By Carl Seville
The increased cost of heating and cooling America's homes has gotten a lot of press lately, and consumer publications have had plenty of articles about DIY projects to help reduce those costs in individual houses. After all, homes in most climates require space heating, air conditioning or both, and the majority of the fuels we use to heat and cool our homes come from limited resources. The concept of green building is top of mind for many new-home builders, but green remodeling seems to be less common.
That's too bad. Energy savings are important to homeowners and to society as a whole. When renovated as a high-performance building, a house requires less energy to keep its interior comfortable. Energy-efficient improvements today will save money for the lifetime of the house. And in the big picture, such improvements in 100,000 or more homes will significantly reduce the impact on energy resources throughout our lifetimes.
There are three key components to a high-performance house:
- Energy conservation results from effective design and usage of a house; a small house will conserve more energy than a large one. Other ways to conserve energy include setting the thermostat higher in summer and lower in winter, and keeping doors and windows closed when heating and cooling.
- Energy efficiency is defined as using technology — insulation, air sealing, insulated windows, high-efficiency furnaces, water heaters, lighting, and appliances — to decrease energy demand.
- Renewable energy includes solar hot-water heaters, photovoltaic cells to generate electricity, passive solar heating and passive ventilation.
Remodeling options and building science
In residential remodeling, it is difficult to control the size of a house or how the homeowners will use it. Furthermore, the costs and complexity of renewable energy methods can limit their use. That leaves energy efficiency — decreasing demand through technology — as the low-hanging fruit for remodelers.
This is where the knowledge of building science comes in handy. With little or no increase in cost, homes can be made significantly more efficient, benefiting the owners for years to come. Energy efficiency means dealing with heat and air. Unfortunately, neither is usually a major consideration for remodelers.
The physics of heat
Heat naturally seeks a balance with cold, so given the opportunity, it tends to migrate outdoors in the winter and indoors in the summer. Air movement is its partner in this energy-efficiency crime; uncontrolled air movement in a house causes significant energy loss. A remodeler's goal should be to control the gain and loss of heat, as well as the movement of air.
Heat loss occurs one of three ways:
- Conduction, defined as the transfer of heat through a solid. An example is the wintertime loss of heat through poorly insulated exterior walls of a house.
- Convection, or the transfer of heat through air currents. Think about the movement of air from the soffits to the ridge vents in an attic. Heat rises — especially if it's heated air.
- Radiation, the transfer of heat from surface to surface. An example is the difference between sitting in the sun and the shade on a hot day. The shade is actually blockage of radiated heat from the sun's surface, as well as some of the light.
Consider how each of these forms of heat loss occurs in a house and how you can eliminate them in your projects. In upcoming articles, we will discuss specific ways to use these concepts to make homes more efficient.
Carl Seville, a green builder with more than 25 years of experience in remodeling, is the winner of the NAHB's 2006 National Green Building Award for Remodeled Home of the Year.
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