The Stow house and Sudbury house both had semi active solar systems; hot winter air collected in the sun rooms was ducted to the basement where the heat was stored in the mass of the basement walls. In addition, the peak of the sun rooms central air distribution plenum in the Sudbury house had a whole house fan to induce a cool breeze through the house during the summer months.

Since 1989, Carl has developed a standardized set of energy-efficient design build principles and details, which include Air Tight Construction, Fresh Air Ventilation, Sun Tempering (the true benefit of solar heating is the way a house is daylighted), and if the orientation is solar compatible, the use of the Solar Staircase^TMfor sunlight control.