Heavy timber truss.

[D L Bahler]

And along the same lines, justa few kilometers away is Schloss Spiez, a somewhat younger castle but still quite old.



                              

Connected to the castle, within the protective walls, is also found the 1000+ year old church, built in a Romanesque style and little changed since it was first built.



 

[D L Bahler]

Last one,

This time Schloss Trachselwald, in the Emmental.

This castle is famous for serving as a prison for the Anabaptists during the past 5 centuries until religious freedom was granted in the Canton of Bern with the constitutional reforms that occurred during the 19th century. Which brings up why I visited these castles. Thun, Spiez, and Trachselwald are all places where my own Anabaptist ancestors were imprisoned and, at least n the case of Thun, executed. So needless to say, these pictures have a lot of meaning to me. But that's beside the point of this topic.


Here are some pictures of the roof of Trachselwald castle, to observe another example of this unique and very impressive form of very heavy truss framing.

And as always, an exterior view to put the framing into perspective...



  

  

  

  

  

  

  

  

 

The last 2 pictures detail the framing of the covered walkway that leads up the hill to the castle mount.

The 3rd to last picture details some framing of the covering over the ramparts.

[timberwrestler]

Dave,

The Guild's review of historic trusses is also a good resource (pdf links on the left):
http://www.tfguild.org/publications/guild-books

B

[Dave Shepard]

I have that somewhere, boxed up from the move probably.

Have you tried any of that locust peg stock?

[S.Hyland]

We have seen so many great truss pictures, but how about a un truss? I saw this the other day on the front of a lumber yard. At first glance I thought it was a king post truss.

  

  

 


Then I realized there is no truss there at all. The "kingpost" and the bottom chord don't tie into the rafters at all. Instead, the rafters just sit on the three plates. This means that the 25' beam which would have been the bottom chord is actually supporting that top plate. This problem is further compounded by that "swoop" on the bottom that reduces the pine 8x10 to a 8x7. It left me shaking my head.
Am I crazy or is that thing totally wrong structurally?

[Jay C. White Cloud]

Hey Sean,

Your not crazy at all.  When I see timber frame work like this, I kind'a shutter and just shake my head.  If a P.E. signed off on it, good for them, if not, then I'm even more concerned.  That is why I know I stress to folk here on the forum if you don't have at least 20 years in the timber wrighting trade, with the experience to go with it, have your work check out by a PE with timber framing experience.  I would love to stretch a string across that tie beam each year, just to see if it is slowly sagging.  Is it strong enough, probably so, but would it meet standard for "moment deflection," in commercial building application, I doubt it very much.

Unfortunately, this is becoming all too common, as inexperienced folks try to jump into the "timber framing wagon."  I just recently learned of two contracting companies that are advertising timber framing since they couldn't get enough work "stick building."  Longest tenon on their frame I saw was only 4.5", not very much holding the frame together but stress skin panel and foam.  I'm scared to death about it, because it reflects badly on the rest of us.

Regards,

jay

[Rooster]

Or...just have the engineer or builder use it as a carport, and park his fancy "horseless carriage" under it...then we'll see if it was a good choice to build it that way...eh?

Rooster

[Jay C. White Cloud]

 :D :D :D NIMB would be the response... :D :D :D

[beenthere]

Maybe what is actually there is not visible to the eye.

Maybe rather than allude to the problem, point it out for us. 

Not obvious from the pics, as I see them.

[Jay C. White Cloud]

Then I realized there is no truss there at all. The "kingpost" and the bottom chord don't tie into the rafters at all. Instead, the rafters just sit on the three plates. This means that the 25' beam which would have been the bottom chord is actually supporting that top plate. This problem is further compounded by that "swoop" on the bottom that reduces the pine 8x10 to a 8x7. It left me shaking my head.

I think Sean did a really good job with his original post pointing out the error in this frame assembly.  What appears at first glance to be a king post truss assembly, after looking closer, clearly isn't.  What else is there to explain?  The only thing I could add to Sean's observation is that you can see this is a common rafter system, with it's weight bearing onto the ridge and rafter plates, they (rafters) tie nothing together.  This would be called a "hung Roof."

