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Re: DachKontruktion - Roof Construction #25472 02/08/11 01:09 AM
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Hi D. L.

First some housekeeping:

I could not get the illustration on your January 20th post to enlarge, if this is true with others than the names are illegible.

In your sentence just under this illustration "It should be noted that terminology is note 100% compatible with the common English terms, especially when classifying joints." I think note should say not.

And, I do not understand the description pfettendach roof. I see lots of collars, what do you mean "...Stehender Pfettendachstuhl [directly posted purlins that support the rafters, no collar ties]"?

The Liegender Kehlbalkendachstuhl did make it to America, particularly in places Germans settled in numbers and is known by the simpler name "Liegender stuhl" such as is illustrated in the book The Pennsylvania barn: its origin, evolution, and distribution in North America. It may be a coincidence but this type of assembly is a relatively common way to frame a gambrel roof, too.

http://books.google.com/books?id=y6T_kOFmeRQC&pg=RA2-PA209&lpg=RA2-PA209&dq=%22liegender+stuhl%22&source=bl&ots=Lhc1WlKiUX&sig=imOmovgKXfCs3_QcDYMnJxEyuGk&hl=en&ei=npNQTdHbE9PpgQfc-rC-CA&sa=X&oi=book_result&ct=result&resnum=6&ved=0CEYQ6AEwBQ#v=onepage&q=%22liegender%20stuhl%22&f=false.


I find it interesting that the use of an upper and lower plate capturing a tie beam or joist is such a widespread European technique. I think it is an ancient form.

Also, is there much difference between the names of the framing pieces in standard German vs. Swiss-German? Other dialects?

Thanks;
Jim


The closer you look the more you see.
"Heavy timber framing is not a lost art" Fred Hodgson, 1909
Re: DachKontruktion - Roof Construction #25474 02/08/11 01:46 AM
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D L Bahler Offline OP
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Are you using firefox? With firefox right click on the image and hit 'view image' and it should load it full-size. I Don't know about Internet Explorer or Google Chrome or other browsers. If it is a problem, I can post links to the pictures.

yes, note should say not. Unfortunately I can't go back and change it any more!

In a Pftetendach roof there are collars many times, but if you look closely you will see the purlin is above, not below, the collars. In this case, the only function of the collars is to support an attic floor. The purlins here support the rafters, in a Kehlbalkendach the purlins support the collars.

In German, the Ligender Kehlbalkendachstuhl is usually just shortened to liegender stuhl, but the former is its 'technical', descriptive name. Although Liegender Stuhl is more general and at times refers to a pfettendach as well. Thanks for the link, I had been wanting to track this down to see if it had made it over here!

There are various theories as to where the Gambrel roof came from. Sometimes it is thought to be an American invention, however this cannot be the case. Many suspect it has its origins in Switzerland, as it is common in certain regions, particularly the cantons of Jura and Schwyz, for barn roofs to be framed like this. I have heard it said that Swiss Mennonites who came from Kanton Bern by way of the Jura brought this type of barn with it. The Pennsylvania barn is at times credited to the Swiss Mennonites and Amish of Pennsylvania, both of which have origins in Bern and the Jura.

The American log cabin, it can be noted, also comes from Switzerland ultimately. The English settlers of America didn't have them. At one point thousands of settlers from Switzerland arrived in the Appalachians, bringing with them their blockbau techniques. The American corner joints are rather simplified versions of the old Swiss ones, intended for strict function and ease, and adapted to local hardwoods.

As far as the captured joists, the Germans at least came it is their invention, and spread to the rest of Europe from the Holy Roman Empire. It is not ancient, the earliest examples known are from the 15th century. Before that German houses were framed quite a bit like we make timber frames in America today.

As far as terminolgy, the German language itself has to be discussed. Until very recently it was almost an imaginary language, with most literate people able to read and write it but few of them able to actually speak it. The German dialects are quite diverse.
Germany, and Switzerland have 2 different standards, but they are very similar. Sort of like American and British English. As far as I can tell, the terminology tends to be more or less the same. A large reason for this is likely that they are in most cases learned from books.

There are a few 'dialekt' terms I have come across no and then, but scholarly publication tend to use more or less the same terms.

