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Allthread in log walls/securing roof.

Started by Coastallogger, October 07, 2021, 02:18:53 PM

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Coastallogger

Hi Folks,

I am about to start a log cabin in the Appalachian style: 2 sided logs, half dovetail corner notches...

I suppose this question applies to all log cabin styles though.

But for extra context, this is the style:

http://www.squarepegtimberjoinery.com/home.html

https://m.youtube.com/watch?v=VS9xNxg_nRI

The style has some pretty well-established best practices, but not everyone agrees with The Bearded Carpenter's (see YouTube channel above) use of all-thread ran through all the logs near the corners to cinch all the logs together.

Does anybody know the pros and cons of it? 

My thought is, I am securing the rafters to the top plate log, but without allthread running to the bottom log, you essentially have only the top course of logs holding on the roof.

In my case, with a 20x20 building, this works out to potentially just over 1,000 lbs holding the roof down, not including the weight of the roof itself, which,  with a 3' overhang on the gable ends, seems like not a lot for the potential lift it could experience.

Now I am not an engineer, but my intuition sees this roof flying away with the top course of logs one day without allthread holding all the courses together. But given so many people are building without it, maybe this is way off?

Building 20X20 dovetail log cabin off grid.

Joe Hillmann

There are ways other than allthread. 

Long screws to screw each layer to the one below.
Big nails to nail each layer to the one below.
Nails made from rebar to nail each layer to the 3 or 4 layers below.
Wooden nails used the same as the big nails or rebar.

You could put some kind of strapping on the inside or outside of the wall.

On mine I am thinking of running used elevator cable inside the walls from the foundation, up over a rafter with a steel plate on top of it and then back down inside the wall back to the foundation with some method to pull the cable tight as the logs shrink.

I have seen 120 year old buildings where the rafters were pegged into the top beam and the gables were boarded up to also tie into the top plate.  They survived every storm of the last century. 

But I also helped clean up a house after a tornado where the garage roof completely separated from the rest of the garage between the double top plates, most hangers went with the roof but a few stayed with the walls.

Coastallogger

Quote from: Joe Hillmann on October 07, 2021, 02:38:13 PM
There are ways other than allthread.  

Long screws to screw each layer to the one below.
Big nails to nail each layer to the one below.
Nails made from rebar to nail each layer to the 3 or 4 layers below.
Wooden nails used the same as the big nails or rebar.

You could put some kind of strapping on the inside or outside of the wall.

On mine I am thinking of running used elevator cable inside the walls from the foundation, up over a rafter with a steel plate on top of it and then back down inside the wall back to the foundation with some method to pull the cable tight as the logs shrink.

I have seen 120 year old buildings where the rafters were pegged into the top beam and the gables were boarded up to also tie into the top plate.  They survived every storm of the last century.  

But I also helped clean up a house after a tornado where the garage roof completely separated from the rest of the garage between the double top plates, most hangers went with the roof but a few stayed with the walls.
One thing I hear about pegs and spikes is that if they aren't perfectly vertical, they will hang up while settling, being you crooked chinking gaps. Screws would give better hold, but definitely hang up while settling. 
Of course spikes would give some bite, but nails generally don't have much pull strength, they are used in sheer applications. I understand the sheer strength is their main purpose: to keep the walls flat instead of having one course bow out from the rest as it dries.
But of course if there are old cabins still standing, maybe I am over-engineering.
Building 20X20 dovetail log cabin off grid.

Joe Hillmann

One good thing about wooden pins is you don't have to plan for windows.  One cabin I looked at the guy only used screws in the corners then full length logs for everything. His plan was he could figure out the floor plan and window and door placement once it was built.  And since he used wooden pegs he could cut in a window or door anywhere he wanted without concern of hitting a bunch of randomly placed spikes or screws.

Coastallogger

Quote from: Joe Hillmann on October 07, 2021, 03:10:42 PM
One good thing about wooden pins is you don't have to plan for windows.  One cabin I looked at the guy only used screws in the corners then full length logs for everything. His plan was he could figure out the floor plan and window and door placement once it was built.  And since he used wooden pegs he could cut in a window or door anywhere he wanted without concern of hitting a bunch of randomly placed spikes or screws.
True. I am not the type to be randomly placing anything in any case though. And my design is passive solar so the windows are a key part of the design.
I like the wooden peg idea though for future changes. Once I have forgotten where I put them and want to put in a new window!
Also, I am strategically placing windows and doors to avoid too many full length logs to make my logging and log handling easier because I am not using heavy machinery in the build. The fewer full-length logs I have, the easier my work will be.
I made reply to one of your other posts you must not have read yet though. Would be stoked to have your take on that one too. I liked reading about your build.
Building 20X20 dovetail log cabin off grid.

Don P

Quantify load and provide resistance. You should be able to trace an adequate and continuous load path from ground to ridge in all directions of force, down, up and sideways.

Allthread is fine I've done it several times. you can couple directly to the foundation anchor bolts. We hit corners and beside openings. Depending on the access you leave they can provide down pressure to keep lateral joints snug as they season. You noted that your actual corner load is around 1,000 lbs, that isn't much helping keep logs straight and tight as they season.

