R-Values, Thermal Mass, & Wall Mass Effect on the Energy Costs of Homes: the Log Home Report InspectAPedia® -
R-Values of Log Homes & Solid Log Walls
Thermal Wall Mass Study in Log, Masonry, & Wood Frame Homes, 1982
Energy Efficiency of Log Homes
Effects of solid log construction thermal mass on log home heating and cooling costs
Field Study of the Effect on Wall Mass on the Heating and Cooling Loads of Residential Buildings
Questions & answers about the R-values and heating or cooling characteristics of log construction: log home energy efficiency, thermal mass, and the effects of thermal mass on heating and cooling costs.
This article explains the effects of log home thermal mass on heating and cooling costs. We give R-values for solid log walls, we compare solid log walls to log-slab-sided wood frame wall construction, and we cite expert research on thermal mass in log-constructed buildings.
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This series of articles provides information on the heating & cooling characteristics of solid log home construction. We include illustrations of log structures from several very different areas and climates in both the United States and Norway. Our page top photo shows a modern solid log home in Pennsylvania.
Heating, Cooling, and Insulation R-Values & Characteristics of Log Homes
R-Values for wooden log walls given by the U.S. DOE are in error except for square log walls. D-logs and round logs that are given a nominal log thickness, say 6" logs are calculated by DOE as having an R-value of just over 8. This is incorrect for non-square logs because the cross section of the log is 6" only at the log's widest point.
A correct assessment of the R-value of a wooden log wall needs to be calculated based on the average wall thickness, considering the variation in thicknesses over the curvature of the logs. Therefore the DOE's value is on the "high" end of the R-value of a log wall.
Slab-sided log homes that use conventional stud framing for walls will have about the same R-value as other wood-framed buildings of similar construction, plus the added value of the average thickness of the slab siding.
Air leaks in log homes (or in any home) will have a significant, possibly dominant effect on the home's heating and cooling costs. See Minimizing Air Leakage in Log Homes.
Log Home Thermal Mass Effects on Heating, Cooling, & Comfort
Our photo (left) shows an older solid-log home in Pennsylvania under winter conditions. Notice the absence of snow on the roof and the large icicles? Where is the most heat loss in this log home? What are the effects of the thermal mass of this solid log home on its heating (or summer cooling) costs?
The effects on heating efficiency and costs of the thermal mass of log walls on a solid log home not a new question, though the debate continues.
A widely-cited study of interest to log home owners and builders studying the energy characteristics of log buildings was completed in 1982: A Field Study of the Effect on Wall Mass on the Heating and Cooling Loads of Residential Buildings, D.M. Burch, W.E. Remmert, D.F. Krintz,
and C.S. Barnes,
National Bureau of Standards. The study was undertaken in response to rising energy costs and an ongoing search for ways to improve building energy efficiency in the 1980's - conditions that are appropriate in today's climate of rising energy costs as well. The study also was undertaken to test the results of non-empirical computer modeling of the effects of thermal mass on building energy consumption. Those computer modeling results had indicated that the effects of thermal mass on energy consumption would be small. From the document abstract:
Six test buildings were extensively instrumented for measuring heating and cooling loads, wall heat transmission, and indoor temperature and humidity. During these measurements, the effect of wall mass on heating and cooling loads was observed. these buildings were exposed to a winter heating season, an intermediate heating season, and a summer cooling season.
The test buildings were 20 x 20 ft. (6.1 x 6.1 m) one room buildings constructed at Gaithersburg, MD. These buildings had the same floor plan and orientation. They were identical, except for the wall construction, which was as follows: insulated lightweight wood frame; un insulated lightweight wood frame; insulated masonry with outside mass; uninsulated masonry; log; and insulated masonry with inside mass;. The insulated buildings, including the log building were designed to have walls of approximately equivalent steady-state thermal resistance; the uninsulated buildings were also designed to have walls of approximately equivalent steady-state thermal resistance.
No reductions in heating energy attributable to wall mass were observed during the winter heating season, when the buildings typically did not float (i.e. some energy was applied each hour). However, during the intermediate heating season and the summer heating season, when the buildings floated during a portion of the day (i.e. no heating or cooling load occurred during a portion of the day and the indoor temperature rose above, or fell below the indoor set temperature), significant reductions in load attributable to wall mass were observed. Wall mass was observed to have a larger effect when it was placed inside the wall insulation as opposed to outside the wall insulation.
The two bar graphs below, also from this study, show the effects of thermal mass on the test chamber intermediate heating and summer cooling season loads. Buildings 1-6 are listed left-to-right in these charts in order 1, 3, 5, 6, 2, 4 and are identified as:
insulated lightweight wood frame wall structure
un insulated lightweight wood frame wall structure
insulated masonry wall with outside mass
uninsulated masonry wall
log wall construction
insulated masonry wall with inside mass
As we point out at Warnings below, readers should not assume that these results translate directly to a real home with interior partitions and furnishings.
