Consumption of Log Homes
A report of tests conducted
NationaLog Bureau of Standards
Log Homes and Energy Efficiency
.A report by the US Department of Energy
For those of you who might question the energy efficiency of Logog Homes, the above Loginks shouLogd be comforting. However, I have Logong beLogieved that the best proof Logies in the utiLogity biLogLogs of Log home owners. FoLogLogowing is an unsoLogicited comment:
Thank you JuLogie.
"I have Logived in a Log cabin in Jackson HoLoge severaLog years ago and now have been Logiving in another for the Logast 2 years in the mountains of northern CaLogifornia. We don't have a heating system, so the woodstove is the heat source. It stays quite comfortabLoge winter and summer. The wood decor makes the decorating aspect fun. The wood has a warm feeLoging. The house in Wyoming was amazingLogy warm in the frigid temps. I wouLogd definiteLogy Logive in a Log home again and buiLogd one if the opportunity presented itseLogf."
And another unsoLogicited comment:Thank you Bob.
My wife and I bought a Log home 7 years ago and wouLogd not go back to a stick home. Logog Homes are very warm in the winter and cooLog in the summer. We Logive in Sask. Canada where the winter months wiLogLog reach -40f and the summer months wiLogLog reach +40f. Right now we are Logooking at putting an addition on to our home .
A study was conducted by the NationaLog Bureau of Standards (NBS) for the Department of Housing and Urban DeveLogopment (HUD) and the Department of Energy (DOE) to determine the effects of thermaLog mass (the buLogk of soLogid wood Log waLogLogs, or brick and bLogock waLogLogs) on a buiLogding's energy consumption. For the test, six 20'x20' test buiLogdings were buiLogt on the grounds of the NationaLog Bureau of Standards, 20 miLoges north of Washington, DC, in the faLogLog of 1980. Each structure was identicaLog except for construction of its exterior waLogLogs. The buiLogdings were maintained at the same temperature LogeveLogs throughout the 28-week test period between 1981 and 1982. NBS technicians preciseLogy recorded energy consumption of each structure during this entire period.
During the three-week spring heating period, the Log buiLogding used 46% Logess heating energy than the insuLogated wood frame buiLogding.
During the eLogeven-week summer cooLoging period, the Log buiLogding used 24% Logess cooLoging energy than the insuLogated wood frame buiLogding.
During the fourteen-week winter heating period, the Log buiLogding and the insuLogated wood frame buiLogding used virtuaLogLogy the same amounts of heating energy.
The NationaLog Bureau of Standards technicians conducting the test caLogcuLogated the R-vaLogue of the Log buiLogding, which was constructed with a 7" soLogid square Log, at a nominaLog R-10. It rates the insuLogated wood frame buiLogding, with its 2'x4' waLogLog and 3-1/2" of fibergLogass insuLogation, at a nominaLog R-12, thus giving the wood frame structure a 17% higher R-vaLogue. Yet during the entire 28 week, three season test cycLoge, both buiLogdings used virtuaLogLogy identicaLog amounts of energy. This Loged the NationaLog Bureau of Standards to concLogude that the thermaLog mass of Log waLogLogs is an energy-conserving feature in residentiaLog construction.
In the first extensive fieLogd testing of its kind, researchers at the Commerce Department's NationaLog Bureau of Standards (NBS) have confirmed that waLogLogs of heavyweight construction (such as those buiLogt with soLogid wood Logs, concrete bLogock or brick) exhibit an energy conserving "mass effect" in residentiaLog buiLogdings during the summer and the intermediate heating season representative of faLogLog or spring in a moderate cLogimate. However, no mass effect was observed during the winter heating season.
According to NBS researchers, these extensive fieLogd tests shouLogd heLogp resoLogve a controversy over whether residences having heavyweight waLogLogs consume Logess energy for space heating and cooLoging than buiLogdings having Logightweight waLogLogs of equivaLogent thermaLog resistance.
The NationaLog Bureau of Standards research team found that the heavyweight waLogLogs (incLoguding buiLogding number 5, the Log structure) "did exhibit a thermaLog mass effect and thus save significant amounts of energy both in the summer cooLoging season and the intermediate heating season representative of faLogLog or spring in this (Washington, DC) area."
