R-Value of Log Walls

      Wood rates about R-1 per inch, but air-sealing is also an issue with log buildings. July 13, 2006

What is the R-factor in a red pine log? I operate a sawmill that makes log cabin logs and have been asked this question by building inspectors. I read that you should multiply the width of the log by 1.5 to determine the R-factor. So if you have a 10" log, the R-factor would be 15. Also, does the R-factor increase if the log is kiln dried compared to air dried?

Forum Responses
(Sawing and Drying Forum)
From contributor D:
Wood has an R factor of about 1. It would not make any difference how it is dried. It varies with species, but red pine should be right about there.

From contributor L:
To add to the above reply: dried wood has an average R-value of 1/inch of wood. So your 10 inch timber once dried will have about an R-10 value.

From contributor S:
But log walls have an attribute called thermal mass. Adobe and trombe walls (sp) also have thermal mass, as do large containers of water. Why don't tall water towers freeze solid in the north? They act as a heat/cold reservoir moderating fluctuations in temperature because of stored energy. From what I've read, R values are not really an accurate way to measure thermal masses and are only one factor that needs measured.

From contributor D:
You are right in a way about the mass idea. When the sun hits the outside of a wood wall, it has to heat the wall and thus, there is a time delay from the time the sun hits the wall until the inside sees the effect. But it will see the effect. Since there is a daily fluctuation in sun and temperature, it is not an important issue for a kiln. It is more of an important issue in heating and air conditioning where you have a much different effect from an R8 window than you do from an R8 wall and you consider that when sizing an air conditioning unit. But the net result over the day is not a big enough deal to worry about.
Build a tight kiln and insulate to at least R30. That saves heat but, just as important, prevents condensation from forming, which will destroy the building over time.

From Professor Gene Wengert, forum technical advisor:
Using a multiplier of 1.0 is a conservative approach to determining the R-factor. But the answer is a bit misleading, as there is often a great deal of leakage at the joints. (It is similar to have a well insulated house, but then leaving the windows open.) It is advisable to suggest that the interior walls of a log home also be framed with 2x4s conventionally and insulation added to provide better heat insulation overall. This is especially true for the bathrooms and kitchens. It is important to insulate the floors and ceilings as well, especially in bathrooms and kitchens. Certainly, the drier the log, the better the insulation value (the larger the R-value). This is likely why some people suggest using a 1.5 multiplier, as that would be closer for very dry wood.

Would you like to add information to this article?
Interested in writing or submitting an article?
Have a question about this article?

Have you reviewed the related Knowledge Base areas below?
  • KnowledgeBase: Knowledge Base

  • KnowledgeBase: Primary Processing

  • KnowledgeBase: Primary Processing: Sawmilling

  • KnowledgeBase: Wood Engineering

  • KnowledgeBase: Wood Engineering: Wood Properties

    Would you like to add information to this article? ... Click Here

    If you have a question regarding a Knowledge Base article, your best chance at uncovering an answer is to search the entire Knowledge Base for related articles or to post your question at the appropriate WOODWEB Forum. Before posting your message, be sure to
    review our Forum Guidelines.

    Questions entered in the Knowledge Base Article comment form will not generate responses! A list of WOODWEB Forums can be found at WOODWEB's Site Map.

    When you post your question at the Forum, be sure to include references to the Knowledge Base article that inspired your question. The more information you provide with your question, the better your chances are of receiving responses.

    Return to beginning of article.

    Refer a Friend || Read This Important Information || Site Map || Privacy Policy || Site User Agreement

    Letters, questions or comments? E-Mail us and let us know what you think. Be sure to review our Frequently Asked Questions page.

    Contact us to discuss advertising or to report problems with this site.

    To report a problem, send an e-mail to our Webmaster

    Copyright © 1996-2018 - WOODWEB ® Inc.
    All rights reserved. No part of this publication may be reproduced in any manner without permission of the Editor.
    Review WOODWEB's Copyright Policy.

    The editors, writers, and staff at WOODWEB try to promote safe practices. What is safe for one woodworker under certain conditions may not be safe for others in different circumstances. Readers should undertake the use of materials and methods discussed at WOODWEB after considerate evaluation, and at their own risk.

    WOODWEB, Inc.
    335 Bedell Road
    Montrose, PA 18801

    Contact WOODWEB

  • WOODWEB - the leading resource for professional woodworkers

      Home » Knowledge Base » Knowledge Base Article