Finnish log cabin - logs and pegs

[davyoungnz]

Hi,

I'm looking into constructing a small log cabin. At the moment it's entirely in the theoretical stage of development - nowhere near the construction stage! 

I find the later Finnish log cabin construction quite appealing - flat walls inside and out; a centre partition wall that supports the purlins and ridge beam; and solid, pegged gable ends. 

Here's a little info on Finnish log house construction techniques:

https://forestryforum.com/board/index.php?topic=56387.0

https://forestryforum.com/board/index.php?topic=27608.0

Traditional Finnish Log House Building Process - 16mm Film Scan - English Version - YouTube

Now for a couple of questions... I'm sure I'll be back with more. Thanks in advance for taking the time to read this and/or answer.

Are the pegs used to minimise wall warpage exclusively made of heartwood? I've searched around but can't find the answer to this one. 

The Youtube clip above seems to indicate that the logs used in the construction of traditional Finnish cabins retain their sapwood - there are multiple instances throughout the film that appear to show this. Is this really the case? 

Cheers,
David

[jake pogg]

David hi,

Good job on research,indeed a big Thank you,i was not aware of those two threads that you posted a link to.

I was familiar with that museum restoration video,and it's also a wealth of very good info.

"Are the pegs used to minimise wall warpage exclusively made of heartwood? I've searched around but can't find the answer to this one. "


(i just screwed something up type-wise trying to copy&paste your questions)

NO idea about the nature of pegs barring that i've Just read in the first of Forum links you post.

I've just pegged a fair size house using 1 3/8" sq. pegs in  1 3/4" augered holes,the proportions are intuitive based on my experience with spruce.
I cut the pegs on a table-saw using the same species/vintage lumber as the walls,sopping-green White spruce.
Again,based on intuition solely,but i'd be careful assuming that pegging prevents twist:Conifers with great tensile strength such as White spruse are Very stubborn in their behavoir,what they want to do they generally WILL do,disregarding any attempts at mechanical restraint.

In this i'd pay particular attention to that museum video:It may not be very obvious,but the guys in the video exercise a Very stringent selection,(and a goodly doze of local-species knowledge)and that(i believe),is their safeguard in regards to twisting.


As to your second question i can say definitive Yes.As TW states in that first thread the trees up North are rather small(he's 63 deg. N,and i'm a touch under 65N,albeit in Western hemisphere(Alaska).
So definitely,heart-free-center cuts are Not an option for us,everything is used heart-centered. 

[TW]

1. The traditional material for peds is spruce undergrowth out of a dense stand of older tree. The undergrowth that suffers from shortage of sunlight develops very slender trunks with minimal knots and thin growth rings as they struggle to reach the light. Therefore such pegs are very strong. The normal diametre of the finished peg is 1 1/2 inch. Traditionally they were barked and shaved round to the correct thickness with drawknife leaving the hart in centre. The oldtimers marked the point where the peg was to be on the upside of the lower log and the underside of the upper log then turned the upper log upside down and drilled holes halfways through both logs and drove the log down onto the pegs.

In our modern time pegs are usually made from seleced boards of tight grained spruce. Not quite as strong as the old way. I use both sorts of materials depending on how great bending loads there will be on the pegs. As I have a joinery workshop I usually make pegs by the metre with octagonal section. 36x36mm octagonal for a 38mm hole. Then I can just saw the pegs to lenght on site and qickly chamfer the ends with a knife and drive them in. That saves a lot of time.
In our time when we have electric drills you normally drill the pegs through one log and into the next. It is easier to get everthing aligned that way. You always drill thge peg holes before adding any moss or oakum between the logs. The depth of the peg hole must always be measured and the peg be cut at least 7% shorter than the depth of the hole to allow for settling which is typically between 4 and 5 %.

The pegs are there to prevent the logs from twisting shemselves out of the wall and to keep long wall from buckling and to keep logs from sliding lateraly along each others when adjoining walls want to buckle. Older corner types were developed to withstand some twisting on their own and combined with careful selection of logs that meant that they could use fewer pegs. Later buildings have every log pegged down in both ends and sometimes in the middle too.