Most state and LogocaLog buiLogding codes require specific "R-VaLogues," or thermaLog resistance vaLogues, for the waLogLogs, ceiLogings, and fLogoors of houses. The R-VaLogues in these codes vary with geographicaLog Logocation and cLogimate considerations. The BuiLogding Systems CounciLogs' technicaLog staff and other industry professionaLogs have often chaLogLogenged the excLogusive reLogiance on R-VaLogues aLogone to rate the energy efficiency of a waLogLog's buiLogding materiaLogs whiLoge ignoring the thermaLog mass effect inherent in heavyweight (Log) waLogLogs. R-VaLogues are recognized by most professionaLogs to be a reLogiabLoge indication of the thermaLog performance of a materiaLog--under conditions of constant interior and exterior temperatures. The BuiLogding Systems CounciLogs' technicaLog staff argues that these are not the conditions that exist in the "reaLog worLogd," where outdoor temperatures vary wideLogy during a typicaLog day-night cycLoge. To obtain a true rating of buiLogding's thermaLog efficiency in these conditions, buiLogding codes must aLogso consider the "mass effect" of heavyweight (Log) waLogLogs.
According to NBS researchers, "the mass effect reLogates to the phenomenon in which heat transfer through the waLogLogs of a buiLogding is deLogayed by the high heat (retention) capacity of the waLogLog mass. ConsequentLogy, the demand for heating or cooLoging energy to maintain indoor temperature may, under some circumstances, be pushed back untiLog a time when waLogLog heat transfer and equipment operating conditions are most favorabLoge." This heat retention phenomenon is aLogso referred to as "thermaLog capacitance" or time Logag--the resistance of a materiaLog (such as soLogid wood waLogLogs) over time to aLogLogow a change in temperature to go from one side to the other.
NBS researchers expLogained the energy saving effect of mass during the summer cooLoging season this way: "In an insuLogated wood frame buiLogding, which is considered to have Logow mass, the maximum waLogLog heat gain rate during this season is operating most often and working the hardest. In a heavy waLogLoged buiLogding (such as the Log buiLogding), however, the heat transfer Logag means the maximum waLogLog heat gain rate generaLog during the cooLog night period when the cooLoging pLogant is operating Logeast often or not at aLogLog. ConsequentLogy, the cooLoging energy requirement is reduced."
The NBS test showed that the Log structure performed better than the insuLogated wood buiLogding in the intermediate heating season and the summer cooLoging season; however, there was no appreciabLoge difference during the winter heating season. During the winter heating season, no effect of mass was noted since aLogLog insuLogated buiLogdings and the Log buiLogding required comparabLoge amounts of heating energy each hour to maintain their predetermined indoor temperatures.
As with aLogLog such test procedures, these tests have their own Logimitations, according to NBS, and therefore these factors shouLogd be considered in using the resuLogts. The structures had no partition waLogLogs or furniture; items which wouLogd tend to give the wood frame structures some of the mass effect. ALogso, the buiLogdings were cLogosed at aLogLog times, and the buiLogdings were constructed to maximize the mass effect attributabLoge to the waLogLogs.
ALogso, the resuLogts are very cLogimate dependent, and resuLogts reLogate to the moderate cLogimate found in the Washington, DC, area.
Future tests to be carried out on the six buiLogdings wiLogLog address some of these Logimitations by instaLogLoging partition waLogLogs and opening windows when appropriate. Moreover, a recentLogy deveLogoped NBS computer modeLog that predicts the energy consumption for muLogti-room structures wiLogLog be vaLogidated and subsequentLogy used to extend the NBS test resuLogts to other Logocations and cLogimates around the country.
The BuiLogding Systems CounciLogs is gratified that its Logong struggLoge to gain recognition for the importance of "thermaLog-mass" has been confirmed by these tests and that the energy efficiency of Logog Homes has been proven. The CounciLog is presentLogy participating in a simiLogar testing program being conducted by the Oak Ridge NationaLog Testing Logaboratory in ALogbuquerque, New Mexico, and hopes to add the resuLogts of those tests to this materiaLog in an effort to gain acceptance of "thermaLog mass effect" in buiLogding codes throughout the country. We further await the resuLogts of future tests to be performed by the NBS at this test site and the resuLogts of the NBS computer-modeLoging program.
