Home Buyers/Owners Guide to the Insulating Value (R-Value) & Heating Comfort of Log Homes

INSULATION R-VALUE, SOLID LOG WALL - Log home insulating and R-value properties
- What is the energy efficiency of solid log homes compared with conventional wood-framed structures?
- Comparison of the insulating and thermal properties of solid log homes with other structures
Questions & Answers about the insulating, heating, and cooling properties and comfort of log homes and other solid wood log-constructed buildings
References

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This article explains the insulating and heating properties of log homes, comparing solid log structures, slab-sided log homes, and conventionally framed homes.

This series of log home construction and maintenance articles provides information on the inspection and diagnosis of damage to new and older log homes and includes description of log house and log siding insulation values and alternatives, and also a description of the characteristics of slab-sided log homes as well as all other types of 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 kit log home constructed in New York State. For modern kit and factory-sourced log structures we include details of common construction and building defects that cause water and air leaks and ultimately rot damage and we point to key problem areas that need to be inspected carefully when buying or maintaining a log home.

Readers should see R-VALUES & THERMAL MASS in LOG HOMES, also see Energy Efficiency of Log Homes where we introduce the R-value of solid wood, log home air leaks, and the thermal mass of log homes. Readers whose homes are drafty, leaky, or otherwise too cold and who have high heating bills should also see these air leak articles: AIR BYPASS LEAKS, AIR LEAK DETECTION TOOLS, AIR LEAK MINIMIZATION, and AIR SEALING STRATEGIES.

A Comparison of the Insulation Value of a Solid Log Home to a Conventionally Framed Home

A 6-inch fiberglass frame wall has an "R" value of about R-19 while a 6" log solid wood wall has an "R" value of about 1 per inch or about R-6 in insulating value.

When a solid log wall is built using logs rounded on one or both exposed sides, the nominal log diameter does not give an accurate estimate of the wall's insulating value.

That is because portions of the wall are constructed at a thickness less than the full log's diameter.

The average wall thickness should be used to calculate the "R" value of a solid log wall when rounded logs are used.

The beautiful log cabin in our photo (above left), located on Elk Lake in Michigan, was built more than 50 years ago as a summer retreat. While thick native logs were used in its construction, this cabin is not comfortably habitable in the dead of winter, principally due to drafts, leaky windows, and thin upper walls.

Lighting the huge stone fireplace and burning wood continuously provides comfort to Lon (photo at left) who is sitting around the fire, while the same fire's draft draws freezing air into the rest of the structure.

The average wall thickness over the entire log wall area of this cabin is about 5" - R-5 in terms of resistance to heat loss. When we consider that the upper portion of this cabin is sheathed with 3/4" lumber, and the roof is un insulated, the average R-value of this beautiful, but chilly structure is about R-2 over its entire surface area.

But a tight, non-drafty solid log home will have tremendous thermal mass and can be very comfortable and easily heated, as we discuss below. It's not accurate to compare an antique (and drafty) log cabin such as the one above with a a modern log home nor with a conventional wood-framed and insulated structure. Modern milled-log homes that are properly constructed are quite comfortable in cold weather.

Thermal Mass & R-Values of Solid Log Homes Compared with Insulated Wall Wood Structures

A second error (after draftiness) that plagues comparison of the relative comfort and heating efficiency of different types of homes is the failure to consider all of the areas on the building that should be insulated. We like to inspect homes that have their heat on in freezing weather - there is a lot one can learn.

This Pennsylvania log home has tight, thick solid log walls and it is not drafty. But the builder didn't bother to insulate under the roof. The huge icicles hanging from the log home's eaves tell the story. If there are high heating bills for this home we'd start by reviewing the ceiling and under-roof insulation of the structure.

While the "R" value of a solid log home is almost certainly less than that of a modern conventionally-framed stud wall home insulated with fiberglass or other products, the wall "R" values alone do not accurately describe the comfort level of a log home.

