We’ve already proven we can do it (see "The proof is in the numbers")—so now we are formalizing the process and guaranteeing—that with careful design, we can construct an addition without adding to the fossil fuel energy use of the existing house.

In fact—we’ve given this a name (and applied for registration of our service mark)—we call it “the zero-net” addition.

In this example, the back wall of the existing house had leaky windows and no insulation—by building beyond it, with carefully detailed floors, walls, and roof—which lose very little heat in winter, and gain very little in summer—fuel use for air conditioning and heating did not increase, even though the floor area of the house was increased by nearly 15%.

In the case of a newer home—where the building envelope is more efficient to begin with, we will add solar collectors, and employ other active and passive strategies to “zero-out” the energy consumption of the new, added space.

Or, we may combine strategies—and actually reduce net energy consumption.