Thermal performance of logs.

*The 10-years-old-study by the National Bureau of Standards (U.S. government tests) in which the log home out-performed stick-built homes, using less energy for heating and cooling year round.

Because of a property called “thermal inertia (or thermal mass).”

Thermal inertia consist, or mass is the ability of logs to absorb heat from the sun or from man-made heat sources during the day, and radiate that heat back outdoors or into the house at night. That reduces the amount of heat the homeowner must provide with woodstove, solar equipment or conventional heating equipment.

In summer, thermal mass works in reverse. The thermal inertia produces a lag effect, keeping the house cool during the hottest time of the day when air conditioning would be working hardest. The heat stored in the logs dissipates back outside at night, and when the sun rises the cycle begins again.

From NBS, engineering studies have shown that logs have a thermal performance value roughly twice that of their steady-state R-value (real value is 10’’ log = R-22).

Because the R-value of a building material is measured in a laboratory under unchanging conditions, it doesn’t work too well in figuring how insulation will work in the real world, with its ever-changing temprature, sunlight, humidity and building use. To evaluate the quality of ASHRAE’s calculations Dr. Jay McGrew, president of Applied Science and Engineering in Englewood, Colorado, field tested 12 different wall types in five different western coastal and mountain climates. He found that the actual insulation values of log walls were significantly higher than the values set by ASHRAE.

We conclude, then, that the properly designed log house’s true energy economic and thermal performance is as favorable, or more favorable than any of its principal competitors. True energy efficiency not only means that log houses require less energy in their construction and operation, but also log houses are energy efficient in the sense used by N. Georgescu Roegen (Entrophy and the Economic Process), to denote a tendancy to conserve natural ressources (energy, and if managed properly, timber) for the enjoyment of future generations. Log homes last longer, as long as 500 years, if properly maintained.

*Sources: Muir Publishing Co. Inc. (1-2-3) 164, Middle Creek Rd, Cosby, TN 37722, U.S.A.
1- The energy economics and thermal performance of log houses
2- Log Home Guide (winter 1987): Why dosen't HUD analize the NBS test?
3- Log Home Guide (summer 1981): The energy economics of house construction.