Regards,

jay

[beenthere]

White Cloud
Pls try again.
U seem to be talking around an issue, that from the pics shown are not obvious (at least to someone without 20 years of timber framing) so please help me (maybe others too ) out.

Where will this frame fail if under a snow load for example and why. 

[Jay C. White Cloud]

Beenthere, et al.,

My mistake, sorry if we (Sean or I,) had not been clear.  I will break it down, and you let me know where it still seams weak as an explanation:

The photo shows a "False King Post Assembly," for the following reasons:

1.  You have a Tie Beam that is reduced in the center too much for the span from just visual assessment.

2.  The King Post is holding up a Ridge Beam that is in tern taking the load of all the common rafters and the "Pseudo-principle Rafters" as well.

3.  The foot of the "Pseudo-principle Rafters" is not sufficiently housed-joined at either end to form a true truss assembly.

4.  The "Struts" in the assembly do not appear to be doing much work and not in the manner they would be in a real "King Post Truss" assembly.

If there is hidden metal fasteners it could strength the frame, but would still not make it a truss assembly.  Is that a little better?

Regards,

jay

[beenthere]

Is that a little better?

That's some better.
I'm thinking there are some metal fasteners that cannot be seen, thus my concern for the "thumbs down" comments.
I also (if I was doing it) would have a steel tension cable or rod that is imbedded in the Tie Beam pulling (keeping) the King truss from spreading and for supporting the ridge beam.
Then the necked down tie beam would not be a problem as I see it. Whether they constructed it that way, I don't know and assume we can't know if from just the pics.

My point for raising any question was the "thumbs down" without really knowing more about the design and construction.
Thanks for sharing your info.

[S.Hyland]

My main issue is that with no additional wood, labor, or metal fasteners, a functional timber truss could have been built instead. It just displays an indifference to the craft. It is made for looks, not for long term structural stability. The sad part is that this was not the work of a newcomer.  This guy has been in business since the late 70's, with this being pretty representative of his work. Some people approach this as a craft, others market product. 

[Jay C. White Cloud]

I'm thinking there are some metal fasteners that cannot be seen, thus my concern for the "thumbs down" comments.

Just to let you know how silly I can be Beenthere, I went back several times looking for a "thumbs down," symbol some place on the post, till I figured out what you meant... :D :D :D I'm to literal sometimes.

I also (if I was doing it) would have a steel tension cable or rod that is embedded in the Tie Beam pulling (keeping) the King truss from spreading and for supporting the ridge beam.

I can respect forged elements in timber framing, (and by today's standards, making it Post and Beam) if the metal work becomes an integral part to the work.  When done well it actually makes a statement and is aesthetically pleasing.  What I don't care for, (and other timber wright, designers and architects have shared the same sentient with me,) is Faux work, Such as Sean shared with us on the store front.  If your going to build a "king Post Truss," then build a real one.  There is absolutely no need for metal fasteners or hardware of any kind.  If do to moment deflection, or other load criteria there is a need to enlarge a member or reinforce a point in the roof/wall diaphragm with hardware to meet PE specifications for public structures, so be it, but the frame itself can more than stand alone with out the hardware if done properly.  The one shown is misleading.  If you do not have the skill to design and build it, then do as you suggested and build a Post and Beam assembly with cables and metal straps.

This may seam harsh but in reality it isn't.  Timber framing is not difficult to do correctly and even easier to do badly, or in this case "falsely."  The false hood leads others to believe that is the way something is done, and it isn't.  I have, now in my career as a timber wright, come in after a frame is built incorrectly and failing in someway, to fix it, way to often.  If I get the rare chance to ask why this happened, what I often get is, "well that is how I thought it was done," or "that is the way I saw it done."  I cross over jobs like this at least once a year on average.

My point for raising any question was the "thumbs down" without really knowing more about the design and construction.

