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Insulating a log cabin.

Started by Joe Hillmann, January 22, 2023, 12:40:48 PM

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Joe Hillmann

I am in the process of building a log home out of D-logs.

I realize that once it is built at some point in the future cutting firewood will become more difficult as I age and paying for propane or electricity to heat it may become prohibitively expensive.  So I want to have a plan for how I can insulate the walls in the future.  I just dont know if I am overlooking some obvious problem.

My rough plan is to:

cover the outside of the logs with vapor barrier, 

Hang vertical 2x2  from the tails of each rafter on the eaves about 8 inches from the outside of the log wall.  The 2x2s would be conected to the log walls at a couple points with stand offs of some type.

The 2x2s would be covered with tyvek and then some type of exterior siding.

Then the gap between the vapor barrier and tyvek would be filled with dense pack, blown in, insulation.

That way the entire house could be insulated with almost no thermal bonding between the inside and out except around windows and doors.  And it can be done at a fairly low cost.

Am I missing anything obvious on why this is a bad idea?

Will having the vapor barrier touching the logs cause them to rot?  For the time being we will heat the home all winter,  but in the future we may go south for the winter so we are designing the systems in the house to be able to freeze without doing damage.  My concerned is the as the  walls begin to cool the condensation point will eventually move from the exterior surface to the interior surface, that could trap water in places that could lead to rot.

I would also like to include a radient barrier, but I worry that would leave a perfect gap for pests to live in.  As well as add a wonderful cavity to allow fire to spread quickly and unnoticed if we ever had a fire.  As well as add extra complication and cost to the process.

beenthere

Gather that you are planning for the log "look" to be on the inside of the cabin?
south central Wisconsin
It may be that my sole purpose in life is simply to serve as a warning to others

Don P

Thinking out loud. Moisture riding the heat in winter moves through the gaps in the log walls, hits the VB condenses and wets the log wall. That gives me pause, but, it is free to dry in either direction. 

No VB, moisture moves through the gaps, through the insulation, hmm, condensing within it, if the moisture load is high enough. The log wall is a big moisture buffer in either scenario, it can absorb quite a bit and still be below fiber saturation point and rot risk. As long as we are talking normal amounts of household vapor and not liquid water or a cannery going. The warm moist air will find gaps, it whistles through, hits cold, condenses and there is the wet spot. Is it better to use tyvek to block air but allow vapor to pass through?

Joe Hillmann

Quote from: beenthere on January 22, 2023, 01:46:21 PM
Gather that you are planning for the log "look" to be on the inside of the cabin?
Kind of,  I am building with logs because they are free and my area is much more forgiving on log cabin building code than stick built.  If it turns out the inside is too dark or to hard to keep clean we may sheetrock the inside.  The bigger reason to put the insulation outside is space.
The main house is going to be small, only 20x30.  So I dont want to loose any more interior space to future insulation.

Joe Hillmann

Quote from: Don P on January 22, 2023, 01:51:53 PM
Thinking out loud. Moisture riding the heat in winter moves through the gaps in the log walls, hits the VB condenses and wets the log wall. That gives me pause, but, it is free to dry in either direction.

No VB, moisture moves through the gaps, through the insulation, hmm, condensing within it, if the moisture load is high enough. The log wall is a big moisture buffer in either scenario, it can absorb quite a bit and still be below fiber saturation point and rot risk. As long as we are talking normal amounts of household vapor and not liquid water or a cannery going. The warm moist air will find gaps, it whistles through, hits cold, condenses and there is the wet spot. Is it better to use tyvek to block air but allow vapor to pass through?
My thinking (which can be wrong, and why I am asking for input from others) is, as long as the house is heated the logs and vapor barrier will almost always be way above the condensation temp.  And the condensation point will be somewhere between the barrier and tyvek.  So there should rarely be liquid water on the barrier.
I also expect the logs to absorb and release a lot of moisture in the air.

barbender

Stick frame it and put log siding on it. I've seen a local guy use slabwood to side houses, he scribe fits it and it looks great.
Too many irons in the fire

Joe Hillmann

I cant afford to stick frame it.

Ianab

Quote from: Joe Hillmann on January 22, 2023, 12:40:48 PMWill having the vapor barrier touching the logs cause them to rot?  For the time being we will heat the home all winter,


My concern with that plan would be that the logs won't be dry when you build, because it takes a few years for big pieces of wood like that to dry out. If both sides of the log are exposed, it's OK, they gradually dry out, the whole structure settles a bit, and all is well. 