Energy consumption for residential space heating and space cooling represents about 12 percent of the total energy required in the United states. With the advent of fuel shortages which have produced spiraling energy costs, much attention has been focused on strategies for reducing energy consumption in residential buildings. A strategy, which is the subject of this paper, deals with the effect of wall mass on the heating and cooling loads of residential buildings.
The effect of wall mass may be illustrated by considering a residential building exposed to an outdoor condition for which the outdoor temperature approaches the balance point (float zone) for the building. If the heating/cooling plant is turned off, the indoor temperature will fluctuate in response to the outdoor diurnal temperature variation. The building envelope will provide a reduction in the amplitude of the diurnal outdoor temperature wave form.
What this means in less scientific language is that in an amount that varies depending on their thermal mass, the walls of a home, such as a log home or a solid masonry home, will reduce the extent of temperature swings inside the building during intermediate heating seasons and during the cooling season. Another way to view this observation is that energy is stored in the thermal mass of the walls and returned to the interior as heat during the intermediate heating season, or during the cooling season, the thermal mass of walls may absorb some interior heat, cooling the building interior. At least, for a while.
The 1982 thermal mass study continues to point out that
... the amplitude reduction will be considerably greater for the masonry [or solid log] residence than for the wood-frame residence, owing to the large heat capacity of the masonry [or log] material. Therefore, if high and low thermostat set points are established for space cooling and space heating, the masonry [or log] building will have considerably smaller indoor temperature excursions above and below the high and low set points, thereby causing its heating and cooling energy [consumption] to be smaller than that for the wood-frame residence.
Warnings about The Log Home Report Conclusions
The authors conducting this Field Study of the Effect on Wall Mass on the Heating and Cooling Loads of Residential Buildings ("The Log Home Report") included careful consideration of the effects of solar gain, air infiltration or exfiltration, and similar considerations that would otherwise have confounded the study results, especially when comparing such different building wall construction methods as wood frame, masonry, and solid logs.
And sound mathematical techniques and instrumentation were used in the study methodology. But the study results do not translate directly to actual furnished residential structures, as the authors explained in some cautionary notices:
Watch out: The study, referred to by some sources as "the Log Home Report" also includes important cautions that should not be ignored:
The effect of thermal wall mass has been shown to be climate dependent. [Study references 1, 2, 3, and 5]. Therefore, the test results of the [1982] study should not be directly extended to other climates.
Perhaps it is equally important is the fact that the test results should not be extended to a real house situation for the following reasons.
The test buildings were one-room test cells which did not contain interior partition walls and interior furnishings. The addition of interior partition walls and interior furnishings would have added considerable interior mass which would have affected the observed results; and
Heat transmission through the walls of the test buildings was a larger part of the overall envelope heat transfer compared to a typical house due to high thermal; resistance in other components of the building envelopes (i.e. the ceilings contained R-34 (R-6.0 m2.K/W) glass-fiber insulation, the windows contained triple-glazing, the floor slabs were insulated over the top with R-11.2 (R-1.97 m2.K/W) polystyrene insulation, and the air infiltration rates were quite small.
We interpret the study and the author's cautions to mean that while there is an effect of building thermal mass on building heating or cooling loads during some seasons (intermediate heating season and summer cooling season), the actual effects of thermal wall mass likely to be observed in a real, furnished, residential structure, will be different, and possibly significantly less for normal buildings.
OPINION: the benefits of increased thermal mass on building energy costs has been discussed and is demonstrated in energy-efficient building designs such as passive solar heating, but to state the portion of energy savings attributed to thermal wall mass alone in all structures requires careful study.
Questions & answers about the R-values and heating or cooling characteristics of log construction: log home energy efficiency, thermal mass, and the effects of thermal mass on heating and cooling costs.
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"The Logless Log Home," Jim Robbins, New York Times, 05/05/2010 Home section, p. D1 & D6.
"Shop Talk," Martin Mintz, AIA, Builder Magazine, April 1986, detailed solutions for log shrinkage movement by using a "T" jamb at windows and doors. A January 1986 Builder Magazine article shows window installation details in 8" thick log walls.
"Caulking, Chinking, Insulators, Sealants - which System works Best," Log Home and Alternative Housing Builder, Nov-Dec 1983.
Lincoln Log Homes Marketing, Inc., 6000 Lumber Lane, Kannapolis NC 28081 704-932-6151
Insulating Characteristics of log homes were neatly summarized by Roger Rawlings in "Log Homes in a New Light," Rodale's New Shelter, April 1983, p. 28
Merrimac Log Homes, Henniker, NH, sells log home products, milled log home kits, log siding, and log home plans and log home construction accessories. 866-637-7462 or logs@mlhnh.com - merrimacloghomes.com
PermaChink Systems, Knoxville TN 800-548-1231 provides a range of log chinking products, coatings, and sealants for log and other wood buildings.
