All but the most ardent skeptics agree that climate change is occurring. Although the ramifications and causes are debatable, nearly everyone agrees that man-produced CO2 is a major contributor to climate change and global warming. It is a fact that the operation of residential buildings in the U.S. comprises 21% of our energy consumption. Other statistics are even more convincing. We must do more to reduce energy consumption, and thereby CO2 contributions, in our homes and buildings.
Small strides are made
With everyone trying to green their lifestyles, small changes have made an impact. Compact fluorescent bulbs (or CFLs) save energy, and energy-efficient appliances are now the norm. Low-emittance and multiple-paned glazing systems have been around for decades. But the biggest change—the one that can have the greatest impact—is a change in the basic methods and materials to construct America's buildings. The technology to build the most energy-efficient, durable, and comfortable homes is available in concrete housing systems. Yes, cement production is a large contributor to CO2 emissions. But significant progress has been made in the efficiency of cement manufacturing. Cement comprises only about 10% of the concrete mix, and concrete homes have the ability to last for centuries.
How do concrete homes save energy? Concrete's thermal mass has tremendous heat storage capacity, which means that maintaining a desired temperature is easier and uses minimal energy input. Lower, slower temperature swings also make a house more comfortable. A 4- to 6-inch thermal mass located on the warm side or interior of an insulation system contributes significantly to the energy efficiency of a home, and the amount of insulation significantly reduces when thermal mass is factored into energy use needs. In some parts of the country, especially those where the temperature gets too hot during the day and too cold during the night, insulation may be eliminated.
However, most parts of the U.S. need an insulation system to attain optimum energy performance. Location of the insulation system is important. The contribution of mass isolated from the interior space, or positioned on the exterior of a structure, significantly reduces the performance of a structure with thermal mass, so a system that puts the mass on the interior is most efficient. There are several systems on the market that use sandwich walls or walls with exterior insulation. To finish this type of wall, a modern design might use exposed or sandblasted concrete.
Fresh air, moisture control
Another aspect of energy conservation in concrete homes is controlling infiltration or air leakage from the outside. Outside air brings in cold, humidity, and pollutants. Although a certain amount of outside air is desirable, controlling air infiltration is preferable. Older uninsulated homes with loose double-hung windows have uncontrolled air infiltration rates (air changes per hour) as high as 3 or 4. Homes with exterior concrete walls and high-quality windows and doors produce infiltration rates as low as 0.1. An air exchange that low can be unhealthy, so there must be a way of introducing a controlled flow of fresh air when needed.
Another concrete home energy saver is a reduction in the size and cost of the heating and cooling system. Mechanical systems typically are sized to handle the most extreme external design conditions. The thermal efficiency and airtightness of a concrete home allow a significant reduction in heating and cooling loads. A supplier or engineer experienced in sizing systems for energy-efficient structures should be consulted. An oversized system will cycle on and off more frequently and will not provide the necessary humidity control.
Double-walled, enveloped, and super-insulated wood-frame construction, earth-sheltering, and other concepts that were popular in the 1970s again are being promoted and built. The concrete home, however, will use fewer resources, last longer, be easier to maintain, provide greater durability and comfort, and contribute to reducing global warming.