Log Home Kit – Log Homes And Energy Efficiency

Residential Building

Log homes may be hand-made on-site or pre-cut in a factory for delivery to the site. Pre-cut log home kits have been produced since 1923. Log home manufacturers can also customize their designs. Wall thickness' range from 6-16 inches (152-406 millimeters [mm]). The log industry enthusiastically promotes the energy efficiency of log buildings. While there is general agreement on the aesthetic value of log homes, their energy efficiency is disputed

The conventional measure of a structure's energy efficiency is the R-value of the building material. An R-value (ft2h °F/Btu) is the rating of a material's resistance to heat flow. The R-values for logs differ according to the type of wood, ranging from about 1.41 per inch (25.4 mm) for some softwoods to 0.71 for certain hardwoods. For example, a 6-inch (152.4 mm) diameter log would rate R-8 or R-9 at best. Using conventional analysis, a wood stud wall with 3+ inches (88.9 mm) of fiberglass insulation and sheathing, siding, and wallboard rates about R-14 or R-15. On the basis of the R-value, log walls do not satisfy most building code energy standards.

The R-value rating, however, does not take into account a log's heat storage capability. Logs act as thermal mass, storing heat during the day and gradually releasing it at night. A 1982 study conducted by the National Bureau of Standards found that, in certain climates, this thermal mass effect compensated for low R-values. The thermal mass effect is most significant in milder, sunnier climates, such as the sunbelt region, where the outdoor temperature frequently moves above and below the thermostat setpoint. Some states, such as California, compute thermal mass effect and R-value together to determine building code compliance.

Several states, including Pennsylvania, Maine, and South Carolina, have exempted log-walled homes from normal energy compliance regulations. Others, such as Washington state, have approved "prescriptive packages" for various sizes of logs. The American Society of Heating, Refrigerating, and Air Conditioning Engineers 90.2 standard contains a thermal mass provision that may make it easier to get approval in other states that base their codes on this standard.

Computer simulations using thermal mass measurements and regional weather data have demonstrated compliance in states such as New York. To find out the log building code standards for your state, contact your local city or county building code officials. If your local officials are unfamiliar with log home standards, contact your state energy office. You can also contact the U. S. Department of Energy's Building Standards Hotline: (800) 270-CODE (2633)

Consulting a passive solar architect or designer may be wise, since the proper sizing of the south-facing glass is crucial to the efficient performance of a log house. (If you live in the southern hemisphere, the glazing will face north.) A concrete floor or some other heat storage material absorbs solar energy. Some designers suggest placing a masonry wall, known as a Trombe wall, directly behind the glass to increase the thermal mass effect. Adding a Trombe wall requires extensive remodeling, unless their house already has a thick, uninsulated south-facing wall. Many log home manufacturers offer solar log homes, or are able to custom-build them.

A potential problem with log homes is cold air and moisture infiltration through gaps between the logs. Manufacturers claim that kiln drying the logs prior to finish shaping and installation reduces or eliminates these gaps. They also recommend using plastic gaskets and caulking compounds to seal the walls. These seals may fail if the logs warp, shrink, or rot. The best woods to use to avoid this problem, in order of effectiveness, are cedar, spruce, pine, fir, and larch. The logs should also be seasoned for at least six months.

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About The Author:

Mark Harris is a successful author and regular contributor to http://www.home-n-house-plans.com. The best place to find new home plans, home designs & houseplans is the Internet.