Building log cabin with green logs

[barbender]

I don't like the idea of screws as they can cause settling problems. If you provide relief for them, unless you have springs under them they're not providing any "hold down". On hand scribed log homes, wooden dowels provide the lateral resistance. So will the window and door backs you install. If you want something that will resist uplift, threaded rod that goes all the way from the top plate to the bottom plate is the way to go.

[Banjo picker]

And if you are like me and too cheap to spring for the whole threaded rod, you could do this...top and bottom.

bottom is hilted in with epoxy.  Banjo

[Don P]

Thanks everyone! Would anyone know about the shrinkage in that? Like would my logs individually separate some or would the entire wall just shrink together? I really appreciate all the positive feedback! How would I go about putting my roof on if the walls shrink and windows etc.? Again thank you all!

Some things to think about. It's going to sound like I'm being fussy but bear with me for a minute and think about what is going on. Shrinkage and settlement are not the same thing. Shrinkage is the wood shrinking as it loses moisture. Settlement is the logs moving downward, in response to shrinkage. But settlement can be caused by more things going on. In a scribe fitted home like firefighter's there are a few more things causing settlement, compression of the thin edges of the scribed lateral joints. Those edges are bearing on tangential grain which has about twice the shrinkage of radial. The coped laterals spreading as the check forms in them, also called slumping. For anyone interested you can find all of this described in more detail in the log home standard.

The 1/4" per foot I mentioned is from the prescriptive radial settlement table in that standard, for a milled white wood log in a warm humid climate drying from fiber saturation point, green to dry.  Can you go more, in most cases it doesn't hurt anything. During the development of that code a number of us wrote in to disagree with the logic behind that table, in the real world the settlement is actually less. Why. First, the settlement allowance is based on shrinkage data from the USFPL. Those shrinkage numbers were based on very thin radial and tangential samples, free to move in response to moisture changes. A full sized timber doesn't shrink as much as a piece of veneer because it is somewhat bound internally by differing stresses and rays. Second, when a check forms the wood has indeed shrunk but the dimension of the timber has not changed as much as the amount of shrinkage. Part of the shrinkage is in that check.

Will your wall shrink uniformly, all together and remain perfectly tight or will there be some separation. There will probably be some separation. For one the shrinkage numbers are averages, each log is an individual and will shrink somewhat differently. Not all will be straight grained, some will twist to a greater or lesser degree. Some will have knots, ever notice in a dried board that the knots are proud, longitudinal grain perp to the axis of the board.

To settle around a fastener, any fastener, the rows of fasteners need to be plumb. If they wander around at divergent angles nothing is settling. If a log twists as it dries it is certainly going to put friction on the fasteners before allowing any settlement. Can a 2500 lb spring overcome the twist and bow of a large drying timber? Can you stack an entire wall of such timber and then successfully tighten it all? Will all members be in plane? One group of chink builders intentionally builds log homes that do not settle. They drive rebar at opposing angles from row to row to lock the height. The logs shrink individually but are hung in place on the opposing pieces of rebar.

The roof springs from the top course of the log walls, assuming it is only bearing on the logs, as they settle the roof is simply along for the ride. As long as the logs settle somewhat uniformly and that it isn't tied to something that doesn't settle, like a chimney, the roof remains in plane.

[Nsp0005]

Yeah that’s why I’m doing butt and pass method to avoid that. 

[pappy19]

Why not just use standing dead? I used standing dead Idaho white pine and have lived in our log home for 18 years. Swedish cope round logs, 3 stories and no movement whatsoever.

[arky217]

Some of my logs are over 40 feet long and maybe 20” diameter at the big end.  There is almost no visible checking anywhere in the house.  That is because of the saw kerf that is run down the middle of the joint.  I would look for a foam gasket that has adhesive on one side.  Place that close to the inner edge and close to the outer edge.  When the house is done, use a caulk like Big Stretch and run a bead along the outer seams and you should not need it inside.

(Image hidden from quote, click to view.)

I'm building a small (12'x12') log cabin out of green southern pine using sort of the same strategy.
Using approx. 10" logs, I'll be milling 3/4" off the tops and bottoms.
This leaves the log 8.5" thick with a 5.5" wide flat on top and bottom.