But if you put a vapour barrier / insulation over the walls you are probably going to get condensation  from the moisture leaving the logs being trapped in the internal spaces. I can't see that being a good thing. 

Also there is the issue of the logs shrinking as they dry, and what that will do with the exterior cladding. The logs walls will probably settle several inches. You have to account for that with your door and window gaps, but how are the 2x2 battens and cladding going to react? 

Now if you build it un-insulated, and let it all dry out, THEN clad and seal things up. That might be OK?
Weekend warrior, Peterson JP test pilot, Dolmar 7900 and Stihl MS310 saws and  the usual collection of power tools :)

Joe Hillmann

The logs are on there second full year of drying in the pile, and insulating would not be done for another 10+ years, if at all.

The logs should be more or less dry, but season moisture changes may still cause the height of the walls to grow and shrink.

I need to measure how much it changes per year and have a plan for that, which I had considered for inside, bit not for outside.

barbender

 A log wall will always settle once assembled, it doesn't matter how long the logs season beforehand.

 Seriously, I would try to find a way to just stick frame it if you are going to do all of this work down the line. It is a lot of extra work for not a lot of savings right now.

 That said, there are lots of people that go to renovate an old house and are surprised to find beautiful logwork behind the siding, and sheetrock or plaster on the inside. I'm sure you can make your idea work, the important thing is to let those logs reach equilibrium moisture content before you seal them in the wall. 

 I don't like the idea of the vapor barrier on the outside of the logs. Maybe it wouldn't be a problem, but I'd way rather have it on the interior side where it will keep interior moisture from passing through.
Too many irons in the fire

Ianab

Quote from: Joe Hillmann on January 22, 2023, 05:24:57 PMinsulating would not be done for another 10+ years, if at all.


OK, After 10 years the logs should be well dry and settled. In that scenario I don't see a big problem. The logs won't be releasing extra moisture, and dry wood can actually absorb a lot of moisture from the air if the humidity around it get's high. Even if you released steam into that gap, the logs would soon soak it up, and maybe only gain 0.5% in moisture, and then gradually release it again over time. You wouldn't want that continuously of course, but that's not going to happen. 

I still don't know if it's the "best" building plan, but if the logs are dry I'm less concerned. Large amounts of water shouldn't be getting into the wall structure, so I don't see the risk being any higher than any other sort of wall construction. 
Weekend warrior, Peterson JP test pilot, Dolmar 7900 and Stihl MS310 saws and  the usual collection of power tools :)

firefighter ontheside

How thick are your D logs?  My logs are red pine and average about 14" thick, but they are scribed, so at the scribe they are only about 6" thick.  Our house has always seemed to right on par with energy costs of regular framed and insulated homes.
Woodmizer LT15
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barbender

If you get your logs sealed up well, most of the heat loss is through the roof. I'd build that in a way that is well insulated in the first place.
Too many irons in the fire

Joe Hillmann

Quote from: firefighter ontheside on January 22, 2023, 09:22:39 PM
How thick are your D logs?  My logs are red pine and average about 14" thick, but they are scribed, so at the scribe they are only about 6" thick.  Our house has always seemed to right on par with energy costs of regular framed and insulated homes.
When milling them I was trying to get them 7 inches or more at the narrowest point (the top and bottom of the D)
From my time in other log cabins I expect it to be reasonably easy to heat with no insulation.  But I want a plan for the future if I find out otherwise. Or if heating costs skyrocket.

Joe Hillmann

Quote from: barbender on January 22, 2023, 09:33:02 PM
If you get your logs sealed up well, most of the heat loss is through the roof. I'd build that in a way that is well insulated in the first place.
The roof will be insulated with 12 inches of foam with a total thermal break between the inside and outside.    So the roof will be pretty well insulated. I also figure in the future once the kids move out I could lay insulation on the upstairs floor to help keep the heat on the main floor.