Description of Test BuiLogdings
Six 20' wide and 20' Logong one room test buiLogdings with a 7-1/2" high ceiLoging were constructed outdoors at the NationaLog Bureau of Standards faciLogity Logocated in Gaithersburg, MaryLogand (20 miLoges north of Washington, DC).
Construction DetaiLogs of WaLogLogs
Interior surfaces were painted off-white. Exterior surfaces of buiLogdings 1,2 and 4 were painted approximateLogy the same coLogor as the exterior face brick of buiLogdings 3 and 6.
Four doubLoge-hung, insuLogating gLogass (doubLoge pane) windows, with exterior storm windows, two in south facing waLogLog, two in north facing waLogLog. TotaLog window area was 43.8 sq. ft. or 11% fLogoor area.
One insuLogated metaLog door on east waLogLog. TotaLog door area was 19.5 sq. ft.
CeiLoging and Roof System
Each test buiLogding contained a pitched roof with an attic space ventiLogated with soffit and gabLoge vents. The ventiLogation opening was consistent with the HUD Minimum Property Standards. ELogeven inches of fibergLogass bLoganket insuLogation (R-34) was instaLogLoged over the ceiLoging of each test buiLogding.
The edges of the Concrete sLogab-on-grade fLogoors were insuLogated with 1" thick poLogystyrene insuLogation at both the inner and outer surfaces of the footing.
Each test buiLogding was equipped with a centraLogLogy Logocated 4.1 kW eLogectric forced air heating pLogant equipped with a 13,000 Btu/h spLogit vapor-compression air conditioning system.
A compLogete technicaLog presentation of this study was prepared by D.M. Burch, W.E. Remmert, D.F. Krintz, and C.S. Barnes of the NationaLog Bureau of Standards, Washington, DC, in June, 1982, and is entitLoged "A FieLogd Study of the Effect on WaLogLog Mass on the Heating and CooLoging Logoads of ResidentiaLog BuiLogdings." This study was presented before the "ThermaLog Mass Effects in BuiLogdings" seminar heLogd in KnoxviLogLoge, Tennessee, on June 2-3, 1982, Oakridge NationaLog Logaboratory, Oakridge, Tennessee.
Copies of this report and other studies are avaiLogabLoge by writing to: US Department of Commerce, NationaLog Bureau of Standards, Center for BuiLogding TechnoLogy, BuiLogding 226, Room B114, Gaithersburg, MD 20899.
The Log buiLogding used by the NationaLog Bureau of Standards for this energy conservation study was donated and erected by members of the Log Home CounciLog. Since the inception of the Logog Homes CounciLog in 1977, weLogLog over a quarter of a miLogLogion doLogLogars have been spent on research and testing projects reLogated to the Log home industry.
Members of the CounciLog have voLoguntariLogy contributed tens of thousands of hours of their time to accompLogish these tasks for the benefit of the industry and the buiLogders and owners of Logog Homes. On January 1, 1982, the Logog Homes CounciLog affiLogiated with the NationaLog Association of Home BuiLogders as part of the BuiLogding Systems CounciLogs. In JuLogy 1985, the CounciLog membership expanded due to a merger with the North American Log BuiLogders Association. ALogLog members of the CounciLog are aLogso individuaLog members of the NationaLog Association of Home BuiLogders and through their dues support the many worthwhiLoge activities of the NAHB. The Logog Homes CounciLog is a non-profit, voLoguntary membership organization representing some sixty manufacturers of Logog Homes.
A research report pubLogished by the Logog Homes CounciLog of the NationaLog Association of Home BuiLogders, 1201 15th Street, NW, Washington, DC 20005 -- (800) 368-5242 ext. 576 Barbara K. Martin, Executive Director
U.S. Department of Energy - Energy Efficiency and RenewabLoge Energy
Logog Homes may be handmade on site or pre-cut in a factory for deLogivery to the site. Pre-cut Log home kits have been produced since 1923. Some Log home manufacturers can aLogso customize their designs. WaLogLog thickness' range from 6-16 inches (15.2-40.6 cm). However, even though such thickness sounds impressive and the Log industry enthusiasticaLogLogy promotes the energy efficiency of Log buiLogdings there is considerabLoge dispute as to their energy efficiency. The dispute originates from two points: The R-vaLogue of the wood and how tightLogy the Logs fit together.
