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Our Spring, 2017 Newsletter is Here!


Test proves that Log Homes are more Energy-Efficient than Conventional Homes
by Steve Lykins

It is a common misconception among the public as well as many Architects, Engineers and Builders, that solid log homes use an antiquated building technique. Some might even say that solid log homes are not relevant in today’s energy-conscious building atmosphere. However, when we apply current log construction techniques and we use current technology to test solid log homes against conventional stick framed homes, the results are often surprising to skeptics as well as proponents of log construction. Indeed log homes are relevant in today’s ‘green’ building environment. In fact, those who understand the building science through testing might consider log homes to be high performance homes.

Probably one of the most credible and therefore popular tests in recent history was performed by the National Bureau of Standards during a 28 week period from 1981-1982 near Washington, D.C. This test was named “Mass Wall Field Study.” The purpose of the experiment was to study the thermal mass effect of a solid log home and how it impacts energy usage of a solid log home versus a conventional stick framed home. The test period included a winter heating season (January - April), an intermediate heating season (April - May) and a summer cooling season (July – September). The buildings and their solar orientation were identical besides the exterior wall construction. One of the test buildings had exterior walls consisting of solid, 7-inch square lodge pole pine log construction with a tongue & groove locking system, which had a tested R-Value of 9.25. Another building had exterior wall construction consisting of painted 0.625-inch exterior plywood sheathing, 2x4 studs at 16-inches on center, R-11 batt insulation between studs, a 0.002-in. polyethylene vapor barrier and 0.5-in. gypsum board on the interior. This wall construction had a tested R-value of 11.14.

Here are some basic observations about the energy consumption of the buildings based on the results of the testing. The solid log walls contained approximately four times as much mass as the stick framed walls. The solid log walls absorbed more than two times as much heat from the sun in the winter (when the sun is low in the sky) than in the summer (when the sun is high in the sky). The stick framed building used approximately the same amount of energy as did the solid log building during the winter heating season, so a significant thermal mass effect was not observed during the winter heating season. The stick framed building used approximately 32% more energy than the solid log building during the summer cooling season and approximately 82% more energy than the solid log building during the intermediate heating season, so during the intermediate heating season (spring/autumn) as well as the summer cooling season, a significant thermal mass effect was observed. Across all seasons, the solid log building performed about 38% better than the stick framed building, even though the tested R-value of the solid log wall was about 20% less than the tested R-value of the stick framed wall.

The following conclusions can be made from the results of the experiment. The exterior walls of a solid log home have the ability to absorb and store thermal energy and then release it at a later time, much like a battery stores electrical energy. Further, the amount of solar energy absorbed by the logs is determined by the angle of the sun. A log wall will naturally absorb about twice as much solar energy in the winter (when it is needed) than in the summer (when it is not needed). One might think of logs as a “smart” building material. The thermal mass effect of a solid log home is most beneficial when heating/cooling is not constantly supplied by the heating/cooling equipment (during spring, summer and fall). Even in the winter heating season, when the thermal mass effect of a solid log home is not as great, a solid log home still insulates about the same as a conventional stick framed home.

For years, owners of solid log homes have told me that their homes are more energy efficient than any conventional stick framed home they have ever owned. As a skeptic, I had to see some scientific test data to support this claim. This testing proves that it costs less money annually to heat and cool a solid log home than a conventional stick framed home in all but the coldest climates (like northern Alaska, climate zone 8). Even in the coldest of climates a solid log home will likely cost about the same amount of money annually to heat as would a conventional stick framed home.

Although this test was performed more than 30 years ago, solid log home construction techniques and materials have improved significantly during that time, specifically through the use of dimensionally stable kiln dried, precision milled logs and a gasketed tongue & groove air sealing system. During the same 30 year period conventional stick framed home construction techniques have remained nearly unchanged besides a greater emphasis on air sealing and insulation R-value. As the results of this experiment show, R-value alone does not describe the overall thermal performance of a home. When we do consider all factors that affect energy usage in a home, it is clear that solid log homes are, in fact, high performance, low energy usage homes built from a highly sustainable material. This is exactly what educated homeowners demand in today’s energy-conscious building atmosphere.

All observations and conclusions are based on the data presented in the technical paper “A Field Study of the Effect of Wall Mass on Heating and Cooling Loads of Residential Building”. The paper was authored by D.M. Burch, W.E. Remmert, D.F. Krintz and C.S. Barnes and was originally presented at the Building Thermal Mass Seminar at Oak Ridge National Laboratory in Oak Ridge, TN on June 2nd, 1982.