cabindoc

Joe, I have been building and restoring log homes for 20 plus years.  You are building a uniformly milled "D" log home that is very common.  I replace rotted logs 20 houses per year.  I also live in a log home.  8"D uniformly milled pine.  So, I know what I'm talking about.  The logs are the best insulation known to man.  The logs will have an equivalent R rating as around R22 if you factor thermal mass.  There are calculators on line if you need to know the exact #.  Here is my advice;  As stated, insulate the hell out of the ceiling/roof area...R38 or better, place a thermal break in the ground.  IOW, if you are building on a crawl or post off the ground, you will want 6 mill plastic and a layer of stone or better yet concrete to prevent moisture from coming up from below.  Insulate the hell out of the floor, R21 depending on the floor joists.  And lastly, caulk ALL horizontal and verticle joints and all doors and windows around the house with a textured caulk made by log home specific companies.  IE log jam, weatherall, permachink etc...  IOW, you are trying to create a tight building envelope that you would normally get from conventional construction using sheetrock.  Honestly, the caulking of the joints and seams is the most important as otherwise, you lose heat through all those micro gaps that you're not aware of.  Another tip, use Butyl between the logs to help with the sealing process and lag logs down with 1/2"x12" lags.  IF, in 10 years you want to cover the outside, I would attach 15# felt first, then attach lath strip every 16", sheath with 7/16 cdx and 15# felt again and depending on siding choice you can side or illuminate the felt and sheathing as in log siding that's 1 3/4" thick. Just putting the felt on the logs will act like you put a blanket around the house.  Your heat battle is won or lost in the ceiling/roof.   The caulk will prevent moisture from coming from the inside of the house and if done properly, as long as the log walls dont get wet, ambient air moisture is not enough.  It will go up and down and the log walls will be fine.  This all assumes they are DRY and not wet.
Scott  aka cabindoc  aka logologist at large
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Joe Hillmann

Cabindoc.

Thanks for the pointers.

Do you have an opinion on using cement for the chinking between the logs?  I am going to have a 1 inch gap between my logs.

My plan is to chink it with wire mesh and cement on outside of the cabin then from the inside pack some type of insulation into the gap then chink the inside with wire mesh and cement.  I don't know what the insulation will be yet it could be fiberglass, cellulose, or some type of spray foam.

Don P

Portland cement in contact with wood is the kiss of death, it traps moisture. IF you can keep rain off the walls a lime based chink would be traditional. Modern chinking products stretch and stick.

Joe Hillmann

The walls should never get wet.  There will be a 10 foot wrap around porch on all 4 sides of the house. 

If it turns out the house is too small some of the porches may get walled in and become living space, that would make the log walls interior walls then.

Otis1

As stated earlier, chink that is meant for log homes sticks to the logs and expands/contracts and mostly remains soft so it keeps a seal throughout the seasons. Concrete dries hard and is brittle, so any movement of the logs means cracks and pieces breaking out. I think you would be disappointed with the results after a few years. Most log homes use foam backer rod (different diameters for the application) and chink.

I would think with D logs that the bigger concern is making sure you're sealed between logs. I think this was mentioned above with caulk. 

If you are just building a cabin now and then turning it into a house later, I would build it as tight as you can. Then give it some coats of stain a couple years in a row. When the stain is good and dry then do the chink. It is a pain in the ass to stain a chinked log home (after its chinked), but they are beautiful. By giving it the coats before chink you are protecting all of the wood and hopefully postponing any need for staining for awhile. 

I'd probably leave the log look on the outside and insulate the inside with some 2" foam. Also give a space to run some electrical. Drywall interior is easier to clean.

Don P

When I read there is a gap between the logs... the solid timber wall potentially just became a series of spanning beams supporting a roof. Check your spans or block the gaps in vertical columns pretty frequently.

We have morphed terms from the way I've heard old timers use them. In a traditional log home the "chink" in the gap was split saplings, hewing chips, flat stomes, corn cobs, etc... a load bearing something in the gap. This was "daubed" with clay, then burnt slaked lime, "slack lime", and river sand. There are many variations on the "recipe" going back to pre roman times.



 


 



 

I don't know if your news feeds have been blowing up the past week or two. Apparently we have "discovered" why roman concrete survivse so much better than modern stuff. They were slaking their lime for concrete the same way the masons were. They mixed quicklime, sand and water and slaked it for all of about 30 minutes and used it "hot mix". This leaves telltale unslaked but burnt clasts of quicklime in the product. That is one way I can spot how the old masons were working on a job. That's hot mix and chestnut chips in the top pic, clay and structural cobs in the lower. Shimmed furring strips for high class upgrade in the middle.

Apparently some grad student has rediscovered what every old time mason knows. If there is free lime in the joint, it can flow to and heal minor cracks. From where I'm sitting its a good thing, they snatched lost knowledge back from the gap of my generation.

I need more coffee. Where were we  :D

Oh, insulating outside puts the thermal flywheel inside the envelope, insulating inside puts the flywheel outside the envelope... kiss it or curse it  ;).