 Lag screws are fine, the prebores are vertical and oversized in the upper log so the screw is countersunk in and not attached to the upper log, it can slide down but resist uplift and lateral. Modern log screws are reduced shank that is slick coated, threaded on the end only, they are designed to allow the upper log to slide down. I have seen unrestrained plate logs slide, overturn, snap 1-1/4" corner pegs the builder intended as rafter thrust restraints.

Pegs, rebar, "dowel type fasteners" generally have lower uplift, withdrawal, numbers than something threaded.  


Coastallogger

Quote from: Don P on October 07, 2021, 06:02:04 PM
Quantify load and provide resistance. You should be able to trace an adequate and continuous load path from ground to ridge in all directions of force, down, up and sideways.

Allthread is fine I've done it several times. you can couple directly to the foundation anchor bolts. We hit corners and beside openings. Depending on the access you leave they can provide down pressure to keep lateral joints snug as they season. You noted that your actual corner load is around 1,000 lbs, that isn't much helping keep logs straight and tight as they season.

Lag screws are fine, the prebores are vertical and oversized in the upper log so the screw is countersunk in and not attached to the upper log, it can slide down but resist uplift and lateral. Modern log screws are reduced shank that is slick coated, threaded on the end only, they are designed to allow the upper log to slide down. I have seen unrestrained plate logs slide, overturn, snap 1-1/4" corner pegs the builder intended as rafter thrust restraints.

Pegs, rebar, "dowel type fasteners" generally have lower uplift, withdrawal, numbers than something threaded.  
Lag screws! Good point that they are only threaded on the end. I have heard about wooden pegs snapping as well.
 
Would probably go with the thick kind, not those thin modern structural screws. 
Did you mean "log" screws? Is there one built just for that purpose? Or did you mean lag?

I am not that concerned with continuing the load to the ground. It's a gmcold climate subject to frost heaving. If the logs are not free to move on the piers, there will be some incredible stresses on the piers and bottom course which could skew the whole thing.

My thinking is if my neighbor's 20 foot travel trailer weighing just over the weight of a single course of logs doesn't blow away, my 20 foot cabin shouldn't either. Down to the bottom course I am happy with. Especially if there are old cabins still around with the roof and logs only pegged.
Building 20X20 dovetail log cabin off grid.

btulloh


What have you got against the structural screws?  They're much better than lags in all regards. Widely used in logs and timber. Just curious why you dismissed them so quickly. 


( I'm Pretty sure Don P meant lag when he wrote lag, but he'll be back at some point to speak for himself.)
HM126

Coastallogger

Quote from: btulloh on October 07, 2021, 06:39:07 PM

What have you got against the structural screws?  They're much better than lags in all regards. Widely used in logs and timber. Just curious why you dismissed them so quickly.


( I'm Pretty sure Don P meant lag when he wrote lag, but he'll be back at some point to speak for himself.)
So we are on the same page, I am thinking of these structural screws. (But longer of course)
https://www.homedepot.com/p/GRK-Fasteners-5-16-in-x-4-in-Star-Drive-Washer-Head-RSS-Structural-Screws-100-Pack-772691122254/301878339
My thought with those is the us are so skinny, that the wood would just give around them, even if the screw doesn't fail.
That is why I would think these would hold better as long as the screw itself doesn't fail, which I would doubt it would.

https://www.homedepot.com/p/Everbilt-5-16-in-x-2-in-External-Hex-Hex-Head-Lag-Screws-25-Pack-88700/203151842
Building 20X20 dovetail log cabin off grid.

btulloh

Different page. Check out TimberLok. A completely different animal. There are other brand names but Timberlok is representative of the class. Variety of heads, stronger than standard lags, less labor to install.
HM126

Don P

I just wrote a diatribe on lags and log home screws in the last day or few.
Here it is;
16x24 Guest cabin build with black locust and maybe walnut? in Timber Framing/Log construction (forestryforum.com)

There is what I meant about a continuous load path in all directions. You have a loaded rigid box up on piers, now apply lateral load. Building codes put piers in the engineer required category for foundations because of the number of failures.

Coastallogger

Quote from: Don P on October 07, 2021, 09:14:37 PM
I just wrote a diatribe on lags and log home screws in the last day or few.
Here it is;
16x24 Guest cabin build with black locust and maybe walnut? in Timber Framing/Log construction (forestryforum.com)