2. In certain isolated inland valleys in Norway they used gigantic trees for log walls in the old days. However in most places people considered it too laborious to manhandle such timbers around. Trees don't usually grow very large this far north and along the coasts and rivers the largest trees were in high demand for ship timber so it would have been wasteful to use them for log walls.
The normal wall thickness varies between 5 and 7 inches. 6 inches being the most common thickness for houses. For that you need logs at least 20cm preferably over 22 cm in top diametre under bark. The longer the better. 12 metre long logs are quite normal in old houses but nowadays we try to make do with logs no longer than 8.5 metres which is the longest one can saw on most local sawmills.
You saw the logs on two opposing sides to the thickness of the wall. Sawing saves a lot of labour compared to old style hewing. The natural taper of the logs is left as it is only the bark is removed from the round sides of the logs. The heart is in the center of each log and both heartwood and sapwood are used.

Since the second thread refered to was active I have learned quite a bit more and gained more experience so some detals I wrote about there are not quite correct as there are better ways of doing things.

[davyoungnz]

Hi Jake,

You're welcome and thanks a lot for your reply. Great to learn from someone with actual construction experience!

So at your latitude you have no choice but to retain sapwood due to the relatively small diameter of your trees. Interesting, I would never have guessed this. 

Thanks for sharing your thoughts around peg use. It makes sense not to solely rely on pegs to prevent warpage, especially with species like spruce, as you say. I take it you didn't exclusively use heartwood for your White spruce pegs; if you did you'd probably require a few trees just for pegs for that fair-sized house!

Cheers 

[jake pogg]

TW,thank you for your input,i'm really happy you're still around,and look forward to any and all info from you.

Yes,a peg cut from a pole would certainly be stronger,and this is how we peg a log-raft here when floating the logs down the river(if any distance involved).

The reason i used square pegs in a round hole was to limit the sideways loading,to avoid A,splitting moment,and B,any potential to hang the log up,to prevent it from settling correctly.

Our conditions here in Western Interior Alaska are close to yours,but colder and dryer(i'm about 300 miles from the salt as the crow flies,and there's no Gulfstream near that coast).
Indeed,there's some influence from the Scandinavian miners' building techniques still remains,from the era around 1860-ies to 1920-ies or so.

I've built a decent-size home using timbers sided on a vertical about 8 years ago.It made for a good home,however a friend for whom we built it is a bit disappointed with the checking,which is fairly severe in most logs.
The logs were 8"/20 cm thick,milled flat and scribed green,and stacked only the next year(ran out of time after disassembly on the off-site building site).Heated only another year hence,so everything happened Very gradually,yet the checking was pretty bad.
(could be our local spruce specifics).

From those old threads i was happy to see that you use Piilukirve,i imagine you'd probably be pretty hot with it by now,good for you!
(i only wish that i could get good with one,but not enough time in the season or help,i mill the flats on a band-saw and use an electric plane afterwards;no finishing after the logs are up other than break the glaze with abrasive disc+oil). 

Also was very pleased at your mention of the chinking with oakum,using a caulking iron and beetle.It's something i will have to do to the building i got up this past summer.
Do you ever treat your oakum with anything,or does it come treated?
(i'll probably be using some 3-stranded manila,about 3/8"/5 mm dia.,and on i think Don's suggestion was going to treat it with Stockholm tar diluted with turpentine.
Any thoughts?   

[jake pogg]

David,yes,that's correct.

There is the potential to use concentric sections of smaller dia. poles,either harvested green,or (like much of my materials caught drifting down the river),but my fear was their being overly tight,splitting the wall-logs in drying,and possibly hanging them up in settling.

Twisting-wise,the word on the street in N. America is that the Left-handed twist(as you look down the log the twist will go from you eather left or right) is no good-the US/Canadian Voluntary Log-Building Standards specify that such a log cannot be used in a wall other than maybe the first half-log.
The reason is that the left=twisted logs have Much more tendency to "unravel",to untwist and open up,vs the right-twist.

