A log home’s energy efficiency is based on the wood’s insulation properties and its thermal mass. Insulation refers to the wood’s ability to resist heat transfer. The insulating value of such materials is expressed as its R-value, which signifies the amount of heat loss through the material. Testing has shown that log homes often are more energy efficient than conventional homes boasting higher R-values.
How can this be? It’s because of thermal mass. The sun warms the logs during the day and releases that stored heat at night. During the summer, the logs’ mass slows the transfer of heat into the home, keeping the home cooler. Thicker logs absorb and radiate more heat than their slimmer counterparts, so it makes sense to build with large logs in a location that sees extreme weather.
See also Solar Power: Here Comes the Sun