If I seemed to have given the impressionism that I was giving this store front timber frame a "thumbs down," I'm sorry.  I even said that if the frame was signed off on by a PE, that all is good.  However, IMO this is "faux," work and reflect poorly on the craft.  I would have felt much better about the work aesthetically and in design if there had been metal strapping and visible reinforcement rods.  They could have been done in such a way that they would accent the work and support the reality of the work they do.

Regards,

jay

[chainsaw_louie]

Here is one that is a lot older than that, but it too defies the imagination to understand just how it stays up :

There is a lot of weight there and its hung at least 15-20' feet off the face of the building.  Bldg is in Fairmont park , Phila.

[jueston]

that is just amazing....

[D L Bahler]

Longest tenon on their frame I saw was only 4.5", not very much holding the frame together but stress skin panel and foam.  I'm scared to death about it, because it reflects badly on the rest of us.

Regards,

jay

Jay,
Just thought I'd point out, in those Bernese farmhouses I showed, you know with the huge trusses in the hay loft, often times the longest tenons ever used are about 2 inches. And some of these buildings have stood hundreds of years. They are definitely built to last. Those huge Medieval Castle roofs? Ya, those are built with stub tenons and extremely simple joints.

The difference is the focus of the joinery -for example a mortise and tenon is NEVER used in a tension joint, and the almost non-existence of any kind of level joint assembly -timbers are stacked and lodged.

The truss in question actual COULD work, but not as executed. I've seen assemblies a lot like this in Bern, all over the place. Just a few tweaks need to be made to redirect forces more efficiently.

I think louie's example is a similar principle, can't tell if it has a ridge beam but it does appear to.

But I undesrtand what you are saying, on an English style frame, you need longer tenons to work. But I have to wonder, if I would take you to the workshop of a Bernese carpenter, would you be horrified by the smallness of all of their joinery?

The master carpenter I learned from told me, pretty much always tenons are 1 1/2 to 2 inches in length, everywhere from walls to roofs. The exception being the Alemannic sill, which employs a large double through tenon assembly, wedged in place.

Also, generally pegs are never used. The emphasis of the design is to place all members in compression, whenever possible. When tension exists, lap, cog, or dovetail style joints are used. Not tenons.

[Jay C. White Cloud]

Hello Chainsaw-Louie,

What a wonderful post with pictures. That is some beautiful architecture (Gothic Revival and/or Stick style work circa 1840-1890.)  It is truly amazing what they pulled off with the cantilevered bracketed roof supports in these two styles of middle or so nineteenth century architecture.  Thanks for the post!


Hi David,

I did know that David, but thank you for sharing more detail of your passion for this region's architecture.  "Bernese Oberland" folk architecture, particularly the farmhouses you have shared, aren't categorized as timber frames in general as they are log structures.  Now, I have debated with many of the years that the difference between Log and "All timber" architecture is not that different, especially when it comes to the roofing methodologies.

Similar architectural styles (i.e. Alemannic, Walser, etc.) rely heavily on compression systems of joinery that can work very well with shorter tenons, as they are also "infill" architecture, as are many of the "half timber" work of Europe.

Those huge Medieval Castle roofs? Ya, those are built with stub tenons and extremely simple joints.

That is not quite the case as many of these structures rely on some pretty sophisticated "passover lap joints" and extensive "strong back" bracing in their roofs, particularly as you move West in Europe, France for example.

The difference is the focus of the joinery -for example a mortise and tenon is NEVER used in a tension joint, and the almost non-existence of any kind of level joint assembly -timbers are stacked and lodged

. If you are referencing your "Bernese Oberland" styles, I would say that is about 95% ture in most cases, but not in the body or history of timber framing, such as the OP's query about "heavy timber trusses.

The truss in question actual COULD work, but not as executed. I've seen assemblies a lot like this in Bern, all over the place. Just a few tweaks need to be made to redirect forces more efficiently.

I believe the truss in question would take a tad more than some basic tweaking, but that is just my assessment.