And the theory behind it is that all spruce trees are born twisted to the left,and begin to twist right as they grow.About their middle age they balance out to where we see them as "straight-grained"(in actuality it's always a double-helix).And the less common left-twisted trees Keep on twisting to the left,genetically lacking that tendency to compensate,and so are structurally inferior...

(all that is hypothesis,and in reality i end up using Many left-twisted logs as i simply lack sufficient choice to avoid them,alas).

I've NO earthly idea how it'd all work with Coriolis effect and all that!:) 

[TW]

Checking is not so much of a problem because the checks are all vertical and self draining in a hewn/sawn and scribed log wall. In a round log wall you will always have some checks sloping inwards so water can get in but not out.
Some fill the largest checks with oakum to improve insulation.

Traditionally they used moss between the logs when building. The moss had to be dried somewhat so it didn't schrink too much but not enough to make it fall apart. Then when the house has stod for a couple of years they caulked it with mallet and caulking iron.

Nowadays one can buy reday made strips of flax fibre insulation to use instead of moss in the initial stage. This saves time but I have used some moss now and then for repairs when nothing else was on hand. The flax fibres are not treated in any way.

The oakum for the final caulking is usually flax fibres and not treated in any way at all. Not around here. I have heard some rumours that they treat the oakum with Stockholm tar in some very weather exposed places in Norway but I don't know if it is true.
The long groove keeps the oakum surprisingly dry as the water drips off the outer edge.

I have been taught that logs whose top has rotated following the sun when looking upwards along the trunk of the tree are more prone to twisting later on. Such logs are better used for the short logs between windows.

The "first half log" is normally made not from a half log but from a small log that gets very small flat sides when sawn on three sides. A good place to make use of logs that are a bit too small to use elsewhere.

The interior of Alaska has a lot dryer climate than we have. Finland gets dryer the further north and east you go but here halfways up the western coast with the sea only a few kilometres away across the flat land we have a rather moist climate. What works here related to moisture should work with good marigins of safety in the Alaskan inland.

[TW]

Here you can see the extra notch on the inside of the corner which both counteracts twisting and makes the corner less draugh prone. With this roughly 3/4 of the height of the log is held rigidly from the sides compared to roughly half the height with an ordinary double notch or dovetail. In our local cialect of Swedish spoken on the coast of Österbotten we call the extra notch "varmtand".
The "varmtand" is generaly omitted in simpler outbuildings and sometimes in fine houses too if the logs aren't twisted.
The inland Finns had access to better timber and did usally not build with varmtand.

All types of dovetailed corners lack this extra precaution against twisting logs and therefore need lots and lots of pegs.

This picture shows the old version where the logs are (or have been) hewn hexagonal in the corners yet flat along the rest of the lenght. This is in a granary originally built in Vörå in the summer of 1693. The hexagonal hewing at the corner went out of use in the early 18th century around here. This building did not have a single peg in it except for the gables. As time progressed and methods improved pegs became more plentiful.



 

[jake pogg]

Thanks again,TW,for all this Very valuable info and your thoughts on it.

My building season over until spring,i took a trip with friends to some other areas of Alaska,and of course whenever possible looked at as many older buildings as i could.
Photos below are from an old Russian Orthodox church at the cemetery of a village of Eclutna,which is near the ocean,and several hundred miles south from my area.
The building is a little over 100 years old now,and was built using only hand-tools.
I could only access the outside,but i don't believe any provision such as "varmtand" was used to seal the corners.
All and all the quality of construction on this was so-so,the scarphs are of the most basic kind,and not much effort went into making the building "nice",more like bare necessities satisfied(life in AK was never easy,seasons even in that warmer region short,weather rough and unpredictable,labor always in very short supply.

They didn't skimp on pegging,i could see more than enough of fairly stout pegs where the logs separated(they were hewn polygonal pegs about 1 1/2" in dia.).