Stephen1

I built the log cabin you see by my name. I thought it would be cheaper than stick built. Guess what, build it properly and as much to code as possible and it will cost as much if not more. Your labour will be more also for the life of that log structure. 
Cabindoc has it down pat. Use proper chinking, it works, I put permachink on 15 years (it still there) as I built the cabin, seal the joints with butyl  strips, stain as soon as possible. There is no problem staining the new types of chinking. Do not wait a few years as the stain will not stay on and it will be way more work. 1 coat of stain should go on the logs even before you build. Maintenance is way cheaper than refurbishment. You will need to stain every 3-5 years depending on the sun. Logs get way more sun damage than regular siding, as the upper curve sees more sun, and lower curve gets the reflection from the winter sun. 
The reason people side log homes inside and out is the amount of work it takes for upkeep. They are a living breathing structure..... disturb that and you have rot and more refurbishment.
IDRY Vacum Kiln, LT40HDWide, BMS250 sharpener/setter 742b Bobcat, TCM forklift, Sthil 026,038, 461. 1952 TEA Fergusan Tractor

Joe Hillmann

Don P

The original plan was to stack the logs directly on each other.  When first sawn the top and bottom of each log was parallel.  But since each log is more or less boxed heartwood with the heart way off center, after 2 years of drying they are no longer parallel.

My options are to re saw each log and loose height or shim between each log and have a gap.  Since I like the look of wide chinking I decided to go with 1 inch thick shims.  That way I get the look I prefer, and gain an extra 16 inches of height.  The shim will be spaced every two feet and kept in as vertical of a line as possible between the logs.  Each shim will have to be custom fit with a mason line and a level.  But that should keep the walls straight up and down and keep the logs nice and straight end to end as well.


Joe Hillmann

Several people have commented on how expensive a log cabin is to build.

I think I can build it for around $10,000.

The biggest expenses will be the roof insulation, tin roof, fastners, and batteries.

beenthere

Quoteshim between each log and have a gap.  Since I like the look of wide chinking I decided to go with 1 inch thick shims.  That way I get the look I prefer, and gain an extra 16 inches of height.  The shim will be spaced every two feet and kept in as vertical of a line as possible between the logs.  Each shim will have to be custom fit with a mason line and a level.  But that should keep the walls straight up and down and keep the logs nice and straight end to end as well.

Sounds to me like you maybe talking about a spline. Sliding in a wood piece in straight dado slots between logs.
south central Wisconsin
It may be that my sole purpose in life is simply to serve as a warning to others

Hilltop366

I wonder if a two piece tapered shim would work, once the log was in place put one row in from one side and tack in place then go to the other side and put the top in until snug. It would save you from custom fitting every shim. If the shim was designed with very little taper it should stay in well, the bottom shim would be thick with only ¼" taper taking up most of the room and the top shim would thin. Once the walls have dried a while the shims could be snugged up again before inside chinking.

Joe Hillmann

I dont think that would work.  Because the top and bottom of the logs are no longer parallel the gaps between the logs also wont be.  Whereas a stacked set of shims will have a speceffic angle between top and bottom that wont change no matter how you slide them together.

Hilltop366

That could cause issues, I'm thinking it will be a long tedious job making individual sized shims for an entire cabin. (if I was reading one of your previous post correctly) My brain seems to go to "how can I make this easier" mode automatically. :D

Another idea I had was to make a guide jig to run a drill bit a little bit bigger than the gap between the logs so that you are cutting a little bit of wood off of both logs then use a dowel the same size as the drill bit for your shim. Thinking this would be done on the outside and stop before reaching the inside and cutting the shim short enough to cover it with chinking when done. One question I can see is will a 1¼" or 1½" dowel have enough bearing surface to do the job, they could be put closer together to reduce the load on each dowel.


Stephen1

Drill a 3-4 1/2" holes into all the logs using a jig so all the holes are in the same spot for each wall. Then drop them down over 1/2" threaded rod, maybe even a washer and nut every row or 2, tighten it all down and chink with permanent chink.  On second though just a big nut on top and bottom so you can tighten for a few years as the log wall is still going to shrink for a few years .
IDRY Vacum Kiln, LT40HDWide, BMS250 sharpener/setter 742b Bobcat, TCM forklift, Sthil 026,038, 461. 1952 TEA Fergusan Tractor

Joe Hillmann

I think the drill bit idea would probably work.  

My plan is to strech a line the length of the log where I want the front top of the shim to be.  Then use a level to mark the slope of the log.  From there I can cut the shim on a small bandsaw.

I planned to use a mason line but after thinking about it a dacron fishing line may work better.  I can strech it tighter, it will catch less wind and by being thinner it should be more accurate.

I dont think I need super accuracy.  Because with this method inaccuracies dont add up between layers.

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