I think louie's example is a similar principle, can't tell if it has a ridge beam but it does appear to.

Louie's Gothic Revival example would most likely have a ridge beam as this was common practice for both Gothic Revival and Stick style architecture, but it is not a "truss system" and would more commonly be referred to as a "hung roof" transferring it's loads to the ridge and rafter plates, then down through the brackets.  Now what you can see in the photo that probably exists, as it was common practice during that period and style are the hidden metal straps and rods that are probably lock the gabled pent to the stone superstructure.  This work probably relies on both wood and steel joinery. This " cantilevered pent roof" style is very rare and was wonderful to see.

[D L Bahler]

Jay,
referring not to the Oberland Blockbau, rather to the Timber framing of the Swiss Plateau. This is truly West Germanic timber framing, not log construction. The framing of the Berner Mitteland was my first passion, my family comes from one of those huge Bauernhauses in the Gürbetal region, the Farm Grund in the village of Kirchethurnen is my ancestral home, the nearby village of Wattenwil is the Heimatort of the Bähler family. (This to demonstrate that I have been steeped deeply in this stuff from my youth)

And the castle roofs I was talking about were specifically those shown from Thun, Spiez, and Trachselwald in the Canton of Bern. I cannot speak regarding the Castles of France, England, or anywhere else as I have not studied them in person.

And I was taught that in the Lower Bernese (That is, the Bernese lowlands, north of the Alps on the Swiss Plateau as opposed to Berner Oberland or Upper Bernese, of the Alpine region) style of framing, the frame is indeed designed to avoid tension joinery whenever possible. There is of course the instance of the tying floor joists which must serve in tension -and these very strictly have no tenons. The tenon is unknown in tension joinery in this vernacular TIMBER FRAMING tradition, instead cogs, laps, and dovetail laps are used in these instances. It is worth noting that to this day lower Bernese framing has retained the let in, half lap dovetail joint for bracing that was discarded 500 years or so ago in most other regions.

As for the hung roof, my first post on this topic demonstrates that a hung roof can still rely on a heavy timber truss. The Liegender Binder of the Lower Bernese and general southwest Alemannic traditions is an example of this. This a heavy timber truss used to support hung rafters. I can show you, if I look through my photos I am sure I can find one, examples of a simple Stehender Binder from the same reason that looks remarkably like the picture shown by Louie. Just a few tweaks, notably eliminate the top cords as executed, replace them with struts from the post to tie. This of course necessitates the removal of the braces in this truss (or, more or less, flipping them over)

[Thehardway]

This is a great discussion.  Years ago, before the FF moved to the new format, we had a pretty thorough discussion of the King post truss and its variations.  I guess it could still be found in the archived section? 

Rooster brings up some valid points in regard to Jueston's rendering.  What Jueston has drawn is not really a king post truss although it shares some visual elements.  Likewise, the storefront pictures are not a true king post truss. 

A true king post truss supports the bottom chord (tie-beam) from sagging with the king post which literally dangles from the compression joint created at its apex by the rafters which wedge against it and grip it in a fashion similar to a ratchet.  The more weight placed on the rafters and king post, the tighter this joint becomes.  As long as the thrust of the rafters at the bottom can be controlled, this becomes a failproof design.  In some cases historically, rafter thrust was controlled by buttresses at the walls and a smaller tie beam could be used.  In later years, the tie beam bottom chord was in some cases replaced with an iron rod.   Hammerbeam "trusses" were not true trusses and could not have been used if buttressing walls had not been used to control the thrust at the bottoms.

What we see in the storefront and in Juestons drawing are actually ridge posts, not King posts.  They do not hang, acting in tension rather they support acting in compression.  The elusive factor in the storefront picture which makes it functional from an engineering standpoint are the knee braces. They diminish the unsupported span and increase the loading capability.  These are not true truss designs but rather ridge beam and rafter designs.  IMHO they are imposters of the king post truss.

