California residential CO2 emissions

Here is a chart that breaks down California residential CO2 emissions into end-uses.  The data comes from the 2009 CALIFORNIA RESIDENTIAL APPLIANCE SATURATION STUDY Executive Summary.

Space heating and water heating account for nearly 50% of all CO2 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. 

Designing to Passive House standards can cut out most of the active heating and cooling energy.  Solar water heating can cut out most of the Water Heating category.  Daylighting can halve the Lighting category, with low-power electric lights knocking out much of the remainder.  The fun challenge is to implement these concepts cost-effectively, especially for existing buildings, in today's contracting economy.