There is what I meant about a continuous load path in all directions. You have a loaded rigid box up on piers, now apply lateral load. Building codes put piers in the engineer required category for foundations because of the number of failures.
Thanks. I bookmarked that one for reference later.
I guess the good thing about the skinny ones is no pre-drilling required. Save a ton of time. Way cheaper too. The thick ones would run up really quickly.
I was surprised to learn there IS such a thing as a log screw. But it works through pull-down pressure to straighten out warped and twisted logs.
But my thought with that is if you are building with green wood like I am, when it dries and settles, that pull-down pressure will disappear.
If it weren't for that, I would ditch the allthread holes on the corner entirely. It would save some time preparing the logs. But you can tighten the allthread as it settles, which you can't do for log/lag screws. 
As for piers, I came to the same conclusion. Concrete piers, are far too finicky for a DIYer IMO. And if you get it wrong, that's a huge problem to fix.
Instead I am going to lay down some crushed stone, cut out some railroad tie size heartwood, give it a heavy treatment of Shou Sugi Ban, borate, and  linseed oil or similar treatment, and stack them a few layers in alternate directions with the grain horizontal, spiking together. Then I will lay those on the gravel pad with a capillary break between them and the bottom course of logs. They will remain unfastened to the floating "piers". That way if frost heaves form under them, they will not cause much stress on the structure. It will also make shimming a cinch to keep it level over time.
Building 20X20 dovetail log cabin off grid.

Don P

It's been awhile since I checked priced but lags to structural screws was not a big material cost advantage, it was labor. When we did that for a living the structural screws were coming in towards the end. I would stock a few boxes of lags when we started those jobs. The withdrawal strength of a lag, its ability to pull ornery logs and timbers around, was higher than structural screws. If the log screws wouldn't pill things tight we would break out the lags.

On hanging up, divergent fastener angles, a trim nail, caulk on the vertical trim is an adhesive. Twist, binding log to fastener. Friction. Just remember shrinkage and settlement are 2 different things, hopefully related, but alas, not necessarily :D.

What are the issues with getting to frost depth and coming out of the dirt with masonry? Untreated foundation with a little flamethrower treatment and some fungi food applied is no match for soil borne rotters. You'll be revisiting that within a decade, probably with internal galleries up into the main structure.

I can't remember which of you was mentioning using bubble wrap. I had a client fall for that once, unfortunately on a million dollar home. If you feel warming going on it is because that thing is bleeding btu's. Only after the fact did I learn of the Federal Trade Commission's issues with their claims. Bubble wrap, foil or not, is a packaging material. It is a poor insulator and reflective barriers do have caveats with them.

Do remember when looking at alternatives that builders run in a competitive environment. If it is cheaper, easier, or works better for the buck you will see them adopting.  

Wow, that was a downer, well, better I guess to have the good and bad in mind. Gotta go unload a fridge so we can move it and drop a floor out from under it, the bugs had a party.

firefighter ontheside

If your logs are not dry, you will have to account for all thread to be tightened occasionally and possibly have extra cut off.  My house has 3/4" all thread all the way thru the 10' log walls and extending into the basement.  There are big springs in the basement.  I had to tighten every 6 months or so for the first several years and then cut off the extra before it hit my foundation wall.  My home is coped and scribed red pine that was green when built.  Total shrinkage was about 5" over a 10' wall.  The all thread was placed thru a plastic pipe sleeve that was put in as we stacked the logs.  It was short enough that it was not too long after shrinkage.
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Coastallogger

Quote from: firefighter ontheside on October 08, 2021, 09:24:21 AM
If your logs are not dry, you will have to account for all thread to be tightened occasionally and possibly have extra cut off.  My house has 3/4" all thread all the way thru the 10' log walls and extending into the basement.  There are big springs in the basement.  I had to tighten every 6 months or so for the first several years and then cut off the extra before it hit my foundation wall.  My home is coped and scribed red pine that was green when built.  Total shrinkage was about 5" over a 10' wall.  The all thread was placed thru a plastic pipe sleeve that was put in as we stacked the logs.  It was short enough that it was not too long after shrinkage.
Thanks. I have heard about the springs. Seems it would really reduce the amount of times you need to tighten. Where did you find the springs? That's a pretty specific product.
Building 20X20 dovetail log cabin off grid.

firefighter ontheside

My log shell was built in MN and then dismantled and shipped to MO.  The log builder supplied the springs and I don't know where he got them.  I think he is out of business now.   Yes, the springs help to keep pressure on the logs as they shrink.
Woodmizer LT15
Kubota Grand L4200
Stihl 025, MS261 and MS362
2017 F350 Diesel 4WD
Kawasaki Mule 4010
1998 Dodge 3500 Flatbed

Coastallogger

Quote from: Don P on October 08, 2021, 08:23:22 AM
It's been awhile since I checked priced but lags to structural screws was not a big material cost advantage, it was labor. When we did that for a living the structural screws were coming in towards the end. I would stock a few boxes of lags when we started those jobs. The withdrawal strength of a lag, its ability to pull ornery logs and timbers around, was higher than structural screws. If the log screws wouldn't pill things tight we would break out the lags.

On hanging up, divergent fastener angles, a trim nail, caulk on the vertical trim is an adhesive. Twist, binding log to fastener. Friction. Just remember shrinkage and settlement are 2 different things, hopefully related, but alas, not necessarily :D.

What are the issues with getting to frost depth and coming out of the dirt with masonry? Untreated foundation with a little flamethrower treatment and some fungi food applied is no match for soil borne rotters. You'll be revisiting that within a decade, probably with internal galleries up into the main structure.

