Should a log cabin be treated like reservoir cladding?
I live in a log cabin in climate zone 6 in Maine. Not ideal but working with what I got. The wall assembly from inside out consists of v match pine on a 2×4 interior wall with Kraft faced batts and then the exterior cabin logs. I plan on re-insulating and air sealing those interior 2×4 walls but I was curious if I should pack insulation up tight against the logs like a dense pack cellulose or leave an air gap to promote ventilation and drying of the logs. The logs expand, contract, and take on and release moisture with the seasons so an air gap makes sense to me. I do plan on adding a vapor retarding layer like intello on the interior 2×4 wall/chase.
Thanks.
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DWest,
I'm not sure. The downside of assuming the logs hold sufficient moisture to warrant a gap would be that the gap would allow convective currents reducing the effectiveness of the insulation. Ideally you would run a house-wrap on the exterior side of the stud walls, but if that isn't practical to do I'd use mineral wool batts in the cavities to alleviate that concern.
If you liquid apply air seal with something vapor open the back of the log walls combined with the SVR you shouldn't need a gap between fluffy insulation.
But it does seem like @Malcolm_Taylor 's solution of mineral wool batts and your SVR would be the easiest way to do it.
Do you mean to say that the mineral wool batts are less affected by moisture or convective air flow than other types of of fluffy insulation? The 2x4 interior wall is already spaced about a half inch or more off the logs so initially that's why I thought of dense pack cellulose to fill in the nooks. I was also considering a moody wall type assembly.
My proposed would be: cabin logs, 2x4 wall studs, rock wool batts, smart vapor retarder, 1.5" strapping horizontal, 1.5" comfort-board, and finally dry wall.
DWest,
Yes, mineral wool batts suffer much less from wind-washing. See tables 8 & 9 in this link:
https://www.rdh.com/wp-content/uploads/2017/10/Van-Straaten-Windwashing.pdf
Your proposed wall sounds like a good one to me.
I agree w Malcolm. That wall assembly sounds great.
Good luck
My family has a manufactured log home in western Maine, built in the mid-90s, so I can assure you that yes, logs should be considered a reservoir cladding. Insulating to the interior will keep the logs wetter because they won't be as warm in the winter--indoor heat usually pushes the moisture through the logs. The logs are also the structural system so if they rot it's a much bigger deal than just replacing some siding.
I have thought about it a lot and have landed on the best way to make a log home energy efficient and reasonably safe from mold and rot being to clad the exterior with another material and provide a vented rainscreen behind it. Then it would be safe to insulate the interior. Otherwise, unfortunately, I would not recommend it in our climate.