There is sometimes confusion about the energy efficiency of log homes as compared to traditional stick-built homes. Let us explain how log homes, because of thermal mass benefits, are considered by the National Association of Home Builders, Log Homes Council, to be 2.5% - 15% more energy efficient that comparable stick-built homes.

There are two primary factors that determine the ability of a wall to be an effective barrier to temperature differences. One is "R-Value" (Btu/ft2/hour/oF), which is a numerical measure of a material's resistance to heat flow over a defined thickness of that material. Second is "thermal mass," which is a measure of a material's ability to store heat and thereby delay heat flow.

Heat flows by three mechanisms: conduction, convection, and radiation.

• Conduction is the molecule-to-molecule transfer of kinetic energy. For example, a cast iron skillet handle heats up because of conduction through the metal.
• Convection is the transfer of heat by physically moving the molecules from one place to another. For example, forced air heating systems work by moving the heat from one place to another.
• Radiation is the transfer of heat through space via electromagnetic waves (radiant energy). For example, a campfire can warm you even if there is wind between you and the fire, because the radiated heat is not affected by air.

Mass enhanced R-Value: when people refer to the “mass effect” or “effective R-Value,” they are generally referring to the ability of high mass materials to achieve better energy efficiency performance.

Conventional framed walls typically use fiberglass insulation and have an R-Value of about R-13 to R-19. Fiberglass is a good, lightweight insulating material that traps air within its fibers and is therefore a poor conductor of heat. It, however, has very low mass and does not store heat well either.

Log walls are dense and heavyweight, making them poorer insulators of heat than air-filled fiberglass walls. In fact, a log wall the same thickness as an insulated wall (about 6-7 inches) would only have an R-Value of about R-9. However, the high density of solid wood also creates an important "mass effect." Instead of heat being conducted through a log wall, as the lower R-Value might suggest, the heat is actually stored in the logs and significantly delayed in its release. This allows, for example, high outside temperatures to be effectively blocked and stored during the hottest part of the day, and released during the cooler night. This interesting phenomenon is referred to as "thermal capacitance" or time-lag. Solid logs therefore act like “thermal batteries,” storing heat during the day and releasing it at night. Assuming other parts of the log home, such as roof, floors, windows, and doors, are insulated to the same efficient level as the structure, these homes can cost significantly less to heat and cool. Many log homes in cold climates are heated with nothing other than a single fireplace or stove.

For More Information Look for the report, "The Energy Performance of Log Homes" by the Log Home Council at www.loghomes.org