I can't remember which of you was mentioning using bubble wrap. I had a client fall for that once, unfortunately on a million dollar home. If you feel warming going on it is because that thing is bleeding btu's. Only after the fact did I learn of the Federal Trade Commission's issues with their claims. Bubble wrap, foil or not, is a packaging material. It is a poor insulator and reflective barriers do have caveats with them.

Do remember when looking at alternatives that builders run in a competitive environment. If it is cheaper, easier, or works better for the buck you will see them adopting.  

Wow, that was a downer, well, better I guess to have the good and bad in mind. Gotta go unload a fridge so we can move it and drop a floor out from under it, the bugs had a party.
I made a reply to this earlier but it didn't show up here so forgive me if I am missing it and repeating myself.
Do I understand you right that the screws will lose their tension with shrinkage/settlement? In that case they won't make a replacement for allthread at the corners for transferring tension all the way to the bottom logs.
I think you have me sold on structural screw for keeping the courses in line, and the larger lag screws if those strip on a particularly twisted log as those have more biting power I hear.
The issues with going below frost line with masonry is the frost line is pretty deep where I am 6.5 feet or so. Which makes for a huge volume of masonry. Since I know little about masonry, and I am roughing it until I can move into my build, the extra time and money will be a buzzkill. Plus if I get something wrong, it's a much bigger headache to fix than floating "piers" where if I get ten years out of em before replacing, I will still probably have saved time and money by the time I die compared to masonry, even if I got it right. I am concerned about creating a "ladder" to the sill logs for soil-borne decomposers, but thought a capillary break on the top would be an effective barrier against that. I am reading borate works against fungi as well, but really mixed reviews on Shou Sugi Ban. But really it doesn't have to last forever since it will be so easy to jack a corner and slip a new one in. Would take a guy an afternoon.
It is me considering the bubble wrap. I am interested to hear what issues your client had with it and how it was put on. My plan was to put it in a continuous sheet between the log joists and subfloor, or between the subfloor and finish flooring. That would give a vapor barrier and provide protection against radiant heat escape. Then if that proves to be not enough insulation, the joists would be spaced 22 1/2 apart, so I can crawl under and put in rock wool sized for 24 OC joists, then cover it up with plywood and/or hardware cloth.
Then if the bubble wrap turned out to not be great at keeping me warm, at least it still serves as a vapor barrier and thermal break to help with thermal bridging of the joists.
The issues I hear of people who use fiberglass and similar under their log cabins is that critters and bugs love to nest in it. And it can be difficult to seal your insulation cavities perfectly since logs are constantly changing shape and size.
I hear what you are saying on best practices being best practices for a reason, but conventional best practices are formed in conventional builds, which is not at what I am doing. Also, being in the forest, there are more critters and bugs to contend with compared to a more sterile suburban site. A lot of log cabin owners complain that bugs and critters love fluffy insulation and steal it to make nests, or just take up residence there and eat away at your floor joists. The bubble wrap apparently critters want nothing to do with, which is a plus.
I understand as well that industry code and energy efficiency standards largely ignores the effect of radiant heat. It focuses more on the air temperature itself, but ignores that you can be much more comfortable in a cooler air temperature if you have radiant heat is being reflected at your body. This is why incandescent bulbs can actually save energy in a cool climate even though they burn more energy per lumen than LED. They slightly warm your body when you are near them with radiant heat, allowing you to be more comfy in cooler air. But they got banned. But I digress.
But certainly combining the radiant properties of the bubble wrap and making use of it as a vapor barrier/thermal bridge, plus using stuff with r-value like rockwool might be good.
All depending on your client's particular issues with the stuff which I am keen to hear.
Building 20X20 dovetail log cabin off grid.

Don P

I think the company that sold it was claiming R-10 under a radiant slab, concrete directly poured on it. I think it was fancier double bubble, an awesome packaging product. That was about 15 years ago in the radiant heyday and before the FTC interceded. We had radiant foil around the sauna and a few other bleeding edge frills. The next one I did in that neighborhood had R-20 of foam under it. 

I was trying to think of what the edge insulation was on those slabs. They both had insulated precast concrete foundations on a gravel trench. The slab edge butted their foam edge. The Superior Walls installation manual used to be on their website. It has good gravel trench info. That is a good basement system if available. Call the excavator, prep the dig and gravel trenches, the truckloads of precast arrive and they set the foundation in a day.

Replacing the ridge cap is easy, the foundation, less so. It's easier to lay block or fill forms when you aren't bumping your head on the house above you.

Any log to log connection is going to loose its compression on the joint as the logs shrink. That is what the counterbore is for with a lag. If the log shrinks and slides down the lag, if the head of the lag was flush with the top of the log, it is going to hold up the next log above it. The driver for settlement is gravity. The threaded rod goes through the stack so there is potential to snug down on the stack. You can help gravity.

It is impossible to pull down an entire stack tight with the rods. That is what the lags or structural screws do, pull things down tight as you stack. Then the threaded rod can maintain at least that and has potential to snug things down more as it shrinks. Springs are available from log home supply houses, Schroeder's is one. Notice the spring compression strength vs the tensile strength of the rod. If you tighten religiously early and taper off as it dries you can apply more force with the nut and a large washer than the spring can. Don't be holy roller religious, you can break the rod, that is where the spring has an advantage.