As visible in the photo the pins of that dovetail corner joint have separated quite a bit.
Some of that is due to twisting,but even without the twist,many features of such construction register the log above the log below-the lateral groove,the pegs,splines at openings,et c.
So,any part of the joint where the end-grain joins the side-grain must always eventually form a gap,i suppose...
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[jake pogg]

Scarphs along the long wall of that same building
(apologies for misspelling the village name,it's Eklutna):




 

[TW]

To me the Eklutna church looks like the sort of building you get when you are in a hurry to get something built in a new colony with unskilled labour.
Or it could be built by Russians. In large parts of Russia farmers lived in serfdom until the 1860-ies and as the serfs owned nothing and were bought and sold like cattle they had learned not to waste effort on building anything better than absolutely necsessary as it may be lost tomorrow to a whim of someone higher up in the pecking order. That heritage of oppression can be seen in Russian homes to this day.

Those primitive scarphes all on top of one another would not be accepted in a farmhouse in Finland. Not in a new building. I wonder if the church has been extended or maybe shortened at some point because in such instances one may find emergency fixes like that.
The normal way was and is to spread the scarphes over the wall so two never came on top of each others. Scarphes are usually made only where one can anticipate tension stresses. Elsewhere a tongue and groove joint in end grain is better as it doesn't open up if the logs twist. A peg into the log below on each side of the tongue and groove joint prevents the two logs from being pulled apart.

All side grain to end grain joints are bound to open up a little. It is unavoidable. That is why many insulated buildings (not all) have a "mosahugg" which is a v-shaped groove cut into the end grain on the inside of the corner notch and stuffed full of moss from above before the next log is added. As the gap opened the moss expanded.
This is also the reason why most of our local dovetailed corners have one or another sort of step in them so that a log sliding outwards meets a positive stop instead of wedging the joint apart.
My grandfather who was a very thorough carpenter working in the last twilight of traditional log buiding when everything had to be simplified and rationalized to the utmost he used simple dovetails without any sort of step. Though with them he prefered to use timber that had dried for one and a half year after sawing and he drove a 5 inch nail into the corner for every course as an extra reinforcement.

[jake pogg]

Wonderful info,TW,yet again i thank you for providing all this data,i think it's super valuable(and very rare).

I totally agree with your analysis of the why's of this church,both the Alaskan part of it(too little/too late/scarcity of labor and resources),and of course Everything Russian-half-a$$ historically(and worse even today,alas).

I'm beginning to feel bad for kinda highjacking David's thread...Hope that all this stuff will be helpful,David,for your planning?

[TW]

Feel free to ask questions David and I will answer to the best of my knowledge.

[davyoungnz]

Hi Jake and TW,

Thanks a lot for well and truly answering my questions and providing a wealth of information on a myriad things I never even considered. Don't worry, I don't feel you're hijacking the thread at all! 

With all of these new things to consider, I can't help but formulate more questions... 

You both mention "half logs" - are you referring to the uppermost wall logs required on two sides (of a rectangular cabin) to level the tops of the walls?

While splitting the wall logs is a grave concern, I do find the traditional peg construction method quite appealing. Are they traditionally fit snuggly or loosely? What's the typical base diameter of the spruce poles traditionally used for fashioning pegs? At a metre long, I imagine you'd only get 2 - 3 pegs per tree.

Thanks for providing a photo of the 'varmtand' corner joint - this really clarifies things for me. From what I understand, the depth of the standard double notch is about a quarter of the log height (per notch). The varmtand notch looks to have a depth of about 1/8 of the log height (half that of the double notch). Is this correct?

The amount of information this thread already contains is quite something. Thanks enlightening me in the art of log home construction and history - I'll be rereading this material for some time to come.

Cheers,
David

     

[TW]

Jake refered to the American habit of sawing logs in half and starting with them on two walls to get the height difference you want when starting from a lever foundation. Our way is to put the smallest logs in the heap as first course on the shorter end walls and the biggest logs in the heap as first course on the longer side walls.
Though on simple outbuildings that just sit on a few boulders you let the underside of the building be uneven.