One example, however, of how terminology can vary is the name of a post. It can be called a Pfost, Ständer, or Steil. These three can also at times have more distinct meanings, a Pfost for example may refer to a buried post, and Steil may be used to refer to a stud. The joists can be referred to as Balken or Deckenbalken (beams or ceiling beams) and the names of roof structures vary, mostly with how descriptive the writer is trying to be. (Liegender Stuhl v. Liegender Kehlbalkendachstuhl)


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Re: Southern Germanic Framing [Re: D L Bahler] #25496 02/10/11 02:53 AM
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D L Bahler Offline OP
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Some more things for consideration:

It is very common in German framework, and almost universal in Switzerland, for the braces to stretch from the sill to the plate, creating very long slanted braces. There is a very good reason behind this. These braces are resisting storm loads in buildings that are using relatively small posts for support, which are joined above and below with short tenons. By not having the braces brace into the posts, they are not required to handle any extra loading during storms or high winds, but rather the brace loading is transferred directly to the length of the horizontal timbers. This, however, has the disadvantage of not forming triangles.

Braces can be slanted inwards and join to wall posts, forming true triangles. The same problems still apply but are alleviated by having an opposing brace press against the other side of the same post. This requires a lot of wall space, and so is not always practical. The former setup has proven itself to be more than efficient, and is the dominant technique used in nearly all non-decorative Fachwerk buildings.

As for the small posts, there are two reasons why this is used:

1, as mentioned earlier it allows you to use smaller and lower grade materials without detrimental effects.
2. Apparently one of the primary factors in developing this system was to create interior walls that are free from intruding projections. IF the timbers are seen on the inside of a German house, they are flush with the wall surface.

In the case of barns and utility buildings this is not a concern. These buildings are very often built with more of a bent-profile style of construction, or at least a Fachwerk style wall with much larger timbers. It is rare, however, to see barns in the Canton of Bern. The common farm setup in most of the region is the large Bauernhause, which has a two level structure which serves on one end as the stables and on the other as the living quarters, and has a large upper level (the Heustock) that provides storage for hay and farm equipment. This upper level is accessed by a large framed and usually fully enclosed ramp.

What is interesting about the Bauernhaus is it appears to be descended from a Medieval predecessor that was typically built of stone. These stone houses were limited to the wealthier farmers, and the advancements in timber framing allowed this type of farm setup to be used by everybody.

One thing about posts, there are 3 categories that posts in the typical Fachwerk wall (Fachwerkwand) can be put in.
1 The Ecktänder, or corner post. These are generally the biggest posts. They must be made of adequate size and proportion to resist forces in two directions.
2: The Bundständer. These are posts where two walls come together. Very often they are somewhat wider than the the other posts to accommodate the thickness of the adjoining wall.
3: the regular old Ständer. These are the posts that aren't in the corners or aren't at the junction of two walls. They are typically rectangular in cross section, as they only need to be able to resist lateral forces in 1 direction. They mark the inner and outer surfaces of the wall, and they depth determines the dimensions of everything else as it is desirable in Fachwerk to have smooth inner and outer walls.

I also found this good picture, which does a good job of illustrating the setup and joinery of a simple wall. In particular pay attention to the different scarf joints used for the sills and the plates, reflecting the differences in the loads they are expected to bear. Also pay attention to the fact that the 'Riegel' around the bress is let in (verblattung) rather than mortised in.


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Re: Southern Germanic Framing #25525 02/14/11 10:08 PM
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Interesting.

I have been using internet explorer and now Google chrome which is much faster, at least on my six year old laptop.

I have researched the gambrel roof and here is the bottom line of what I know. The origin is not known but was used by Pierre Lescot on the Louvre in France around 1550. Often credited to Francios Mansart but not correct. Mansart did however popularize the style and thus France is the popular origin of the gambrel since about 1625. The earliest gambrels I have found in America were on mansions and truly architectural buildings like the second hall at Harvard College (built between 1672-1682, burned 1764) and the Peter Tufts house of 1675 in Medford, Massachusetts, possibly the oldest brick house in the USA. I have found about fourteen ways to design a gambrel roof in historic carpentry texts, mostly in French books and some German.