If it is just a few very widely spaced rods and depending on the beam strength of the log you can very well pull those places down but not the whole. If the rods do not connect to the foundation anchor bolts do provide an alternate connection from logs to foundation, there's many ways to skin that cat.

Stephen1

I keep waiting for my roof to blow off. We have had some great windstorms, but not the once in a hundred years. the roof is still here. I have waken up in the middle of the night hearing a great roar from the wind. It did not take me away.  8) 
I had to have a permit to build my cabin.  Everyone was worried about the bottom course of logs being pinned to the ICF fondation wall. I have the bottom course secured, 1/2" treaded rod, just like they asked, and the SIP roof panels are screwed to the top log on the wall and ridge pole with 12" timber lock screws, just like the engineers asked.  Not one person, 2 engineers, 2 building inspectors asked about securing the logs between the roof and the foundation. 
I keep waiting. At my age I ony have to wait another 20 years. I hoping my luck holds out.  :D
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jake pogg

Quote from: Coastallogger on October 07, 2021, 02:18:53 PMI am about to start a log cabin in the Appalachian style: 2 sided logs, half dovetail corner notches...


Coatallogger,are you building just as is shown in that video,i.e. where the logs don't bear on each other laterally,but only at the corner notches?

For if so,i'm not sure i get the fastening schedule,where could you employ either lag-,or log-screws?

The more i read advice of Don P the more i appreciate it,there's comonly quite a bit more to it than meets the eye at first(Thank you,Don,for taking the time).

I can only agree with what Don says above:All-thread,continuous through the wall,is entirely eparate structural element vs fasteners in every course.

Concerning those,i'd personally not recommend installing Timberlocks,or similar,without pre-drilling And countersinking,they're infamous for hanging logs up.
I relieve the bore for the 1/4" Timberlocks with a 3/8" bit.

Concerning bubble-wrap,or Mylar film,or any of similar jazz,the important issue remains the vapor barrier.It's important that VB remains a single one,so that is why VB is not installed in the floors generally-the subfloor is normally a VB in itself.
And if/when the moisture does breach that for some reason,you want it to dissipate and not be trapped between the multiple layers of non-porous material.

I live in a climate where the floor is insulated to R-factor of 60(desirable),or 38 minimum.Refraction has only a miniscule value,more hypothetical than real.

The underneath of the platform will always need some solid protective layer.
It can be nailed shut using plywood,but that can actually cause problems with that very thing-the double VB.
If your joists are manufactured,as in TGI/BCI style,then tilting a plywood panel among the bottom flanges works well.
If solid,it may pay to nail a flange along the bottom of each for just uch tilting in of covering material.The future easy accessability of each bay is a distinct advantage.        
"You can teach a pig anything,it just takes time;but what's time to a pig?"
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Coastallogger

Quote from: Stephen1 on October 08, 2021, 08:19:09 PM
I keep waiting for my roof to blow off. We have had some great windstorms, but not the once in a hundred years. the roof is still here. I have waken up in the middle of the night hearing a great roar from the wind. It did not take me away.  8)
I had to have a permit to build my cabin.  Everyone was worried about the bottom course of logs being pinned to the ICF fondation wall. I have the bottom course secured, 1/2" treaded rod, just like they asked, and the SIP roof panels are screwed to the top log on the wall and ridge pole with 12" timber lock screws, just like the engineers asked.  Not one person, 2 engineers, 2 building inspectors asked about securing the logs between the roof and the foundation.
I keep waiting. At my age I ony have to wait another 20 years. I hoping my luck holds out.  :D
Ok here is the thing. With an overhang like yours, you have most of the wind acting on the roof, and only one course of logs holding it down, and it still doesn't blow away. 
So why would I (and also your engineers) worry about the house itself, where blowing off the foundation? That is where the vast majority of the weight is.
A 20 ft travel trailer weighing about the same as a single course of logs only (forget the weight of the loft attached to that course of logs and the roof itself) doesn't blow away either, even when you park it sea-side.
So given my same sized cabin weighs. Probably about 20 times more, why is everyone so worried about it being bolted to the ground as well? I can't imagine the sheer stresses that frost heaves would put on those bolts, and what it would do to the bottom course of logs themselves. 
I really appreciate your real-world experience with this.
Building 20X20 dovetail log cabin off grid.

Coastallogger

Quote from: jake pogg on October 09, 2021, 01:58:27 AM
Quote from: Coastallogger on October 07, 2021, 02:18:53 PMI am about to start a log cabin in the Appalachian style: 2 sided logs, half dovetail corner notches...


Coatallogger,are you building just as is shown in that video,i.e. where the logs don't bear on each other laterally,but only at the corner notches?

For if so,i'm not sure i get the fastening schedule,where could you employ either lag-,or log-screws?