There is no need to make the top of the building even. As you add log course after log course working your way up you keep minding that oppisite walls are equally high and that the top of the logs always is a bit low providing room for the butt of the log above. If a log is too high somewhere to allow for proper scribing on waney edges you just cut away a little material from the round side with a chainsaw and shave it smooth and rounded by drawknife. When you approach the plate you think ahead so that once the plate is in place it's top side will be rougly even. On the end walls you then fit the first log in the gable.

The pegs fit snugly but not snugly enugh to split the log. Therefore I have found an octagonal shape to be best. They are stronger than square pegs yet less risk of splitting the log than when using round pegs. The corners of the octagons are compressed when driving in the peg so you get a tight fit without cracking the log. I use a large two handed plastic mallet for driving the pegs in and using it they should slide in fairly easily.
The spruce poles are only large enough to yield the peg you want. Or a little thicker. The sapwood has the treatest elasticity and greatest bending strenght so when you are after strong pens you look for poles that are just oversize enough to be cut into the octagonal shape.
The lenght "per metre" refered to that I make them whatever lenght the material yeilds between large knots and other flaws. Usually less than 3 metres though.

I will make a drawing to show how the corner notches are measured.

[TW]

A picture of how a log that was found to be too high to fit into the adjoining log wall is cut down to height. The bulk of excess timber is removed with chainsaw or axe and then the top side is made round and smooth either with electric hand plane or drawknife.
This is very common in repair work when the hight of each log in the adjoining wall is given beforehand. It sometimes occures in new builds as well that the height just doesn't fit in the corner or there is not enough waney edge to scribe in.

[TW]

There must always be enough room for the scribe to that the scribe line that defines the dge of the long groove doesn't run out onto the flat of the log. With our knotty and often a bit crooked trees here at the coast it means that you often have to shave down the round side of the log in some spots before scribing.


 

[TW]

A log ready for scribing. The nothes are cut just deep enough to bring the log down so that it can be scribed


 
The scibe fitting process in a sort of paralell movement where all vertical measurements are set out with the spirit level (plumb board in the old days) with reference from the logs below and all horizintal or slanting surfaces are transfered with the scribe set at the same depth all along the log.

[TW]

The protruding log ends are scribed but you don't cut any long groove in them. Instead you cut flat surfaces straight across with the scribe lines as guide. You cut a little past the line so that there is a horizontal air gap of roughly 5 mm between the log ends. This is to ensure that even after a rainstorm when the rain has lashed the log ends and made them swell more than the rest of the wall they do not end up carrying any weight.

In inland areas where the climate is less windy and less wet they often cut the long groove i the log ends too but in our coastal climate it doesn't work at all. The log ends crack and crumble when they swell and come to take up the weight of the house.




In the notch itself you also use the log scribe to mark the final depth of the notch. However you immediately move the mark between 5 and 10 mm upwards to ensure that the corner notch never ever comes to carry any weight even if the long groove is deformed a bit. The long groove is to carry the weight because the weight makes it tighter.

I think I made it through the explanation without drawing.

[Don P]

TW, this is great. Do you happen to have the "next" picture after this one, of you scribing?

[TW]

TW, this is great. Do you happen to have the "next" picture after this one, of you scribing?

Dad may have some pictures but I don't. I was busy scribing. Someone else may have taken photos though.

To the left is the log scribe. It is adjusted by moving the ring back or fourt and wedging a woodchip between the shanks. The normal scribing tool for most log building work.


 
To the right are the dividers with outward pointing tips which I use for scribing the sloping notches for old style hexagonal logs and for scribing the corners of simple round log sheds.

[jake pogg]

Thanks,TW,excellent thread,i'm enjoying this immensely.
Wish i had read some of this a few months ago as i was starting the latest cabin,but them's the breaks.

Among other points I especially appreciate that mention of how region-specific much of the technology is,and how under some other conditions the technique would be somewhat modified.

It's an important reminder of how much of critical thinking goes into log-building,that there's most often a very solid reason for this or that choice of approach and so on.