Jim


The closer you look the more you see.
"Heavy timber framing is not a lost art" Fred Hodgson, 1909
Re: Southern Germanic Framing #25526 02/14/11 10:32 PM
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D L Bahler Offline OP
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Look for old buildings in the Jura, the East Midlands and central Switzerland (All in Switzerland). Those are the regions where I am aware of the popular use of Gambrel roofs. The Jura is mostly French speaking, and so it is entirely believable that it could have entered there by way of France, however the other two regions have virtually no French influence, and are historically isolated from the French Cantons by the large Canton of Bern and of course lots of mountains and valleys. I would be very surprised if it was a French technique in that case. I have always understood and assumed that it developed naturally out of the dominant Liegender Stuhl roof system that is the most common roof in timber frames in German Switzerland by far. It seems to be a common roof (the gambrel) in all of German Switzerland except in Canton Bern which has its won very unique architectural style.


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Re: Southern Germanic Framing [Re: D L Bahler] #25654 02/25/11 06:48 AM
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Check this guy out
http://www.swisswoodenhomes.com/en/home.html

This guy is one amazing craftsman
Look at the pictures of his work, and be awed

The amazing thing is, nearly all f the old houses where he is from (Judging by building style and decoration style, I would guess the Berner Oberland region) are at least as richly decorated as what he has shown here, sometimes a LOT more


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Re: Southern Germanic Framing #25673 02/25/11 08:23 PM
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D L Bahler Offline OP
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A little bit about bracing...

It has come to my attention that I should deal with the matter of rigidity of frameworks. The American frame is a very flexible assembly. It can move a great deal without any danger to the structure. Unfortunately modern codes require us to stiffen our frames somehow when we build them.

The Germans, on the other hand, build frames to be immovably rigid. They are built so that they just will not be swayed.

This simple fact is very likely a big reason for the drastic difference between the bracing techniques in American and German framing. Knee braces are all but unheard of in later German framing, instead they rely on very long braces. This is because they are expecting their braces to do two things, resist racking and resist lateral force. A short knee brace does an excellent job of resisting racking, but a terrible job of resisting lateral forces.

Since they are expected to bear 2 forces simultaneously these braces must be treated a lot differently. They have the potential to have a lot more force transferred through them than a knee brace typically will have, and for this reason it is considered bad practice to brace them against a post without an opposing brace on the same post (never on a corner post) The forces during a storm could potentially push the post out of its joint.

The reigeln also help a great deal in this regard. They by themselves don't do anything to prevent racking of the frame -dividing a rectangle into two rectangles doesn't make it any less likely to change its angles- but they do greatly limit the flexibility of the frame. The assembly makes it so that all of the posts are pushing against each other, almost eliminating the possibility of any timbers flexing under lateral loads.

When you add to this the long braces which cross the reigeln and bring them into bracing action, the frame has very little ability to rack or flex much at all.

The is 1 potential weakness with the German frame. A very long wall with no supports in this system is unstable, and the building has the potential to flex in the middle which is certainly not good, particularly with a masonry infill.

There are 2 commonly used solutions to this. The first is to brace the walls against each other and against flexing with an interior wall built in the same fashion as the exterior walls, perhaps a little thinner. The second is to use a series of framed buttresses, usually on the inside. Essentially these are wall frames about the length of 1 or 2 cavities, complete with braces and riegeln. The first is the most common, and can be easily incorporated into the floor plan of the building. The second is used if there are no walls close to where bracing is needed, such as in a large hall.


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Re: Southern Germanic Framing #25876 03/13/11 06:55 PM
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Hi D. L.;

If you ever see a building with a gambrel roof that is thought to be from before 1625 I sure would like to know about it.

The above illustration is titled "Bundständer". What does bund mean and are you familiar with the highly decorative type of framing known as bundwerk?

I just found a copy of the book Schweizer Bauernkunst by Daniel Baud-Bovy (1926) at a local antiques store. Now all I need to do is figure out the darn text and learn to read German! Nice illustrations and photos.

Thanks;
Jim


The closer you look the more you see.
"Heavy timber framing is not a lost art" Fred Hodgson, 1909
Re: Southern Germanic Framing #25877 03/13/11 09:26 PM
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D L Bahler Offline OP
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Hmm, can't say I'm not more than a bit envious of your acquisition, Jim. How long is the book? If it is not too long, is there any way you could make digital images of the whole, including the text, and send them my way? If you could do this, I am sure I could in exchange help you translate from the German, depending on how technical the text is.

A Bundstaender is a post that joins 2 walls together, and as such is generally a bit larger than the other wall posts. 'Bund' here having a meaning similar to the English bond, with which I am sure it is a cognate. From what I can tell, bundwerk is a kind of cross timbering, or timbers crossing at diagonals to from a repeating X pattern. Common on some gable walls, where it is easier to execute in some instances than a regular frame.

from the German Wikipedia, bundwerk



Last edited by D L Bahler; 03/13/11 09:28 PM.

