Recently, I read a sobering report about energy use by homes in the US on a website called buildinggreen.com:

 "There are 124 million housing units in the U.S., according to the U.S. Census Bureau. Of these, about 85 million are site-built single-family homes, 8.6 million are manufactured or mobile homes, and the rest are units in buildings that house multiple families. If we include single-family, multifamily up to four units (which are similar to single-family in design and performance), and manufactured and mobile homes, there are about 103 million existing houses in the country, and it’s these that we focus on in this article.

"The median age of all housing units in the U.S. (including multifamily) is 34 years (built in 1973), meaning that 50% are older and 50% are newer; 77% were built in 1950 or later.

"In 2004, residential buildings in the U.S. used 21.1 quads (22 million terajoules) of energy, or 21% of the nation’s total primary energy consumption and 36% of total electricity consumption. (Primary energy is that energy contained in, or used to produce, the fuels and electricity we consume; it includes the fuel that utility companies use to generate electricity rather than the electricity itself.) On a per-household basis in the U.S., total primary energy consumption in 2004 was 185 million Btus (195 gigajoules), and total delivered energy consumption was 101 million Btus (107 gigajoules). Within the residential sector, the largest users of primary energy are shown in the table below. In different regions of the country, this split among energy end-uses is quite different; the share for space cooling, for example, is significantly higher in the South than it is in the rest of the country.

"As for impact on global warming, the greenhouse gas emissions associated with residential energy use in the U.S. in 2005 totaled 330 million metric tons carbon equivalent. This represents 20.5% of total carbon emissions for the U.S. and nearly equals the total carbon emissions of Japan, whose economy ranks second to the U.S. but whose carbon emissions rank fourth—well behind China (now number one), the U.S., and Russia. Interestingly, of the carbon dioxide production attributed to our residential buildings, 70% is from electricity use and only 30% is from direct combustion of fossil fuels."

So, electricity use in US homes is responsible for nearly 15% of carbon emissions in the US. Total carbon output from US homes is equal to the total carbon output from the nation of Japan (and Japan ranks fourth in the world for carbon emissions). Yikes. That's a lot of carbon.

There are standards for new construction that will make those structures much more energy efficient, but when it comes to our homes, remember, over half of the existing homes are more than 30 years old, and thus are less likely to have been built with energy conservation as a priority.

These facts highlight the importance of retrofitting existing structures - like we are doing with our 99 year old home.

The Intergovernmental Panel on Climate Change recommends that a 2/3 reduction in energy use by existing homes will be necessary as part of the overall effort to move the planet towards a "carbon neutral" state.

 The same report quoted above includes an example of a retrofit project for a 90 year old home near Boston. The owner was renovating the house, and decided to improve the energy efficiency in the process by tightening the house with more insulation, choosing energy efficient windows, etc. She cautioned that it might not be cost effective to do such energy fixes if they were not incorporated into a larger renovation project.

The article concludes with an interesting idea:

"Significantly reducing the energy consumption of existing homes is a critical priority if we are to stem greenhouse gas emissions and global warming. It is also very challenging. Achieving 50% energy savings in an existing home is not as easy as it might seem—but it can be done.  

"The biggest challenges are cost and skilled labor. To address these, EBN’s editorial this month presents the concept of an Environmental Service Corps to focus on home energy retrofits along with such other activities as ecological restoration and invasive species control. A program like this—as bold and unlikely as it seems—would provide only part of the answer to bring about widespread energy retrofitting. We will also need to encourage the use of energy-efficient mortgages and home loans, subsidized low-interest loans, outright grants, and performance-based tax incentives.

"The costs of committing our nation to a cutting-edge program to retrofit a significant percent of our nation’s housing stock would be huge—hundreds of billions of dollars, if not trillions of dollars, over the coming decades. The cost would be on the scale of what we are spending on the Iraq War but arguably with more return on investment for the people footing the bill. The hope is that our political leaders would see the benefits that this investment would provide in the way of energy security, protection against rising energy costs, and environmental stewardship. "