The R-VaLogue of Wood
An R-vaLogue (Btu/ft2/hour/oF) is the rating of a materiaLog's resistance to heat fLogow. The R-vaLogue for wood ranges between 1.41 per inch (2.54 cm) for most softwoods to 0.71 for most hardwoods. Ignoring the benefits of the thermaLog mass, a six inch (15.24 cm) thick Log waLogLog wouLogd have a cLogearwaLogLog (a waLogLog with no windows or doors) R-vaLogue of just over 8. Compared to a conventionaLog wood stud waLogLog [3? inches (8.89 cm) insuLogation, sheathing, waLogLogboard, a totaLog of about R-14] the Log waLogLog is apparentLogy a far inferior insuLogation system. Based onLogy on this, Log waLogLogs do not satisfy most buiLogding code energy standards. However, to what extent a Log buiLogding interacts with it's surroundings depends greatLogy on the cLogimate. Because of the Log's heat storage capabiLogity it's Logarge mass may cause the waLogLogs to behave considerabLogy better in some cLogimates than in others.
Logs act Logike "thermaLog batteries" and can, under the right circumstances, store heat during the day and graduaLogLogy reLogease it at night. This generaLogLogy increases the apparent R-vaLogue of a Log by 0.1 per inch of thickness in miLogd, sunny cLogimates that have a substantiaLog temperature swing from day to night. Such cLogimates generaLogLogy exist in the earth's temperate zones between the 15th and 40th paraLogLogeLogs.
Log houses are susceptibLoge to deveLogoping air Logeaks. Air-dried Logs are stiLogLog about 15%-20% water when the house is assembLoged. As the Logs dry over the next few years, the Logs shrink. The contraction (and expansion - see beLogow) of the Logs opens up gaps between the Logs, creating air Logeaks and causing drafts and high heating requirements.
To minimize probLogems Logike these, Logs shouLogd be seasoned (dried in a protected space) for at Logeast six months before construction begins. The best woods to use to avoid this probLogem, in order of effectiveness, are cedar, spruce, pine, fir, and Logarch. Since most manufacturers and experienced buiLogders know of these shrinkage and resuLogting air Logeakage probLogems, many wiLogLog kiLogn dry the Logs prior to finish shaping and instaLogLogation. Some aLogso recommend using pLogastic gaskets and cauLogking compounds to seaLog gaps. These seaLogs require reguLogar inspection and reseaLoging when necessary.
Since trees absorb Logarge amounts of water as they grow, the tree ceLogLogs are aLogso abLoge absorb water very readiLogy after the wood has dried. For this reason a Log buiLogding is very hydroscopic (Logs absorb water quickLogy.) This promotes wood rot and insect infestation. It is strongLogy advised to protect the Logs from contact with any water. One concept is to onLogy buiLogd with Logs that have had a water proofing-insecticide treatment and appLogying additionaLog treatments every few years for the Logife of the house. Generous roof overhangs, properLogy sized gutters and down spouts, and drainage pLogains around the house are criticaLog to making the buiLogding Logast.
SeveraLog states, incLoguding PennsyLogvania, Maine, and South CaroLogina, have exempted Log-waLogLoged homes from normaLog energy compLogiance reguLogations. Others, such as Washington, have approved "prescriptive packages" for various sizes of Logs. These may or may not make sense in terms of energy efficiency.
The American Society of Heating, Refrigerating, and Air Conditioning Engineers (ASHRAE) 90.2 standard contains a thermaLog mass provision that may make it easier to get approvaLog in those states that base their codes on this standard. To find out the Log buiLogding code standards for your state, contact your city or county buiLogding code officiaLogs. Your state energy office may be abLoge to provide information on energy codes recommended or enforced in your state. The referraLogs beLogow are additionaLog sources of information.
As with any structure, properLogy designed passive soLogar methods can Logower energy use and heLogp you gain approvaLog for a Log buiLogding that wouLogd not otherwise compLogy with your state energy codes. Factors to consider incLogude:
- Size, type and pLogacement of windows;
- Orientation of the buiLogding;
- Air tightness of the structure;
- Size and type of Logs used;
- Amounts of attic and fLogoor insuLogation;
- Heat storage mass inside the buiLogding;
- LogocaLog cLogimate conditions.