The more i read advice of Don P the more i appreciate it,there's comonly quite a bit more to it than meets the eye at first(Thank you,Don,for taking the time).

I can only agree with what Don says above:All-thread,continuous through the wall,is entirely eparate structural element vs fasteners in every course.

Concerning those,i'd personally not recommend installing Timberlocks,or similar,without pre-drilling And countersinking,they're infamous for hanging logs up.
I relieve the bore for the 1/4" Timberlocks with a 3/8" bit.

Concerning bubble-wrap,or Mylar film,or any of similar jazz,the important issue remains the vapor barrier.It's important that VB remains a single one,so that is why VB is not installed in the floors generally-the subfloor is normally a VB in itself.
And if/when the moisture does breach that for some reason,you want it to dissipate and not be trapped between the multiple layers of non-porous material.

I live in a climate where the floor is insulated to R-factor of 60(desirable),or 38 minimum.Refraction has only a miniscule value,more hypothetical than real.

The underneath of the platform will always need some solid protective layer.
It can be nailed shut using plywood,but that can actually cause problems with that very thing-the double VB.
If your joists are manufactured,as in TGI/BCI style,then tilting a plywood panel among the bottom flanges works well.
If solid,it may pay to nail a flange along the bottom of each for just uch tilting in of covering material.The future easy accessability of each bay is a distinct advantage.        
Yes, this will be a chinked style. You can't do full scribe with a dovetail style corner joint. Gaps will open up anyways.
70-80 percent of the weight is on the corners, but you also have blocking at the windows and doors to keep the chinking gap constant.
Many people peg the courses at the windows and every 4 feet to keep them from twisting and to keep them in line. Thanks for your advice on the pre-boring. I will do that to be safe.
The floor system is still a bit of a pickle. I won't get the VB effect of a subfloor since 3/4 in plywood is 60$ a sheet where I am at the moment. Floor boards will be home-milled planks. And the joists will be boxed heart beams I mill myself. Probably limited to about 6-8 inches. Which is fine, because they are out of insulation any thicker than something made for 2x6s at every store in my area. Due to the everything shortage. 
So it would be nice with a thermal break on top of those joist beams that could double as a VB and get my insulation values up as 6 inches isn't close to code for my area. I don't haven't meet code, but I want a warm floor. My first idea was high compressive strength XPS Owens Corning pink stuff. That is fairly vapor impermeable. But it off-gasses. I did my basement with it, and it smells like a new car. I want my cabin to smell like the forest. I also have old stuff in my attic that turned brittle from off-gassing. It loses R value with age as well, which is to me totally unacceptable for where it is installed as it can't be easily replaced.
Foil faced polyiso doesn't off-gas and it is nearly perfectly vapor impermeable, but of course they also have no availability near me of that either due to the everything shortage.
So I came back to bubble wrap.
There is an unsponsored guy on YouTube who is in a similar climate with an off-grid cabin who has tried a lot of different things and swears by it. Keeps building more with it. His problem was critters and bugs loved to make homes in his fluffy insulations, but don't like the bubble wrap. Even I think Don P was fixing a place yesterday where the floor joists had to have work done to them due to bugs. I wonder if that had anything to do with fluffy insulation making the joists more habitable to bugs. That's why I am so hopeful there is an alternative given that a house in the forest has to deal with a lot of bugs. I figured worst case if it is bunk, I can add rockwool or fiberglass after the fact no problem and just deal with the critters if/when they come and consider it a trade-off for having warmer floors.
I didn't know plywood was so vapor impermeable. Thanks for that knowledge. I probably shouldn't cover it up with that then, as I am already short on R value in the floor. Better to keep it hardware cloth. Should at least keep rodents out, if not bugs.
Building 20X20 dovetail log cabin off grid.

Don P

Think in all directions. This stuff comes about in response to real events. We can brush off the laws of man but not so easily those of nature, keep your eyes and mind open. In uplift design you do account for actual dead weight offsetting the design uplift load.

Uplift, overturning and sliding are the typical failures. I'm not in earthquake country but we had a pretty significant tremor this past year. There was some overturning and sliding of things that weren't sufficiently bolted down. In some older farm structures the termites lost hold of one another and they just collapsed. Hurricanes and tornadoes often push poorly restrained buildings off foundations as well. Growing up just about every high wind event was accompanied by news of trailers rolling across the countryside, hence those strap kits being mandated. One memorable picture one of the APA engineers took after the Sunday of tornado's in the south was a 2 story house slid back about halfway on the basement foundation, step out the front door and fall in the basement. Well built it was relatively undamaged but the builder created a weak link, there were no anchor bolts to be seen. That engineer was part of the disaster engineering team that goes out after an event, figures out why things failed and ways to prevent those failures in the future. We are also exceeding the old design loads more often in places.

Talking to Dad after he had worked a flood down in TX they had come across a log home along a waterway that had raged, the foundation was a couple of miles upstream. He said it had survived the journey pretty much unscathed but was unrecoverable.

So anyway, I wouldn't forgo that "continuous load path". I'm not following the sill shear problem. How are you bringing in water and removing septic in frigid temps with a heaving building, in other words is there not already a piece of equipment on site going to that depth?

