2 emissions from residential building stock. The energy source for these is mostly natural gas. Compared to electricity, this fuel is cheap per pound of CO2 generated. This makes it hard to argue for CO2 reductions on the basis of energy cost savings.
Here is the same chart, re-colored to highlight the end-uses that building designers can affect. These end-uses may persist for the life-of-structure: for example, it's costly to change a building's orientation or significantly increase its insulation levels.
This second chart shows that resident choices and behavior (shown in gray) may account for 40% of a building's metered energy consumption. The other 60% (shown in color) may be due to choices made by the designer and equipment specifier.