Log home DER Ideas?
I am a long time reader of GBA and, as a result, would not generally even go near a log house if I was interested in energy efficiency. That said, I find myself considering one due to its location, location, location. Given that, I would like to get some opinions about the best ways to go about retrofitting the house so it is at least reasonably energy efficient. Cost counts, so ‘tear it down’ options aren’t all that helpful to me.
I have only seen pictures of the property to date, discussions here will help me decide if I want to go see it in person. The current house sits on a poured concrete foundation. A full basement sits under a portion of the structure, a crawlspace lies under the remainder. It is a cedar log house with what appears to be ~ 6″ ‘diameter’ logs, the logs are squared off in the interior, creating a relatively flat surface. Large logs (~10-12″ diameter) form the beams and rafters, smaller logs form the purlins, and what appears to be tongue and groove pine runs from the ridge to the eaves. The roof is asphalt shingles. The shape of the logs on the exterior appears to be OK, the shape of all interior members is good to very good.
So, I would love to hear ideas re the best ways to air seal the house and beef up insulation to somewhat reasonable levels. The first things that come to my mind are to chink things as well as possible on the exterior, implement some sort of interior air barrier/moisture retarder and build 2×4 walls inside of the log shell, possibly creating a gap between the framing and the interior surface of the logs and insulate with cellulose or mineral wool. Roof-wise, replace the shingles, taking the opportunity to place foam on top and placing additional insulation between the rafters inside. Thoughts? Other ideas? Warnings?
The house is in climate zone 6, along the coast of Maine.
Thanks all.
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Replies
Hi Rob,
I've thought about this question a lot, as my family owns a manufactured log home in the western Maine mountains. It's virtually impossible to make and keep a log home airtight, and wood is only R-1 to 1.25 per inch, so the insulating value isn't very good either. There is a small benefit from the thermal mass but it doesn't go far.
The logs are thick enough, though, that they can hold a lot of moisture--a serious reservoir cladding--so I would not feel comfortable insulating to the interior, where the logs will stay wet and attractive to decay organisms, ants, and other pests. It's also very difficult or maybe impossible to properly flash around windows, doors and other penetrations. You end up relying on caulking and for the wood itself to be part of the WRB, which doesn't really work because wood is really good at absorbing water.
What the logs do offer is a decent structure (though not ideal) and an interior finish (again, possibly not ideal, but paint fixes a lot of sins and it would be easy to add another interior finish over the logs). What I would like to do at our place, and what I would recommend to you, is to consider the logs the structural layer, and add an air barrier, insulation, and WRB on the outside of the logs. There are many product combinations that could work. In Maine, log homes are not required to conform to the state building and energy code, but of course you should do the best you can, and make sure there is enough insulation to keep the logs above the dew point all year.
Ideally, the insulation layer would be vapor permeable, so on the outside of the logs I would suggest a layer of Pro Clima Intello as a vapor-variable air barrier, then a Larson truss (or I-joists) with mineral wool or dense-packed cellulose to R-30 or better; then a good, vapor-open WRB like Pro Clima Solitex Mento, then furring to create a rain screen. You can clad it with anything; of course cedar shingles are always appropriate on the coast, but log siding would retain the current look to some degree. The windows would probably need to be re-installed, but if they are in good condition and are at least double pane, there is a chance you could work with them in place.
Alternatively, you could use layers of rigid foam on the outside of the logs, with all the pros and cons that go with that approach over any construction system.
For the roof, I would probably just put down nailbase (rigid foam with OSB or plywood pre-adhered to one side). If you are re-roofing anyway, it's the fastest and easiest way to seriously improve insulation levels.
Rob,
Michael gave you good advice. Note that you end up having to build a new building around your log house.
In many cases, doing a good job with this work costs about the same as building a new house.
In an earlier Q&A thread, a reader who owned a log house asked for advice. I remember AJ Builder's answer: "Put the house on the market and sell it."
"Will moving solve your problem?" is always the first question I ask my potential clients. Typically easier and cheaper than major renovations.
But otherwise, agree w/ Mike. And the Larson truss or similar will make it easier to create a reasonably flat plane beyond the logs.
Rob,
I found the old thread. My memory was faulty -- I guess I was the first person to suggest to the owner of a log home that a good solution was to sell the house. (AJ Builder just chimed in at one point to say that he agreed with my advice.)
Here is the link to the Q&A thread: Stopping log home heat loss.
And here is the link to the Q&A Spotlight story that Scott Gibson created from the thread: Fixing a Leaky Log Home.
Rob,
OK, I found a different thread: Log home insulation advice. This must have been the thread I was thinking of.
AJ Builder was the first to respond. He advised, "I build log homes. That said I inform everyone that they are not energy efficient nor an economical choice. ... Best choice is to sell. ...I have built many log homes. I do not own one and at this point never will. They are a luxury home in my opinion though sold as being the opposite at least as to cost to own, build and heat and maintain. Especially those three. Maintenance is the highest of any home I build. Cost to construct is the highest. And cost to heat is by far the highest."
Thanks guys. I failed to do my homework, i.e., go find the answers provided on GBA for the other times this question was asked.
The location of the house was a key motivation in my entertaining what would likely be an expensive, compromise-filled project. Thanks for getting me back on track.