Reading this last post,  in the job we're on the termites had easy access to the building and it was too close to the ground. The chestnut sill we got to yesterday, although considered a highly decay resistant species was rotted and termite riddled, but also about a century old. The sills were white oak and chestnut, joists flattened white oak logs in drop in mortises, collapsing dry laid foundation so lots of decay, deflection, and fun  :).  An 8" deep joist probably isn't going to span 20' without a center girder, which, being under the building on dry ground will not behave the same as the outer ones that are heaving. If you are going to float I'd try to design to avoid a center girder and piers.

Coastallogger

Quote from: Don P on October 09, 2021, 09:39:02 AM
Think in all directions. This stuff comes about in response to real events. We can brush off the laws of man but not so easily those of nature, keep your eyes and mind open. In uplift design you do account for actual dead weight offsetting the design uplift load.

Uplift, overturning and sliding are the typical failures. I'm not in earthquake country but we had a pretty significant tremor this past year. There was some overturning and sliding of things that weren't sufficiently bolted down. In some older farm structures the termites lost hold of one another and they just collapsed. Hurricanes and tornadoes often push poorly restrained buildings off foundations as well. Growing up just about every high wind event was accompanied by news of trailers rolling across the countryside, hence those strap kits being mandated. One memorable picture one of the APA engineers took after the Sunday of tornado's in the south was a 2 story house slid back about halfway on the basement foundation, step out the front door and fall in the basement. Well built it was relatively undamaged but the builder created a weak link, there were no anchor bolts to be seen. That engineer was part of the disaster engineering team that goes out after an event, figures out why things failed and ways to prevent those failures in the future. We are also exceeding the old design loads more often in places.

Talking to Dad after he had worked a flood down in TX they had come across a log home along a waterway that had raged, the foundation was a couple of miles upstream. He said it had survived the journey pretty much unscathed but was unrecoverable.

So anyway, I wouldn't forgo that "continuous load path". I'm not following the sill shear problem. How are you bringing in water and removing septic in frigid temps with a heaving building, in other words is there not already a piece of equipment on site going to that depth?

Reading this last post,  in the job we're on the termites had easy access to the building and it was too close to the ground. The chestnut sill we got to yesterday, although considered a highly decay resistant species was rotted and termite riddled, but also about a century old. The sills were white oak and chestnut, joists flattened white oak logs in drop in mortises, collapsing dry laid foundation so lots of decay, deflection, and fun  :).  An 8" deep joist probably isn't going to span 20' without a center girder, which, being under the building on dry ground will not behave the same as the outer ones that are heaving. If you are going to float I'd try to design to avoid a center girder and piers.
Thanks Don,
So the stress I am talking about is if you connect the sill log to the pier, and the pier has frost heave act on it as to laterally shift the pier, the weak point would be the strength of the pier itself, the bolt, or the sill log, causing it to warp all failures that are very hard to fix. Frost is a virtual unstoppable force. And I have seen piers shift laterally and crack when fastened to the building where I am. For that reason, people who build in some of the colder climates have told me it's better to have the structure float on the piers, or have the "piers" themselves float. Unless you are qualified enough to be sure you are building frost-heave proof foundation, which even the pros mess up from time to time.
We don't have to deal with some of the the extreme weather the south sees. No tornadoes, no hurricanes, and it's not an earthquake zone.
So it sounds like the termites had nothing to do with the insulation. I am planning on building 18' off the ground, so I shouldn't have to worry about that. Although I don't have access to any rot resistant species. My land has almost only softwood, but some birch and maple. For that reason I am designing the joists to be easily replaceable without disassembling much. I know they won't last forever.
So I understand the only issue your client had with bubble wrap was it not keeping them as warm as they wanted, is that correct? If that is the only problem, then worst case, I just add the fluffy stuff later and deal with the bugs and rodents if they come. It still sounds like the best option I have available to be at the moment for thermal breaking the joists and vapor barrier at the moment at the very least. It will be designed with easy access to the bottom for that. I don't have any ideal options available to me at the moment given the shortages of building materials we are facing at the moment.
Water will come in by the barrel. Most of the water needs will take place in the bath house. The toilet will be in an outbuilding, showers will be in the bath house/sauna, laundry is in another house as well. The only grey water we need to handle will be carried out in a 5 gal bucket underneath the sink. So I don't have to worry about pipes freezing.
I appreciate your input on the joists. I had indeed planned on a center girder which will be 8x10, with 2 "piers" of their own supporting them along its length. But I hear you. They will settle differently for sure being further from the moisture of the outside. I hadn't thought of that. 
 
I could beef up the joists my online calculator shows I would need 2x12s for a 20 ft span with 16 OC. Maybe if I did them 8x10, 14.5 inches apart, with sleepers nailed in em, no girder, that would give me a similar stiffness as 2x12s. Fewer piers to shim and de-shim as it settles and potentially heaves as well, and easier since they are on the outside. 
Building 20X20 dovetail log cabin off grid.

