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#25276 - 01/22/11 11:53 AM Re: Infill and Half Timbering *
D L Bahler Offline

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Registered: 05/17/10
Posts: 946
Loc: Indiana
Gabel,

When dealing with a half timbering system, I am naturally assuming that one will be copying some old world European style of building such as those pictured in a previous post. In this case the boards will have to interface with very long braces, and are going to have to be keyed into them. It does appear however that in the European Bohlenwand the planks are not keyed into any horizontal members, and the top faces of horizontal members, or at least the ground sills, are sloped outward to let water drain off.

I like the idea of the borads forming a 'floating panel' between the posts. They would be free to slide back and forth and so would not be compromised in any way by post movement.

On the subject of the foam anti-draft layer of spray foam:
I have thought about this, and decided that any sprayed or plastered on substance that is intended to resist draft is going to crack and break as the wood moves seasonally. What I am now considering instead is using housewrap on the inside of the cavity instead. It would stapled up against the outer plank layer, against the sides of the posts, and could wrap around into the rabbets for the from planks to ensure no draft gets through. Or, alternately, foam could be sprayed along the edge of the wrap on the post to do the same. The housewrap would be able to move freely with seasonal changes in the wood without loosing its seal, and it doesn't seem quite as risky concerning moisture issues as the foam.

Gabel you also mentioned about building regulations, that of course is the big question isn't it. What problems do you foresee that should be addressed?

The diagram I made uses 7" deep walls, leaving a 3-1/4" cavity for insulation. 3" of extruded polystyrene foam board would be about R-15, compared to a fiberglass which for 2x4 is r-13 and 2x6 is r-19. There is less thermal bridging in this than is a stud wall, and when you factor in the insulation and thermal mass properties of the planks and clay you will probably still come to an average of about r-15. I haven't done any real calculations, that's just a rough guess. This system would perform at least as good as a standard 2x6 stud wall, and of course making the posts deeper would push the r-value up even more.

I will do some figuring and put up an r-value comparison later
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#25277 - 01/22/11 12:29 PM Re: Infill and Half Timbering
D L Bahler Offline

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Registered: 05/17/10
Posts: 946
Loc: Indiana
The Figures are in:

The cavities have a total r-value of around r-18, actually slightly higher because I did not figure the value of the clay and plaster, and rounded down. This is the combined r-value of the foam board, 3/4" outer planking, and 1-1/2" inner planking

7" thick posts have an r-value of about r-8, slightly more for most softwoods, slightly less for hardwood.

I figured that the cavity generally occupies about 88% of the surface area of the wall, and the frame about 12%. For more complicated framing the frame may occupy as much as 20% of the wall area. 20% frame gives an average r-value of 15.5, 12% frame gives an r-value of 16.5. This is every bit as good as a 2x6 wall with no exterior foam insulation.

here is the formula I used:

a= average r-value
f= r-value of the frame
c= r-value of the cavity
The wall is divided into 20 sections, with each portion given its proportion of the 20, so the frame has 5/20ths of the wall area if it is 20% and the cavity would be 15/20ths

a=(5f+15c)/20, a=(5x8+15x18)/20, a=15.5
or
a=(3f+17c)/20, a=(3x8+17x18)/20, a=16.5

Not a super home by any means, but nonetheless a more than adequate insulator. Certainly meeting the prevailing standards.


Edited by D L Bahler (01/22/11 12:32 PM)
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#25278 - 01/22/11 06:26 PM Re: Infill and Half Timbering
dbailly Offline
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Registered: 02/18/09
Posts: 8
Loc: Berkshire County MA
DL,

I just wanted to through my two cents into the mix. First there is a timberframer here in Western MA who lives around the corner from me who is currently building a Half-Timbered shop. He has used tradition brick infil and it appears that the timbers have been treated with something. (Not to through Dave Shephard under the bus, but he might know a few more details as he helped raise the frame.) You mentioned that you were concerned about your effect of the local climate on the infil, well we are already over 5 ft of snow, we've had freezing rain and temps reaching 15 below zero. Plus July and August are filled with 95 plus degrees and 95% humity days. Of course no matter what you do you will have some maintenance, so I would say go with your heart. As for the interior finish and insulation why not combine the brick infill with the slotted board system. This would also leave an air space for the insulation of your choise. Good luck. Be sure to post pics when complete.

Dan

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#25279 - 01/22/11 10:18 PM Re: Infill and Half Timbering
TIMBEAL Offline
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Registered: 12/10/07
Posts: 1872
Loc: Maine
Out of curiosity, when we pour large concrete slabs there are control joint cut into the surface to control where the crack goes, this is due to the high rate of shrinkage. So I wonder if you were to apply the same theory to a daub wall and force the cracks to happen in specific places one could go back and fill these cracks later after it has dried. Otherwise it just shrinks willy nilly.

If my understanding is correct, bricks are small enough and independent of one another, as such, they do not shrink on a large scale. Similar to 2-1/2" wide hard wood flooring compared to wide boarding.