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Re: Southern Germanic Framing #25934 03/18/11 06:02 AM
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in the way of an update of sorts...

I have been learning about 'Riegelbau' from a Swiss carpenter. Riegelbau is the Swiss version of the German Fachwerk, which can be done either in Gefäch, or half timbering, or covered over with siding. Regardless of the enclosure method, the framing is basically the same. The interior of such structures is almost always covered over with wood panelling of some sort, or in later examples plaster, the timbers typically are not exposed and the framing techniques go to great lenghths to ensure an even interior surface to serve as a basis for a smooth wall, meaning things like corner posts are specially shaped so as not to intrude into the interior space.

regarding the Swiss Reigelbau, here is some specific information:
Posts are typically somewhere around 5x5", maybe 4x6 or ssomewhere in that general area. The posts are spaced at intervals of about a 3 to 4 feet apart.

Sills come into 3 different categories, there are the ground sills, the wall sills for upper levels, and sills that support the rafters or roof framing in general. These are all perhaps 6x8, the extra width compared to the posts would stick to the inside.

The ground sill corners can be joined with a pinned though mortise, or in more modern building may be joined with a hidden lap joint reinforced with steel bands bolted on the outside.

The Swiss do often use the typical German method for constructing floors, where the joists are captured between plate and sill, but there is another method that they sometimes use as well.
In this case, the joists are maybe 6x6, and are dropped into the sill beams to sit flush with the top, reduced to 3 inches thickness whre they pass through the sill. The joint here is complicated, and I will have to put up a picture. It is important to note, the joists typically pass through the sill and stick to the outside of the structure a good ways, where they may have ornately carved ends or simpler adornments, or may stick out even further to support balconies. joists are spaceed 2 to 3 feet apart.

The posts are joined to sill below and plate above by means of very short tenons, which are around 1 1/2 to 2" in length, and are not pegged. the long slanting braces are joined in the same way.

the horizontal 'riegeln' are perhaps 4x5", and these may be pegged in place, but very often aren't.

There are 2 special categories of posts, the corner post and the 'Bundständer'. The corner post is often quite large, maybe 8x8 to perhaps 10x10 or even larger. However, the inside corner is cut out to form an 'L' shaped timber whose inside faces will sit in the same plane as the inside faces of the other 5x5 posts to form a continuous wall plane. The bundstaender stands where an interior wall joins the otside wall, and as such is made larger, perhaps 6x8. Once again, it is shaped with cutouts to create an even wall plane, giving it a shape somewhat like a squatted 'T'

There are a few special joints that too must be adressed,
first, in the swiss method where the joists sit flush with the sills, rather than being captured between sill and plate, there are 2 special joints needed. The timber that sits on the end walls, which in the German method would joined as another joist, must in this case employ another type of joint. This timber is made the same size as the top plate, 6x8, and in fact is both a top plate for the lower end wall and a sill for the upper.

This timber sticks out past the side wall a good ways, and the plates for the side walls are joined into it with a joint called a 'Schwalbenschwanz" which in English would be called a dovetail (the German word means Swallowtail)

The sill for the upper level therfore sits directly atop the plate, and is joined to it with pegs. in the other method where the joists are captured, the sill is instead joined with the 'kamm' joint and also pegged to the joists.

The other special case is the instance of a ridge beam, which is not always used. Here there are 2 ways in which it might support the rafters. The old way is to have the top of the beam peaked, with the rafters simply resting on top, joined to each other with a bridle joint. the newer way is to have a flat top, with bridmouths in th rafters to sit on top of it, and secured in place with a long spike or screw. here the rafter pairs would just be cut flush to each other and nailed together, the idea being that the weight in the old system is born by the bridle joint, whereas in the newr system it is born by the birdsmouts in the rafters.

the rafters themselves would be about 4x6, at the same spacing as the joists, purlins would be about 6x10, with their supporting posts 6x6 and braces 5x5

in the Bernese style, a gable overhang might be about 4 or 5 feet, while the eaves might be 3-7 feet, or even more on larger buildings with wide balconies.

a typical roof pitch is about 40 degrees, which more or less corresponds to a 10/12 pitch which is 39.81 degrees

thats enough for now, feel free to ask any questions


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