the summer.
The attic has R49 insulation. The walls have 2" of polyiso foam board between the sheathing and the brick, all sealed with aluminum foil tape. I spent a lot of effort air sealing the house while in construction. I sealed the outlets, sealed the top plates, added gaskets behind the drywall, and spent a few hours in the attic with a foam gun before the insulation was blown in. On the walls, between the polyiso foam and the sheathing is a peel & stick roofing membrane that is completely air & water tight.
I heat & cool at least 4,000 sq. ft. with one 2 ton heat pump in north central Texas.