Exterior insulation round half-log cabin – advice please
Hi Im looking for advice on how to insulate the exterior of a wooden cabin with half-round logs. The cabin was built from a German kit in the 1980’s, its very dry and solid but no wall insulation.
The logs are solid wood, and interlock with each other. Each log is around 5 inches thick at the widest part and 7 inches tall. The interior side of each log is flat (and will mostly have dry wall attached to it) with the outer face curved outward – roughly an inch of curve across the 7 inch width. Im limited on space internally which is my main reason to insulate externally, plus other advice suggests it’s the better solution.
Im in northern Italy, in Piedmont hills with very hot summers and fairly mild but pretty wet winters (could this be equivalent to a 4A or 5B zone in USA?). I am replacing all the windows to align to the new outer wall.
My starting point is to tie 100ml of rigid insulation panel straight on to the logs (at the outermost part) then batten over the top and then pin siding onto the battens. This leaves an air gap at the top and bottom of each log under the insulation.
I have 2 main questions-
1. is the air-gap a serious enough problem that I should either A) plane the logs flat (a very huge job) or B) find something to fill the gap (if so what would work and flex with the building), or C use a different insulation type which would better mould to the wall shape.
2. where does the vapour barrier go? On the outer-facing side of the insulation and against the siding or on the inner side of the insulation facing against the log. or maybe on the interior under the drywall?
Also just any suggestions on resources to go to for better information – Im not seeing much on line or on you tube about this topic
Many thanks
Paul
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Replies
The hard part with your assembly is defining where the air barrier is. One way might be to wrap the logs in water permeable peel and stick as the main air barrier. You can then strap the logs with the local equivalent of say a 2x4 and insulate with thicker batts. The batts can then be squished to follow the log shape so you don't end up with any voids. From there it is standard assembly on the outside (ie. sheathing/houswrap/rainscreen/siding).
P.S. The nice part of a log home is visible logs. I would not cover both sides, pick one to be exposed and insulate on the other side.
Hi Akos, thanks thicker soft batts to follow the log curves is an idea. Will the insulation still perform where it will be alternating compressed/ un compressed up the wiggly wall?
As to keeping logs on the outside - aesthetically Id agree. However the cabin is only 650 square feet and we need every inch of space for living - so plan is to cover then add wood siding to front elevation only. Alternative is to knock down and start again which is too costly for us and of course not environmentally friendly.
Thanks
Paul
Seems to me your plan destroys the cabin’s charm. Clearly someone spent a lot of money to buy and import and erect a log cabin in the woods. If you cover the logs, it becomes a shed. OK, it is well insulated shed.
Consider enjoying it for what it is install a wood stove and feed it often. It is an experience maybe not one I would want to live 365 day a year but for a week or 3 it sounds great.
If you must have the modern conveniences them build a new one but not to close.
Walta
Walta100 - as a young family, we'd be happy to take a new house and leave the cabin for others to enjoy. However we're also happy to be pragmatic and are lucky to have found something no-one else valued enough to put a bid on. Whilst our money is tight, we are capable and considerate - it will be better left than found.
For insulating your log cabin, use expanding foam to fill the air gaps, it adapts well and saves you from planing the logs. Place the vapor barrier on the interior side, against the drywall, to keep moisture out of the insulation.
Hi Uiloco - thanks, does expanding foam remain pliable to accommodate a bit of wood movement - a particular type to use for this application? and then I suppose I can use solid exterior insulation panels or batts on top of it? So from inside out its drywall, vapour barrier, wood logs, expanding foam in gaps, insulation panels then siding? Thanks
Is the plan to live in the cabin all or most of the year?
Sounds to me like it would be booked continuously as a charming vacation rental with a little clean up.
Walta
it will be our permanent home, we don't have another place to live
Coldtuna,
Forget the log aesthetic, I'd cover the walls with whatever you need to. Exposed they are susceptible to rot and pest infestations, and the upkeep is constant.
How far does the roof overhang the walls?
Will it be enough the keep any new exterior insulation dry?
Walta