Thermal Mass in Log Walls

Thermal Mass is a term used by many people to explain the way a heavy log wall provides insulation vs traditional insulation and R-Value scales.  Dense, thick wood in a large log holds it's temperature longer than a regular stick-frame wall. Think of a stone placed next to a fireplace. The stone warms up, and stays warm even after the fire burns down.  That is an example of thermal mass at work.

This effect is most noticeable during times of temperature fluctuation where the days are warm and nights are cold.  The log wall will stay virtually the same temperature.  This can greatly reduce your energy costs to heat and cool during the spring and fall, and your log walls can effectively cool your home in the summer, and help heat it in the winter.  Log homes differ from some other construction materials because solid wood has both moderate R-value (insulation) and also significant thermal mass. In contrast, water, earth, rocks, and concrete all have low R-values.  Wikipedia has a great article on Thermal Mass here