Log home insulation retrofit
Hello,
I purchased a log home last year and would like some advice on how to improve the insulation. I know, this question has been asked a few times before but I have a few specific concerns that I couldn’t find exact answers to.
I’m in norther Michigan, climate zone 6. The home is pretty large, 4,000 sq ft two story with cathedral ceilings.. It’s a but-and-pass 6X6 milled square logs with chink on a block foundation with crawl space.The roof is spray foamed with closed cell about 4-5 inches thick and the foundation in the crawl space is also spray foamed. Crawl space has a vapor barrier over the dirt floor but its not sealed to the spray foam (foam done first) and its also not taped at the seams. This winter we were able to keep the main room of the house fairly comfortable using an interior wood stove and about 450 gal of propane in the back up furnace. The bedrooms are another story.
This spring I’m going to have a blower door test done and a general energy audit to help seal any leaks. Im also planning to update the exterior doors and possible the windows. My other main concern are the small 6 inch logs used for construction. I’m going to seal the checks and re-do some chinking. The guy who built this did not seal or use any caulk between the stacks (among other things he did a pretty bad job on that I found after buying). My thought, like others have mentioned, is to build a second stud wall inside to insulate the exterior log walls and cover with either dry wall or tongue and groove knotty pine.
My main question here is if I go ahead and do the second interior wall what issues do I need to worry about in terms of vapor and potential log rot? I have noticed a few areas with water staining on the interior walls, these can be tracked to exterior checks or corner chink that needs addressing. I would like to do a flash and bat with closed cell foam and rock wool over top but the potential for water and log rot has me rethinking. What would be a good option? Rigid foam directly to walls with furring strips for wall finish material v.s stud out and foam/bat or just stud and rock wool? My gut tells me stud and then 2×4 thickness rock wool would be a good compromise of R value and still letting any potential moisture sneaking in/out to not be trapped.
Would adding this extra insulation to just the lower floor bedrooms make much of a difference or is it not worth it unless you do the whole house? The main room and loft get pretty warm from the wood stove but as I stated before, the bedrooms on first floor are the coldest in the house. Also considering radiant floor heat in the bedrooms but that’s another story.
Selling/moving is not really an option but if this house gets to be much more of a head ache than it already is I may be investing in a bulldozer . . .
thank you!
Jon
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Replies
Jon,
I'll give you my opinions, based partly on having one in our family and seeing first-hand how they perform.
Log homes are a terrible way to build. Without constant attention and monitoring, they leak. Thus there is no good way to insulate the interior without the logs eventually succumbing to moisture damage. Exterior insulation is the way to go. I would figure out a way to use mineral wool or cellulose, but some form of foam is probably easier. You can buy log siding to get the look back if you want.
If you insist on insulating the interior, use vapor-permeable insulation (cellulose, mineral wool or fiberglass) and invest in a variable-permeance membrane for the interior, so the wall can dry as easily as possible at all times of the year. Use at least code-minimum insulation; the drying effects of escaping heat won't be enough to dry the logs if you skimp. And keep a very close eye on keeping the logs sealed against water in all its forms.
Air sealing and insulating the entire house will pay off. The upstairs is only that much warmer now because of leaking air and no insulation.
The ceiling insulation sounds scant. This should be at least double the current level for Zone 6. Add to this likely thermal bridging through the framing members and this part of the home also needs an upgrade.