Joe Hillmann

Quote from: Coastallogger on October 08, 2021, 05:46:46 PM
Quote from: Don P on October 08, 2021, 08:23:22 AM
It's been awhile since I checked priced but lags to structural screws was not a big material cost advantage, it was labor. When we did that for a living the structural screws were coming in towards the end. I would stock a few boxes of lags when we started those jobs. The withdrawal strength of a lag, its ability to pull ornery logs and timbers around, was higher than structural screws. If the log screws wouldn't pill things tight we would break out the lags.

On hanging up, divergent fastener angles, a trim nail, caulk on the vertical trim is an adhesive. Twist, binding log to fastener. Friction. Just remember shrinkage and settlement are 2 different things, hopefully related, but alas, not necessarily :D.

What are the issues with getting to frost depth and coming out of the dirt with masonry? Untreated foundation with a little flamethrower treatment and some fungi food applied is no match for soil borne rotters. You'll be revisiting that within a decade, probably with internal galleries up into the main structure.

I can't remember which of you was mentioning using bubble wrap. I had a client fall for that once, unfortunately on a million dollar home. If you feel warming going on it is because that thing is bleeding btu's. Only after the fact did I learn of the Federal Trade Commission's issues with their claims. Bubble wrap, foil or not, is a packaging material. It is a poor insulator and reflective barriers do have caveats with them.

Do remember when looking at alternatives that builders run in a competitive environment. If it is cheaper, easier, or works better for the buck you will see them adopting.  

Wow, that was a downer, well, better I guess to have the good and bad in mind. Gotta go unload a fridge so we can move it and drop a floor out from under it, the bugs had a party.
I made a reply to this earlier but it didn't show up here so forgive me if I am missing it and repeating myself.
Do I understand you right that the screws will lose their tension with shrinkage/settlement? In that case they won't make a replacement for allthread at the corners for transferring tension all the way to the bottom logs.
I think you have me sold on structural screw for keeping the courses in line, and the larger lag screws if those strip on a particularly twisted log as those have more biting power I hear.
The issues with going below frost line with masonry is the frost line is pretty deep where I am 6.5 feet or so. Which makes for a huge volume of masonry. Since I know little about masonry, and I am roughing it until I can move into my build, the extra time and money will be a buzzkill. Plus if I get something wrong, it's a much bigger headache to fix than floating "piers" where if I get ten years out of em before replacing, I will still probably have saved time and money by the time I die compared to masonry, even if I got it right. I am concerned about creating a "ladder" to the sill logs for soil-borne decomposers, but thought a capillary break on the top would be an effective barrier against that. I am reading borate works against fungi as well, but really mixed reviews on Shou Sugi Ban. But really it doesn't have to last forever since it will be so easy to jack a corner and slip a new one in. Would take a guy an afternoon.
It is me considering the bubble wrap. I am interested to hear what issues your client had with it and how it was put on. My plan was to put it in a continuous sheet between the log joists and subfloor, or between the subfloor and finish flooring. That would give a vapor barrier and provide protection against radiant heat escape. Then if that proves to be not enough insulation, the joists would be spaced 22 1/2 apart, so I can crawl under and put in rock wool sized for 24 OC joists, then cover it up with plywood and/or hardware cloth.
Then if the bubble wrap turned out to not be great at keeping me warm, at least it still serves as a vapor barrier and thermal break to help with thermal bridging of the joists.
The issues I hear of people who use fiberglass and similar under their log cabins is that critters and bugs love to nest in it. And it can be difficult to seal your insulation cavities perfectly since logs are constantly changing shape and size.
I hear what you are saying on best practices being best practices for a reason, but conventional best practices are formed in conventional builds, which is not at what I am doing. Also, being in the forest, there are more critters and bugs to contend with compared to a more sterile suburban site. A lot of log cabin owners complain that bugs and critters love fluffy insulation and steal it to make nests, or just take up residence there and eat away at your floor joists. The bubble wrap apparently critters want nothing to do with, which is a plus.
I understand as well that industry code and energy efficiency standards largely ignores the effect of radiant heat. It focuses more on the air temperature itself, but ignores that you can be much more comfortable in a cooler air temperature if you have radiant heat is being reflected at your body. This is why incandescent bulbs can actually save energy in a cool climate even though they burn more energy per lumen than LED. They slightly warm your body when you are near them with radiant heat, allowing you to be more comfy in cooler air. But they got banned. But I digress.
But certainly combining the radiant properties of the bubble wrap and making use of it as a vapor barrier/thermal bridge, plus using stuff with r-value like rockwool might be good.
All depending on your client's particular issues with the stuff which I am keen to hear.
Radiant barrier only works if ther is an air gap on at least one side of the barrier.  If the barrier only is reflective on one side the air gap HAS to be on that side.  If it is reflective on both sides the gap can be on either side.  If the gap is on the hot or cold side doesn't matter a whole lot.  But do you research to see which is better.  The gap is recommended to be at least 1 inch.
If there is no gap the heat loss is by conduction rather than radiation so the radiant barrier no longer works, and since it may be a good conductor it may cause more heat loss.

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