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#25280 - 01/23/11 12:18 AM Re: Infill and Half Timbering
D L Bahler Offline

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Registered: 05/17/10
Posts: 946
Loc: Indiana
Tim, That's a thought. But even still the nature of Daub is high maintenance. The difficulty lies not only in the fact that it shrinks as it dries, but that the formation of frost within causes the molecular structure to break down over time -the same affect that you use to your advantage when making any loam wall material as you leave the dirt to sit out in small piles over the winter so that the frost can break it down.

To alleviate this problem, clay bricks rely on the addition of sand and other aggregates. And many times the Loam wall systems are mostly straw and have very little actual clay in them. (This is not only true of the modern Lehmbau, but also of older techniques dating back to the middle ages)

About the issue of bracing on the bohlenwand:
The Bohlenwand is a major part of the Swiss tradition. In Switzerland the general practice is to have the planks sit flush with the inside of the wall, and the braces are then let in from the outside. These braces rely on lap dovetail joints. Alternately the planks are set in the middle, and thin braces are let in on both the inside and outside.

Example:


That image is from a very good book, the part covering Bohlenwand can be found here:
http://durm.semanticsoftware.info/wiki/index.php/Durm:Bohlenw%C3%A4nde

Browse through that book, It's incredible. Great pictures that show a lot.

Obviously let in braces will not work if the board are 3/4 of an inch from the edges of the timbers.

A possible solution, however, is to instead nail boards onto notches cut on the outside of the timbers (the timbers would have a cross section somewhat like a fat +) This would actually solve 3 problems at once, it makes it so that inserting the boards around braces and such is quite quick and easy, it makes it so that the boards can be inserted after the frame is raised, and it eliminates the problem of the floating boards moving relative to the top plate, which could cause serious plaster issues.
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#25281 - 01/23/11 06:48 AM Re: Infill and Half Timbering
TIMBEAL Offline
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Registered: 12/10/07
Posts: 1872
Loc: Maine
I would wonder what percentage of moisture it takes to saturated a clay/straw wall enough to cause freezing and thawing, in effect crumbling the wall. The walls are to be constructed in the dry season allowing enough time for them to dry before cold temps set in. I see a dry wall with protection very different than a pile of clay exposed and fully saturated with water.

I keep reading clay and loam being used interchangeably, just to clarify, I don't feel comfortable using loam. For some unknown reason, I can't put my fingers on, clay seems to be the better choice. So when I say clay I mean clay not loam.

Most systems require maintenance, it all depends on what level you feel comfortable maintaining the system.

At Fox Maple, Steve Chappell's place, I noticed they were using kerfs cut into the sides of the timber for the infill to key into, so when the shrinkage occurs there is some sort of blockage to keep old man winter a bay. These kerfs acting similar to the planks inserted as the frame goes up. I am sure that system is not perfect either.

Speaking of foam built into a infill wall system, as you point out frost building up within a wall could deteriorate the infill system leading to problems, as well. If the foam is not of sufficient insulating value, and there is moisture within the house trying to get out and moving into the wall system, it will hit the blockage of 1-1/2" foam board and build up. If the outside temps are sufficient enough to to freeze the moisture on the inside face of the foam, I see this as an issue to consider. This is just one of many scenarios. The point which I think has already been made, adding modern components to older technologies may have hidden consequences.

It is all ways fun to reinvent the wheel or at least attempt. If nothing else is reassures the old method still works the same as it always has, even with its, known, pit falls.

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#25283 - 01/23/11 12:03 PM Re: Infill and Half Timbering
Cecile en Don Wa Offline
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Registered: 08/08/09
Posts: 259
Loc: the Netherlands
Hello,
From what I read here, traditional infills are not normal in the work of timber framers writing regularly on this forum. That is interesting in and of itself.
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#25284 - 01/23/11 02:07 PM Re: Infill and Half Timbering
D L Bahler Offline

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Registered: 05/17/10
Posts: 946
Loc: Indiana
I would guess that 15% moisture content would be enough to cause trouble. In Indiana, things generally will settle at a moisture content at around 12 to 15% or so because humidity levels remain very high all year. If exposed to the hot and the cold I foresee issues.

Where it is normally employed these problems don't exist. In my travels I have realized just how harsh the weather in my home state is. Central Europe seems like a paradise when compared to the Midwestern US.

In Fachwerk, the infilling tradition I am familiar with, the bricks are keyed into channels in the post. Also the frame is designed for infilling, the posts not being any larger that 4 or 5 inches wide will not shrink much and so won't cause large gaps.

About reinventing the wheel, well it should be noted that the wheel has been reinvented many times over the past several thousand years. It has been advanced and made better. A few notable examples being the invention of the spoked wheel, and the pneumatic tire, and the wheel bearing.

In other words, there is absolutely no reason why we can't improve on old ideas. We need to adapt them to modern conditions, or else just watch them fade away entirely. The Swiss probably wouldn't use the Bohlenwand at all today if someone hadn't figured out a while back how to insulate it.

Now we can't do that haphazardly. Our innovations need to be well thought out and carefully managed. That's why we talk about them here, and I certainly value your input. But I just wanted to step up and say, there's nothing wrong with wanting an infill system that also performs well by modern standards of living. If you want people to actually spend their money on them, then that is a necessity.

