As far as insulation, while log homes may have a simple R-value of 8 to 10, as compared to R-14 or more for a conventionally built framed house, testing by the National Bureau of Standards (NBS) for the Department of Housing and Urban Development (HUD) and the Department of Energy (DOE) was conducted to determine the effects of thermal mass (the bulk of solid wood log walls, or brick and block walls) on a building's energy consumption. For the test, six 20'x20' test buildings were built on the grounds of the National Bureau of Standards, 20 miles north of Washington, DC, in the fall of 1980. Each structure was identical except for construction of its exterior walls. The buildings were maintained at the same temperature levels throughout the 28-week test period between 1981 and 1982. NBS technicians precisely recorded energy consumption of each structure during this entire period.
During the three-week spring heating period, the log building used 46% less heating energy than the insulated wood frame building.
During the eleven-week summer cooling period, the log building used 24% less cooling energy than the insulated wood frame building.
During the fourteen-week winter heating period, the log building and the insulated wood frame building used virtually the same amounts of heating energy.
The National Bureau of Standards technicians conducting the test calculated the R-value of the log building, which was constructed with a 7" solid square log, at a nominal R-10. It rates the insulated wood frame building, with its 2'x4' wall and 3-1/2" of fiberglass insulation, at a nominal R-12, thus giving the wood frame structure a 17% higher R-value. Yet during the entire 28 week, three season test cycle, both buildings used virtually identical amounts of energy. This led the National Bureau of Standards to conclude that the thermal mass of log walls is an energy-conserving feature in residential construction.
Description of Test Buildings
Six 20' wide and 20' long one room test buildings with a 7-1/2" high ceiling were constructed outdoors at the National Bureau of Standards facility located in Gaithersburg, Maryland (20 miles north of Washington, DC).
Construction Details of Walls
Building #1
An insulated wood frame home, nominal R-12 (without mass) with 5/8" exterior wood siding, 2x4" stud wall, 3-1/2" fiberglass insulation, plastic vapor barrier, and 1/2" gypsum drywall.
Building #2
An un-insulated wood frame home, nominal R-4 (without mass) with same detail as above, but without the fiberglass insulation.
Building #3
An insulated masonry home, nominal R-14 (with exterior mass) with 4" brick, 4" block, 2" polystyrene insulation, plastic vapor barrier, furring strips and 1/2" gypsum drywall.
Building #4
An un-insulated masonry home, nominal R-5 (with exterior mass) with 8" block, furring strips, vapor barrier, 1/2" gypsum drywall, and no polystyrene insulation.
Building #5
A log home, nominal R-10 (with inherent mass) with 7" solid square wood logs with tongue and groove mating system, no additional insulation, no vapor barrier, and no interior drywall.
Building #6
An insulated masonry home, nominal R-12 (with interior mass) with 4" brick, 3-1/2" loose fill perlite insulation, 8" block and 1/2" interior plaster walls.
In the first extensive field testing of its kind, researchers at the Commerce Department's National Bureau of Standards (NBS) have confirmed that walls of heavyweight construction (such as those built with solid wood logs, concrete block or brick) exhibit an energy conserving "mass effect" in residential buildings during the summer and the intermediate heating season representative of fall or spring in a moderate climate. However, no mass effect was observed during the winter heating season.
According to NBS researchers, these extensive field tests should help resolve a controversy over whether residences having heavyweight walls consume less energy for space heating and cooling than buildings having lightweight walls of equivalent thermal resistance.
The National Bureau of Standards research team found that the heavyweight walls (including building number 5, the log structure) "did exhibit a thermal mass effect and thus save significant amounts of energy both in the summer cooling season and the intermediate heating season representative of fall or spring in this (Washington, DC) area."
According to NBS researchers, "the mass effect relates to the phenomenon in which heat transfer through the walls of a building is delayed by the high heat (retention) capacity of the wall mass. Consequently, the demand for heating or cooling energy to maintain indoor temperature may, under some circumstances, be pushed back until a time when wall heat transfer and equipment operating conditions are most favorable." This heat retention phenomenon is also referred to as "thermal capacitance" or time lag--the resistance of a material (such as solid wood walls) over time to allow a change in temperature to go from one side to the other.
NBS researchers explained the energy saving effect of mass during the summer cooling season this way: "In an insulated wood frame building, which is considered to have low mass, the maximum wall heat gain rate during this season is operating most often and working the hardest. In a heavy walled building (such as the log building), however, the heat transfer lag means the maximum wall heat gain rate general during the cool night period when the cooling plant is operating least often or not at all. Consequently, the cooling energy requirement is reduced."
The NBS test showed that the log structure performed better than the insulated wood building in the intermediate heating season and the summer cooling season; however, there was no appreciable difference during the winter heating season. During the winter heating season, no effect of mass was noted since all insulated buildings and the log building required comparable amounts of heating energy each hour to maintain their predetermined indoor temperatures.
As far as insects, cedar is one of the best defenses against insects because of, in the case of Western Red Cedar, it contains Thujic acid, a natural oil that acts as a natural preservative and instect barrier. Also, it's best to ensure the logs do not rest on the ground but are instead on a proper foundation. And one of the best things one can do is have the home built by an builder with lots of log building experience so the maintenance problems are minimized......for instance, an experienced builder will understand that log homes settle more over the years (from the logs drying, etc.) as they stand as compared to a standard home, and will build accordingly.