Provided that the log construction has been well-built without drafts or leaks, the thermal mass of solid log walls is considerable.

But as we discuss at Energy Efficiency of Log Homes, solid log homes are more massive than lightweight wood-frame insulated structures, but a National Bureau of Standards study found that the energy that a log home saves in the swing seasons (spring and fall) through added mass (and comfort for occupants by heating or cooling systems needing to cycle on or off less often) does not amount to much on an annual basis. See THERMAL MASS in BUILDINGS for details about this effect.

Average R-value or Insulating Value of a Solid Log Wall

Solid wood has an R-value of about R-1 per inch of thickness. A round log wall using 8" diameter walls is not, however 8" in uniform thickness; that wall thickness is reached only across the center of each log.

The scalloped wall surfaces will certainly be less than 8" (R-8) in thickness where log faces meet one another. Compute the average wall thickness of solid wood to arrive at a reasonable R-value estimate for a solid log wall. Typically for an 8" log the average log wall thickness is around 6 to 6.5".

Consider Thermal Mass in Addition to R-Value of a Log Home

Log home enthusiasts argue that in measuring comfort one should not only consider the "R" value of the building walls and roof but also the thermal mass of the building. High thermal mass (provided by the mass of solid logs in a log home) means that the building will be slow to change in temperature.

We agree that overcoming drafts and un-wanted air leaks is the first priority for making a building comfortable and for reducing heating or cooling costs in cold climates. INSULATION R-Values & Properties provides detailed estimates of the insulating values and properties of various insulating materials.

A large thermal mass in any building tends to make temperature changes occur more slowly than in structures lacking that feature. As a result, occupants of solid log homes often assert that they find their building very comfortable in both heating and cooling seasons.

Log Slab Sided Log Home Insulation R-Values

Conventionally insulated modern long cabin renovation (C) Daniel Friedman

Slab-log sided homes such as the one shown here and discussed in detail at Slab Log Cabin Siding are generally built over conventional wood-frame walls that allow conventional wall insulation.

This cabin was renovated using 2x6 wall studs to permit extra in-wall insulation as well as the application of solid foam insulation on its exterior walls. The walls of this building were framed to about R-20. Very important as well, the builder did a great job assuring that the home would be draft free.

After a horribly incompetent installation of an in-floor radiant heat system (by the same builder who did so well on framing and insulation) we had to abandon the heating system for this Minnesota cabin. Luckily the cabin is so tight and well insulated that we discovered that we could heat it for at least three seasons using just a few portable electric baseboard heaters. See RADIANT HEAT Floor Mistakes to Avoid.

Frequently Asked Questions (FAQs) about log home insulation and the insulating value of solid logs

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Technical Reviewers & References

Related Topics, found near the top of this page suggest articles closely related to this one.

Thanks to Arlene Puentes for the photograph of a checked log in a log home exterior. Arlene Puentes, a licensed home inspector, educator, and building failures researcher in Kingston, NY. Photographs © Arlene Puentes 2006 All Rights Reserved. Text © Daniel Friedman Arlene Puentes 2008 All Rights Reserved.
"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.

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, 25th Ed., 2012, 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. Field inspection worksheets are included at the back of the volume. Special Offer: For a 10% discount on any number of copies of the Home Reference Book purchased as a single order. Enter INSPECTAHRB in the order payment page "Promo/Redemption" space. InspectAPedia.com editor Daniel Friedman is a contributing author.

Or choose the The Home Reference eBook for PCs, Macs, Kindle, iPad, iPhone, or Android Smart Phones. Special Offer: For a 5% discount on any number of copies of the Home Reference eBook purchased as a single order. Enter INSPECTAEHRB in the order payment page "Promo/Redemption" space.

