Question

What is the value of log construction to meet energy efficiency or other green standards? The logs would be locally sourced.

Asked by Mary Shaw
Ellensburg, WA

We are just beginning to plan for a new home on land we own in Northwestern Montana. Logging and log home building are a big part of the economy in the local community. We are curious whether new materials and construction techniques are likely to outperform logs in creating a healthy, sustainable home.

Answer

Polly Osborne, FAIA, LEED AP

Answered by Polly Osborne, FAIA, LEED AP

Los Angeles, CA

Polly Osborne Architects

July 24, 2011

Log cabins, popular for their rustic aesthetic, are only as energy efficient as the insulation that is installed behind the logs.

  • Wood isn’t a particularly good insulator, having an R-value of 1.28/inch for soft woods and .87/inch for hardwoods compared to standard insulation materials like
  • fiberglass: R-3.33 per inch, and
  • mineral fiber: R-value of 5 per inch.
  • (R-values are the unit to measure the resistance of a material to the transfer of heat or cold.)

Also consider heat loss through structural members like wood or steel

When speaking of energy loss, the R-value of a material is of primary importance, but it isn’t the only thing to think about.

You can have a lovely R-30 wall broken by structural members, like wood or steel, having a low R-value. Then all the heat leaks out of these cracks.

  • Conventional construction heat loss is often through the studs that are in between the insulation.
  • Loss of heat in conventional structures can be mitigated by adding an insulating material in front of the structural wall.

Aesthetic or structural use?

In a log cabin, the big question is: are the logs a cladding for aesthetic reasons? Or are they in the structural layer?

  • If they compose the structure and the cladding, then to have really great insulation, you’ll need another layer behind them to achieve an excellent R-valued wall.
  • If they serve as a cladding only, then you can add insulation behind them, which is to say, between the logs and the structural layer, to achieve a good insulation value.

In addition, I would put insulation between the structural members.  If you would like to know which structural system is the most energy efficient, wood transfers less heat than steel (R-.003/in) or concrete (R-.13/in) but none of them are very good. 

An aesthetic approach

If you like the logs for aesthetic reasons, and they help the local economy, by all means, go for it.

  • Use half-log sections on the outside, add insulation behind them, then structure with insulation, then half logs on the inside if you want the look there.
  • This may seem extreme to some, but you will save a lot of energy this way.


Good luck with your new house!

 

For more information:

Read "I have a log home. Will insulating my interior walls lower my electric bill?" a Q&A answered by Harold Remlinger.

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