Benefits of Thermal Mass in Log and Timber Homes

One difference between log homes and traditional construction is the concept of thermal mass.

One of the first questions we are asked when customers visit a model home or our booth ant a Log Home Show is “What is the ‘R’ value of your logs?”! We then spend many minutes explaining that the method by which the energy of logs are measured is ‘Thermal Mass’ and not ‘R’ Value.

In this months newsletter we would like to share some of that and give you references so that you can delve deeper in to the subject.

R Value vs. Thermal Mass

  • ‘R’ – value measures a material’s resistance to the transfer of heat from one side to another. Logs have a relatively low resistance to heat transfer as they actually absorb and store heat in their cellular structure. Thus taking a longer period of time to transfer through the material.
  • Thermal Mass is a material’s capacity to absorb, store and slowly release heat over time.

Back in the early 90’s the Log Home Council (LHC) set out to prove two things.

  1. First, logs have a thermal mass because of their cellular structure , bulk and thickness.
  2. Second, this thermal mass provides significant energy saving benefits because it releases heat back into the house when temperatures drop.

The first study focused on heat loss through the log wall compacted to a conventional framed wall. The finding was that leakage occurred in the same places as a framed house, at the peak of cathedral ceilings, around window and door frames and at tops of walls. It concluded that the leakage was not due to the log walls.

The second study concluded that the thermal mass of log walls does significantly reduce energy use for heating in cold climates.

Therefore, after 13 years the Nations Model Energy Code finally recognized the energy conservation benefits of ‘Thermal Mass’. This recognition was the goal of the LHC a part of the Building Systems Council of the National Association of Home Builders (NAHB).