Lovely old tools there...I've forged a traditional scribe like that for a friend once,but have never used one myself.I presume that to use one the log would already be some ways down in the corner notches,"pre-scribed" if you will,as the distance between points is not that great(compared to a scribe with a set of bubbles that can be used on a much wider setting)?

Another somewhat unrelated question,if i may:On the photo below there're several strands where the grain is darker and wider-that is "compression wood",where the cellulose has grown thicker because of some environmental stress(like the ground falling away and the tree gradually adjusting,straightening itself back to vertical).
Such thickened cell-walls are nearly twice harder than the surrounding wood,and often have the power and tendency to distort the log in some surprising ways.

I was wondering if that's common in your area,TW,and if it is if it's an issue during selection process for you guys(that pattern is especially obvious on the cross-grain cut).





 

[TW]

Aye that's correct. You cut the notches in the log to be scribe fitted just deep enough to let the upper log touch the lower log round side against round side before you start scribing. As the scribe is held vertically by eye the shorter the distance between the points the less error will be caused by it being a few degrees off from vertical at times.

My grandfather's scribe has only two arms but I found that theese older scriped with a pair of arms pointing outwards as well are much easier to keep vertical by eye.
I have never used one of those canadian scribes. I imagine they could be handy for the corner notches on round or hexagonal logs. A bit costly for me though. I once saw another carpenter using one which he had ordered from Canada.

All of this is very region specific. I work in is the tradition of the Swedes in Österbotten on the western coast of Finland. Our ways are a mix of the methods used by the Finns further inland and the methods used on the nearby coast of Sweden. Plus some local adaptations.
I can tell by the way they work that the film at the start of this thread is from the region of Savo in south eastern Finland.

That compression wood is called "tjur" in our dialect. If there is a lot of it I avoid using that log. However our local spruce sometimes has just a few darker growth rings that usually means very little. One adwantage with sawing (or heving in the old days) the logs on two sides in advance before starting the build is that one can see if the log wanted to twist or bend too badly after sawing.

[davyoungnz]

Thanks again for the abundance of information, TW. I'm currently grappling with visually/spatially conceptualising it and how to put some of the principles you've outlined into practice. The logic behind the construction techniques in the video I posted at the beginning of this thread is much more apparent now. You've even taught me the word 'snugly'! I mistakenly wrote 'snuggly' when referring to the fit of the pegs; snuggly means warm and cosy, not tight-fitting...

I quite like the joint used in the video I posted at the beginning. Could this joint be considered a variant of the varmtand joint? It seems that the characteristics of this particular joint would minimise twisting of the wall logs and draughtiness, much like the varmtand joint in your photo. I've included a drawing of how I perceive this joint, but I'm unsure if I've fully understood it. From what I can tell, the bevelled faces of any one log mate with those of the adjoining log(s), and incidentally, I believe the bevelled faces are the key as to why this joint would resist twisting forces. However, once again I'm unsure if this really is the case. Would it be advisable to use this joint with green wood provided the notches are over-scribed somewhat to accommodate shrinkage?

I noticed that the logs in the photo with the ladder leaning against the scaffolding (post #17) have their faces scalloped out around the notches. What's the purpose of these cuts? I haven't seen them used in the construction of flat-sided log walls before, but have seen them in the context of round log construction and assumed that they make scribing somewhat easier.   

Just thought I'd share another video demonstrating the construction of the standard double notch. In my unseasoned opinion, I think it does a good job at demonstrating some of the techniques you've mentioned. 

https://www.youtube.com/watch?v=GI0sJOcY7ow


Cheers

[TW]

The youtube film seems to be from Estonia. The intro text was in Estonian and one of the axes was disticktly Russian and the other most likely from the Baltic region. Down there ash is rather plentiful and hence they don't traditionally forge collared axe heads. Even a shorter eye holds the axe head steady on an ash handle.
They did a good job showing how everything is measured. Even those millimetres you add to the setting of the scribe when laying out the depth of the corner notches.

To be continued