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