Then I'll cut a kerf 3.5" deep on the bottom to help prevent checking. I'll use a modified butt & pass
method in that I'll drill a 1/2" hole thru the top log and 5" into the bottom log. Then I'll enlarge the
hole in the top log to 5/8".

Then I'll drive a 13" length of 1/2" rebar so that's it's recessed 1/2" into
the top log. This way the rebar will be tight in the bottom log and will allow the top log to settle and
stay snug to the bottom log.

But I have a question about using a 1/8" thick x 5.5" wide strip of sill foam between the logs.
I plan to lay down the strips as I assemble the logs since the logs should stay snug to each other
which would make it hard to wedge in the foam strip after assembly.

But the question is, will the foam strip hinder the purpose of the kerf cut by sealing it off.
Perhaps I should forget about the foam strip and just caulk the outside joints after assembly.

I would like to use the foam strip but not at the cost of checking.
What do you think?

[Don P]

Foam really needs somewhere to live to be able to recover. It doesn't recover if smashed flat. You also don't really want it creating dimension.
Centered on the bottom flat, straddling your kerf, run a power planer a couple of passes up the length of the underside of the log, creating a plowed out wide, shallow groove. Stick the foam in that, then it doesn't interfere with log height and the foam is not crushed. Flat faces  become convex as the timbers dry, this will keep the logs bearing on the outer edges of the plowed groove. Fastening the logs down with screws in counterbored pilot holes lets you get them tighter to begin with, something I've never been able to do with any dowel type connector, pins, spikes, rebar. At least take that out of the gapping equation. Allthread drilled in as you go can allow you to keep tightening the stack later.The foam will not prevent the drying stress from concentrating on that weakest radial part of the log, it is a stress concentration point rather than a drying point.

[arky217]

Foam really needs somewhere to live to be able to recover. It doesn't recover if smashed flat. You also don't really want it creating dimension.
Centered on the bottom flat, straddling your kerf, run a power planer a couple of passes up the length of the underside of the log, creating a plowed out wide, shallow groove. Stick the foam in that, then it doesn't interfere with log height and the foam is not crushed. Flat faces  become convex as the timbers dry, this will keep the logs bearing on the outer edges of the plowed groove. Fastening the logs down with screws in counterbored pilot holes lets you get them tighter to begin with, something I've never been able to do with any dowel type connector, pins, spikes, rebar. At least take that out of the gapping equation. Allthread drilled in as you go can allow you to keep tightening the stack later.The foam will not prevent the drying stress from concentrating on that weakest radial part of the log, it is a stress concentration point rather than a drying point.

Very good answer; thank you.
I like the idea of using a power planer as you suggested;
I didn't realize that the flat surfaces would become convex as they dried.

Another thought occurred to me about my intended plan on enlarging the hole in the upper log
so that it will settle down on the rebar as the logs shrink.

I intended to redrill the 1/2" hole in the upper log to 5/8" to accomplish this,
but what with the possibility of the logs twisting or otherwise deforming as it shrinks,
I now wonder if I should increase the size of the hole in the upper log to 3/4"
to make sure the upper log will stay down on the lower log and not bind up on the rebar.

What do you think ?

[Don P]

The convex flat surface is a result of the shrinkage difference between radial and tangential grain. Tangential shrinkage is about double radial. The center of a boxed heart timber is radial and the outer edges are tangential grain.

If the rebar is free in the upper log and there is no "head" on the fastener... what is it doing? It isn't helping to draw things down during assembly or holding down a twist, and it isn't helping with uplift. Is this just a loose lateral restraint? If you want to hold the upper log down on the lower log I think you'll have more luck with allthread from bottom to top in loose holes with a big plate and nut top and bottom. I doubt you can crank the entire stack down fully tight but certainly much more than just the weight of the stack.

[Stephen1]

One other item to think about is the length of your wall. From what I had studied when I built my place was no log wall should be longer than 20' as they have tend to spring out, or in. An interior wall or a corner is recommended. It might also be different with rebar or log screws every 2'
DonP might weigh in on that.
 I was told at the time that 3/4' shrinkage for every foot of wall height. 
DonP I understand after reading your post what you are talkiing about with the flat logs. Mine is A scribe home so a height shrinkage rate is increased.