Of course there are a few issues that need to be worked out, after all I just thought of the idea two days ago.

As for the boards moving up in down in the channels and causing plaster problems, I thought of a simple solution to that. After they are in place where they need to be, secure them with a single nail on either end. That way they can still expand and contract without creating a huge gap at the top of the wall or destroying the plaster or cracking. If supporting plaster these boards should probably be no bigger than 1x6, with 1x4 probably best (any smaller would be too wobbly). For the inside where the wood is exposed, the Swiss solved that problem. A trim board is attached at the top to the frame but not to the planks, hiding any gap that may form.

Don, I know what you mean. Traditional infills haven't seen much exposure in the US. Although many people I have shown pictures to have expressed some interest in the concept -the visual affect cannot be matched.


But back to the topic of my Shop.

My current plan, I think, is to go with a traditional Bohlenwand technique.
Part of the intention of my design is to replicate the style of building that is to be found where my Family comes from, Wattenwil Switzerland. So with that in mind I am considering doing a Bohlenwand with exterior let in braces, complete with richly carved timbers inside and out.
But I am tempted to try out my concept to see how well it actually works. Decisions decisions...

I like the way the all wood houses are decorated. That's a major plus for me. The major disadvantage of course as that a purely traditional infill has just about no insulation value whatsoever. But by using lots of big wood on interior walls the houses built this way are still quite cozy in the winter. The Kachelofen I think helps too.
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#25294 - 01/24/11 12:11 AM Re: Infill and Half Timbering
D L Bahler Offline

Member

Registered: 05/17/10
Posts: 946
Loc: Indiana
something should be said of the way European infilled structures are designed. THere are, I see, 2 major classifications that might be used.

The first is the use of a frame designed specifically for the purpose. This would be like the German Fachwerkwand, where the entire framing system is originally designed around the use of brick and stone infills.

The other is the use of an all purpose frame modified to support infill. Basically this would be a studded timber frame where the weight of the structure is born by a few large timbers with small studs between them. This seems to be the prevailing style of England and France.

Which style is better? Well who is to judge> Both have proven themselves. The Germans claim that the true half-timbered frame originated with them and spread to the rest of Europe, this meaning the frame designed to support brick and stone instead of wattle and daub which is generally considered to e inferior by the Germans.

It is also important to note 1 thing about the infill. The Germans say that you should never expect the brick, stone, or whatever to have any structural properties whatsoever. You should not expect the infill to bear any of the roof load, or stiffen the frame, etc. even if it is made of high quality brick or well crafted masonry.

I have to ask about wattle and daub. If you have a frame system clearly designed to support an infill why bother with it?

The advantage of wattle and daub is that it can be made to cover as big an area as needed. You can build a house with a few posts and then set a series of stakes to build your wattle on, and so forth. Such is how early medieval houses were built.

But in Germany the half timbered structure was invented to get rid of the wattle, and use better materials instead such as brick, fired or unfired, and stone or even wood. I can't say for the development in other countries, as Germany is what I have studied, but I imagine the reason is similar.

So what would be the advantage of using wattle and daub? The Germans in the later middle ages occasionally used it to fill interior walls because it is obviously cheaper than nice bricks, but never trusted it on the outside.

The big advantage of bricks is that once they are there, they are there. They have been made in such a way that they are not going anywhere, especially if they are fired bricks.

The Germans have the following wisdom to offer on earthen wall materials:
The best material to use is a mixture of clay, silt, and sand. Too much sand makes it too lean and it crumbles, too much clay makes it too fat and causes it to crack and break apart. Straw is added and is not expected to serve as aggregate, but to alter the density. The addition of manure makes it stronger because of the mineral composition, also horse manure works the best as it has undigested cellulose fibers in abundance. Lime added to the mixture neutralizes acids in the mischt and produces preservative salts.

With all this, though, the general consensus among most Germans seems to be that brick is the best suited material for infill, and after that is stone. The infill is usually covered up with plaster at least on the outside, and often on the inside as well. The biggest reason would be that by so doing you can use cheap bricks, such as those from the outside of the old style kilns that aren't fired as well and have black all over them. The lime plaster covering protects the cheap bricks which would otherwise deteriorate quickly, and also hides their ugliness. In modern usage, this means you could go to a brickyard and buy their left-over bricks, bricks that were sent back as extras from orders. They are generally quite a bit cheaper and mismatched. but that doesn't matter if you are covering them up!

In France, it seems that in many cases instead of plaster gypsum is used. There is, after all, a reason why gypsum plaster is called plaster of Paris, as it used to come from mines in France.
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#25299 - 01/24/11 09:20 AM Re: Infill and Half Timbering
bmike Offline
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Registered: 01/09/08
Posts: 918
Loc: Burlington, VT
I'm still wondering what wood you'd see as optimal for this. Shrinkage and checking, as well as potential rot, water damage, and vapor drive would be issues to me... especially in a modern residence with lots of potential moisture coming from inside the house, and dramatic swings in temperature.
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