In the diagram Jueston draws, I see what I would refer to as a Bridge Truss or Parallel Chord Truss.  It has a Ridge Post at the center on top of it.

In most historical structures, the Bridge Truss was used to span the length of the building rather than the width and supported at the ends by massive posts or masonry walls
Bridge trusses carried  at intervals, the weight of common rafters joined at the apex by a tongue and fork joint or a ridge board.

If I had to build a large span truss using 12X12 White pine, I would likely use the Queen post design as it can break the bottom span into three, well managed and well joined sections and better provide support at the rafters through triangulation.  I think 36' would be a reasonable target span with these sized members.

Similarly, the timber construction shown in the Swiss castles and homes I would not classify as a true truss.  What I see in the pictures seems to be a cross between a cruck frame and a modified scissor beam construction.  In some instances it almost resembles a modified hammerbeam style.  It is truly unique vernacular and the steep pitch is the structural key as it limits thrust allowing joints to work in compression rather than tension.  Very interesting pictures and good discussion.

I am toying with the idea of using Virginia Pine to build a few continuous top and bottom chord Bowstring trusses for a machine shed.  They are strong and easily bent and come in lengths exceeding 35'

[jueston]

yes when I made that model I didn't fully understand how a king post truss worked, after rooster commented on mine it was an aha moment for me, I really came to understand that the loadbearing element is the top part and that's holding the bottom piece, which is preventing the ends of the spreading, and the diagonal bracing helps prevent sagging and keeps everything from moving around too much.

[D L Bahler]

Just curious as to what you consider to be a 'true truss'

Not arguing with your assertion, just trying to understand how you are using the terminology.

I understand that in the timber framing world, the word 'truss' often tends to have a very specific meaning and application, referring usually to a complex roof framework supporting a purlin roof, for example.
However there are other examples of trusses even within the limited context of timber framing, such as the bridge-style trusses employed to support a floor or tying assembly over a span that needs to be left open, such as in the driving bay of some barns.

A truss, literally speaking, is any framework comprised of a number of members arranged in such a way as to distribute loads in such a way that cannot be done by simple posts and beams. Using this very open definition, the framework of the castles and farmhouses is certainly a truss system -the large roof framework distributes the loads of the very heavy roof of the castle, allowing for an open floorplan in the spaces below the attic level. The steepness, full hipped design, and sheer size of the castle Then roof alone requires a very complex framework. This is, technically speaking, a truss system.

However, in the terminology used among timber framers, this doesn't fit into the notion of a 'truss' as it is often meant. But this then raises the question, do you consider as trusses the framework of German cathedrals or Church spires? The framework of the massive Bern Cathedral is very similar to the framework of the castles in the Canton, many of the Castle roofs date to around the same time period (even if the castles themselves are much older -these roofs were replaced with Gothic Style frames near the close of the Middle Ages almost invariably). The roofs of Bernese castles and the framing of the Bern Cathedral roof are a part of the same tradition.

In German we use the term 'Dachstuhl' to refer to a roof framework. This can get confusing, because if you type this into a machine translator it will likely return 'roof truss' but that is inaccurate. The reason I say this is to demonstrate that in different building traditions, a term or collection of terms is used to a different emphasis. English roof framing focuses on trusses, for the most part, while Western Germanic framing emphasizes the purlin roof, very often directly supported. So we in the English speaking world in regards to timber framing have adopted the word 'truss' to apply to a specific set of frameworks or variations thereof, while in German, they take the equivalent tern and apply it to a totally different set of frameworks.

This is demonstrated by the fact that, in English, there is no simple term to describe a directly posted purlin roof, while a hammer-beam or king post can easily be classified as truss. In German, on the Contrary, the posts would be a 'Stehender Dachstuhl' and the hammer-beam or kings post design would be a little more awkward to describe -the languages have evolved to emphasize what is common.

This all gets confusing when switching constantly between languages. Most of my knowledge, for example, comes from German language resources, and very often I don't know how to describe to you something in English. I get terms confused because they don't overlap.