Krigger, J.; Dorsi, C. (2004). Residential Energy: Cost Savings and Comfort for Existing Buildings. Helena, MT: Saturn Resource Management.
"Log Home Design", U.S. Department of Energy guide to log homes and energy savings
(at www.energysavers.gov/your_home/designing_remodeling/index.cfm/mytopic=10350 ) includes these interesting sub-sections:
"Weather-Resistive Barriers [copy on file as /interiors/Weather_Resistant_Barriers_DOE.pdf ] - ", how to select and install housewrap and other types of weather resistive barriers, U.S. DOE
A Field Study of the Effect on Wall Mass on the Heating and Cooling Loads of Residential Buildings. (local copy), D.M. Burch, W.E. Remmert, D.F. Krintz,
and C.S. Barnes,
National Bureau of Standards,
Washington, D.C. 20234, Proceedings of the Building Thermal Mass Seminar,
Knoxville, TN; 6/2-3/82,
Oak Ridge National Laboratory
Oak Ridge, TN,
- available from U.S. Department of Commerce, National Bureau of Standards, Center for Building Technology, Building 226, Room Bl 14, Gaithersburg, MD 20899.
original source - http://fire.nist.gov/bfrlpubs/build82/PDF/b82001.pdf
This study was presented before the "Thermal Mass Effects in Buildings" seminar held in Knoxville, Tennessee, on June 2-3, 1982, Oakridge National Laboratory, Oakridge, Tennessee.
"Whole-House Systems Approach [to saving on energy costs]", U.S. DOE, describes designing and constructing an energy-efficient home by considering all of the house systems. Original DOE source: www.energysavers.gov/your_home/designing_remodeling/index.cfm/mytopic=10370
"Insulation and Air Sealing", U.S. DOE describes how to reduce a home's heating and cooling costs by proper insulation and air leak sealing. Moisture control and ventilation are also discussed.
"Lighting and Daylighting", U.S. DOE, is a very brief DOE article suggesting how to reduce the cost of lighting in a building
"Space Heating and Cooling", U.S. DOE, attacks the biggest energy user in buildings, typically about 56% of energy use in a typical home in the United States.
"Water Heating", U.S. DOE, addresses reducing the cost of heating domestic hot water used for washing and bathing - that accounts for 14-25% of home energy usage in the U.S. and includes
"Energy Efficient Water Heating", U.S. DOE includes suggestions to lower hot water heating costs including reducing hot water usage, lowering hot water temperature, insulating the water tank (nonsense), insulating hot water pipes, installing heat traps on the water heater tank, water heater timers, and drain-water heat recovery systems (possibly not cost effective)
Books & Articles on Building & Environmental Inspection, Testing, Diagnosis, & Repair
Our recommended books about building & mechanical systems design, inspection, problem diagnosis, and repair, and about indoor environment and IAQ testing, diagnosis, and cleanup are at the InspectAPedia Bookstore. Also see our Book Reviews - InspectAPedia.
The Home Reference Book - the Encyclopedia of Homes, Carson Dunlop & Associates, Toronto, Ontario, 2010, $69.00 U.S., is available from Carson Dunlop, and from the InspectAPedia bookstore. The 2010 edition of the Home Reference Book is a bound volume of more than 450 illustrated pages that assist home inspectors and home owners in the inspection and detection of problems on buildings. The text is intended as a reference guide to help building owners operate and maintain their home effectively. InspectAPedia.com ® author/editor Daniel Friedman is a contributing author. Field inspection worksheets are included at the back of the volume.
Design of Wood Structures - ASD, Donald E. Breyer, Kenneth Fridley, Kelly Cobeen, David Pollock, McGraw Hill, 2003, ISBN-10: 0071379320, ISBN-13: 978-0071379328
This book is an update of a long-established text dating from at least 1988 (DJF); Quoting: This book is gives a good grasp of seismic design for wood structures. Many of the examples especially near the end are good practice for the California PE Special Seismic Exam design questions. It gives a good grasp of how seismic forces move through a building and how to calculate those forces at various locations.THE CLASSIC TEXT ON WOOD DESIGN UPDATED TO INCLUDE THE LATEST CODES AND DATA. Reflects the most recent provisions of the 2003 International Building Code and 2001 National Design Specification for Wood Construction. Continuing the sterling standard set by earlier editions, this indispensable reference clearly explains the best wood design techniques for the safe handling of gravity and lateral loads. Carefully revised and updated to include the new 2003 International Building Code, ASCE 7-02 Minimum Design Loads for Buildings and Other Structures, the 2001 National Design Specification for Wood Construction, and the most recent Allowable Stress Design.