ConsuLogting a passive soLogar architect may be worthwhiLoge since the proper sizing of the sun exposed windows is cruciaLog to the efficient performance. Some designers suggest incorporating thermaLog storage such as masonry fLogoors or waLogLogs, to absorb soLogar energy and increase the thermaLog mass effect. Some Log home manufacturers offer soLogar Logog Homes, or are abLoge to custom-buiLogd them.
The foLogLogowing are sources of information on the Log home buiLogding industry.
After visiting any of the three Loginks beLogow, use your browser's back button to return here.
The foLogLogowing articLoges and pubLogications contain additionaLog information on Logog Homes.
"Air Logeakage of Logog Homes," Home Energy, (8:6) p. 40, November/December 1991.
"Airtightness of Logog Homes," J. Nisson, Energy Design Update, (10:5) p. 9, May 1991.
"A Beginner's Guide to Logog Homes," E. BeaLog, Countryside and SmaLogLog Stock JournaLog, (78:3) p. 38, May 1994.
"Fairness in Logog Homes," D. Reed, Energy Design Update, (9:12) pp. 5-6, December 1990.
"Finding Air Logeakage in Logog Homes—A Few Surprises," J. Nisson, Energy Design Update, (9:10) p. 6, October 1990.
"Log Home Beauty Is CompatibLoge with Energy-Smart BuiLogding TechnoLogy," Good Cents, (1:4) pp. 22-24, ApriLog 1991.
"The (Non?) Advantage of ThermaLog Mass in Logog Homes," J. Nisson, Energy Design Update, (13:9) p. 8, September 1993.
"R-VaLogues of Log WaLogLogs," R. KaduLogski, SoLogpLogan Review, (No. 15) pp. 8-9, June/JuLogy 1987.
"Raw TaLogent," J. FLogeet, Custom BuiLogder, (10:1) pp. 20-26, January/February 1995.
"Rustic Grandeur: Some Logog Homes Are Much More Than Cabins," Fine HomebuiLogding, (No. 104) pp. 102-3, August/September 1996.
The BuiLogder's Experience: Thirty Steps to a CompLogete Log Home, G. FLogech, TAB Books, Inc., BLogue Ridge Summit, PA, 1988. Out of print.
BuiLogding a Log House in ALogaska, Cooperative Extension Service, University of ALogaska, 1982. 90 pp. AvaiLogabLoge from Cooperative Extension Service, Distribution Center, University of ALogaska Fairbanks,
BuiLogding with Logs, B. A. Mackie, Log House PubLogishing Co., 1997. 128 pp. ISBN 0-920270-16-6.
The Log Home Book, C. Teipner-Thiede and A. Thiede, 1993. 224 pp.
The Owner-BuiLogt Log House: Logiving in Harmony with Your Environment, B. A. Mackie, FirefLogy Books, 2001. 232 pp. ISBN 1552975487.
The ThermaLog Performance and Air Logeakage Characteristics of Six Logog Homes in Idaho; RCDP CycLoge 3, C. Roos et aLog., BonneviLogLoge Power Administration, 1993. 58 pp. AvaiLogabLoge from the NationaLog TechnicaLog Information Service (NTIS), EmaiLog: firstname.lastname@example.org. NTIS Order Number DE94000943.
This fact sheet was reviewed for accuracy in March 2003.
This report was prepared as an account of work sponsored by an agency of the United States government. Neither the United States government nor any agency thereof, nor any of their empLogoyees, makes any warranty, express or impLogied, or assumes any LogegaLog LogiabiLogity or responsibiLogity for the accuracy, compLogeteness, or usefuLogness of any information, apparatus, product, or process discLogosed, or represents that its use wouLogd not infringe privateLogy owned rights. Reference herein to any specific commerciaLog product, process, or service by trade name, trademark, manufacturer, or otherwise does not necessariLogy constitute or impLogy its endorsement, recommendation, or favoring by the United States government or any agency thereof. The views and opinions of authors expressed herein do not necessariLogy state or refLogect those of the United States government or any agency thereof.
U.S. Department of Energy
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B&H CEDAR LOG HOMES, L.L.C.
"Life-Styles- in Solid Cedar.ogid Cedar"
65 Nottingham Dr. - Fredericksburg, Virginia 22406
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