Building inspection education & report writing systems from Carson, Dunlop & Associates Ltd

Best Practices Guide to Residential Construction, by Steven Bliss. John Wiley & Sons, 2006. ISBN-10: 0471648361, ISBN-13: 978-0471648369, Hardcover: 320 pages, available from Amazon.com and also Wiley.com. See our book review of this publication.
Decks and Porches, the JLC Guide to, Best Practices for Outdoor Spaces, Steve Bliss (Editor), The Journal of Light Construction, Williston VT, 2010 ISBN 10: 1-928580-42-4, ISBN 13: 978-1-928580-42-3, available from Amazon.com
The Journal of Light Construction has generously given reprint permission to InspectAPedia.com for certain articles found at this website. All rights and contents to those materials are ©Journal of Light Construction and may not be reproduced in any form.
Appliances and Home Electronics, - energy savings, U.S. Department of Energy
Avongard foundation crack progress chart for structural crack monitoring
Basement Moisture Control, U.S. Department of Energy
Building Failures, Diagnosis & Avoidance, 2d Ed., W.H. Ransom, E.& F. Spon, New York, 1987 ISBN 0-419-14270-3
Building Pathology, Deterioration, Diagnostics, and Intervention, Samuel Y. Harris, P.E., AIA, Esq., ISBN 0-471-33172-4, John Wiley & Sons, 2001 [General building science-DF] ISBN-10: 0471331724 ISBN-13: 978-0471331728
Building Pathology: Principles and Practice, David Watt, Wiley-Blackwell; 2 edition (March 7, 2008) ISBN-10: 1405161035 ISBN-13: 978-1405161039
The Circular Staircase, Mary Roberts Rinehart
Construction Drawings and Details, Rosemary Kilmer
Crawl Space Moisture Control, U.S. Department of Energy
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.
Domestic Building Surveys, Andrew R. Williams, Kindle book, Amazon.com
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.
Guide to Domestic Building Surveys, Jack Bower, Butterworth Architecture, London, 1988, ISBN 0-408-50000 X
"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
Historic Preservation Technology: A Primer, Robert A. Young, Wiley (March 21, 2008) ISBN-10: 0471788368 ISBN-13: 978-0471788362
Log Homes: Minimizing Air Leakage in Log Homes, U.S. Department of Energy
Manual for the Inspection of Residential Wood Decks and Balconies, by Cheryl Anderson, Frank Woeste (Forest Products Society), & Joseph Loferski, October 2003, ISBN-13: 978-1892529343, $39.00 at Amazon.com or at the InspectAPediaBookstore
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 Design for Engineers and Architects, M. Hatzinikolas, Y. Korany, Canadian Masonry (2005), ISBN-10: 0978006100, ISBN-13: 978-0978006105
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
Masonry, Engineered: Using the Canadian Code, J. I. Gainville, Cantext publications (1983), ASIN: B0007C37PG
Masonry, Non-reinforced masonry design tables, Hans J. Schultz, National Concrete Producers Association and the Canadian Masonry Contractors Association (1976), ASIN: B0007C2LQM
Moisture Control in Buildings, U.S. Department of Energy
Moisture Control in Walls, U.S. Department of Energy
Quality Standards for the Professional Remodeling Industry, National Association of Home Builders Remodelers Council, NAHB Research Foundation, 1987.
Quality Standards for the Professional Remodeler, N.U. Ahmed, # Home Builder Pr (February 1991), ISBN-10: 0867183594, ISBN-13: 978-0867183597
R-Value of Wood, U.S. Department of Energy
Slab on Grade Foundation Moisture and Air Leakage, U.S. Department of Energy
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.
"Vapor Barriers or Vapor Diffusion Retarders", U.S. DOE: how vapor barriers work, types of vapor diffusion barriers, installing vapor barrier
Ventilation for energy efficient buildings, Purpose, Strategies, etc.,
...

Log Home Design, Inspection, Maintenance, Repair References & Product Sources

Log Homes: Minimizing Air Leakage in Log Homes, U.S. Department of Energy
Log Homes: Controlling Moisture in Log Homes, U.S. Department of Energy
Log Homes: Log Home Design, U.S. Department of Energy
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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