Diagnosing & Repairing House Structure Problems, Edgar O. Seaquist, McGraw Hill, 1980 ISBN 0-07-056013-7 (obsolete, incomplete, missing most diagnosis steps, but very good reading; out of print but used copies are available at Amazon.com, and reprints are available from some inspection tool suppliers). Ed Seaquist was among the first speakers invited to a series of educational conferences organized by D Friedman for ASHI, the American Society of Home Inspectors, where the topic of inspecting the in-service condition of building structures was first addressed.
Defects and Deterioration in Buildings: A Practical Guide to the Science and Technology of Material Failure, Barry Richardson, Spon Press; 2d Ed (2001), ISBN-10: 041925210X, ISBN-13: 978-0419252108. Quoting: A professional reference designed to assist surveyors, engineers, architects and contractors in diagnosing existing problems and avoiding them in new buildings. Fully revised and updated, this edition, in new clearer format, covers developments in building defects, and problems such as sick building syndrome. Well liked for its mixture of theory and practice the new edition will complement Hinks and Cook's student textbook on defects at the practitioner level.
"Avoiding Foundation Failures," Robert Marshall, Journal of Light Construction, July, 1996 (Highly recommend this article-DF)
"A Foundation for Unstable Soils," Harris Hyman, P.E., Journal of Light Construction, May 1995
"Backfilling Basics," Buck Bartley, Journal of Light Construction, October 1994
"Inspecting Block Foundations," Donald V. Cohen, P.E., ASHI Reporter, December 1998. This article in turn cites the Fine Homebuilding article noted below.
"When Block Foundations go Bad," Fine Homebuilding, June/July 1998
Masonry structures: The Masonry House, Home Inspection of a Masonry Building & Systems, Stephen Showalter (director, actor), DVD, Quoting: Movie Guide Experienced home inspectors and new home inspectors alike are sure to learn invaluable tips in this release designed to take viewers step-by-step through the home inspection process. In addition to being the former president of the National Association of Home Inspectors (NAHI), a longstanding member of the NAHI, the American Society of Home Inspectors (ASHI), and the Environmental Standard Organization (IESO), host Stephen Showalter has performed over 8000 building inspections - including environmental assessments. Now, the founder of a national home inspection school and inspection training curriculum shares his extensive experience in the inspection industry with everyday viewers looking to learn more about the process of evaluating homes. Topics covered in this release include: evaluation of masonry walls; detection of spalling from rebar failure; inspection of air conditioning systems; grounds and landscaping; electric systems and panel; plumbing supply and distribution; plumbing fixtures; electric furnaces; appliances; evaluation of electric water heaters; and safety techniques. Jason Buchanan --Jason Buchanan, All Movie Review
Masonry Structures: Behavior and Design, Robert G. Drysdale, Ahmid A. Hamid, Lawrie R. Baker, The Masonry Society; 2nd edition (1999), ISBN-10: 1929081014, ISBN-13: 978-1929081011
Straw Bale Home Design, U.S. Department of Energy provides information on strawbale home construction - original source at http://www.energysavers.gov/your_home/designing_remodeling/index.cfm/mytopic=10350
More Straw Bale Building: A Complete Guide to Designing and Building with Straw (Mother Earth News Wiser Living Series), Chris Magwood, Peter Mack, New Society Publishers (February 1, 2005), ISBN-10: 0865715181 ISBN-13: 978-0865715189 - Quoting: Straw bale houses are easy to build, affordable, super energy efficient, environmentally friendly, attractive, and can be designed to match the builder’s personal space needs, esthetics and budget. Despite mushrooming interest in the technique, however, most straw bale books focus on “selling” the dream of straw bale building, but don’t adequately address the most critical issues faced by bale house builders. Moreover, since many developments in this field are recent, few books are completely up to date with the latest techniques. More Straw Bale Building is designed to fill this gap. A completely rewritten edition of the 20,000-copy best--selling original, it leads the potential builder through the entire process of building a bale structure, tackling all the practical issues: finding and choosing bales; developing sound building plans; roofing; electrical, plumbing, and heating systems; building code compliance; and special concerns for builders in northern climates.
Lincoln Log Homes Marketing, Inc., 6000 Lumber Lane, Kannapolis NC 28081 704-932-6151
Merrimac Log Homes, Henniker, NH, sells log home products, milled log home kits, log siding, and log home plans and log home construction accessories. 866-637-7462 or logs@mlhnh.com - merrimacloghomes.com
PermaChink Systems, Knoxville TN 800-548-1231 provides a range of log chinking products, coatings, and sealants for log and other wood buildings.
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