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#33465 - 02/13/16 01:15 PM Double-Wall Enclosure Concept
TCB Offline
Member

Registered: 02/10/16
Posts: 26
Loc: Texas Hill Country
I'd first like to introduce myself and thank the good folks here for hosting this wealth of information, and making it freely available to everyone. I've been frantically reading through as many threads with a low enough jargon-density for me to understand what is going on; I've no formal training whatsoever in framing, but the design philosophy and craftsmanship really appeal to me as an aerospace engineer and amateur machinist. The plan is to learn as much as I can over the next several years as I narrow down the design & build up a war-chest, and by then hopefully have a good idea of what all I will be doing myself vs. hiring specialists/contractors for.

That out of the way, I'd like to pick ya'll's brains about an enclosure/framing concept that seems like it might have some merit. I've been trying to learn about enclosure methods, and just haven't been able to get excited about the daub-styles which seem to require a lot of maintenance & are somewhat limited as far as their design flexibility. Stick-built infill walls w/ plywood or SIPs just feel like cheating. So I looked into wood joinery-based systems, and found this diagram on a TFG thread;

Seemed very simple and straightforward, and seems to have served rather inclimate parts of Europe well enough. But it is ultimately a single layer of wood, to which daub or secondary paneling must be applied in order to get any degree of insulation or draft-seal (not to mention routing paths for conduit in a modern application)

So I wanted to see if there may be a way to adapt it to a double-wall layout;
-Similar to the Swiss style shown above that uses T&G slats stacked horizontally & set into vertical frame grooves to make a wall (Bohlenwand?)
-Instead of trying to use a super-thick timber to put two sets of grooves in to form an insulated cavity, use two parallel (smaller) timbers separated by an air-gap of several inches.
-The inner post carries the inner rafters of a double roof & the upper floor joists; the outer (taller) post carries the exterior rafters
-Columns are tied to eachother with several M&T cross ties along their length, so they function as a single load-bearing member as far as superstructure

Advantages;
-Seems to have all the benefits of a standard 'wall truss' arrangement, but without any thin spot in the insulation at the rafter/wall transition
-Wall can be made arbitrarily thick with about the same qty of timber
-Greatly reduced thermal bridging through the frames by way of conduction; a concern brought up for a super-thick post version
-The cross ties connecting the posts could be made to form a 'tunnel' for vertical wire/plumbing runs
-In my concept, the interior wall is horizontal slats from the ceiling down to about 3ft, where it changes to a system of vertical slats (think wainscotting) that cover horizontal wire/plumbing/ducting routes & can be easily removed/replaced. Above the transition, things are sealed enough that loose insulation can be used, but the actual accessible area uses foam blocks more resilient to infrequent tampering
-Allows for a thick double wall of excellent insulation value, while allowing for exposed timbers on both sides
-Will allow for wall/frame relative movement without loading up the wall boards
-Eliminates the need for plaster or paneling on both sides; can be simple exposed wood slats if desired & designed properly
-I would think is very draft-proof due to the pair of tortuous paths to get past the frames or between the slats
-Potentially the exterior panels could be easily removable/replaceable

Disadvantages;
-Since it relies on two sets of posts, the foundation footing needs to be wide enough to support both (& they'd both need to be tied to the slab/etc.)
-Not sure how the sill would be addressed to keep water from pooling there should water make it to the exterior wall
-High lower limit to how thin the wall buildup can be
-Windows/door frames may need to be an essentially standalone structure coming off the floor plate, since the inner/outer wall can probably shift relative to each other unacceptably. Not sure how different this is than standard practice, though.
-Cost, complexity, etc. which would be a little bit worse than 2X the single wall concept. The smaller timbers could help here, though
-I assume the frame spacing has to be closer than otherwise required for mere strength reasons, so the thin slat panels cannot warp enough to form significant gaps. Intermediate studs may still be required to stabilize the slats against bending/warping, but may allow the slats to get much thinner than the thick slabs traditionally used

I do not currently have a sketch in digital form, but I can scratch one up if my explanation is unclear. Thanks again for your thoughts

TCB

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#33468 - 02/13/16 08:25 PM Re: Double-Wall Enclosure Concept [Re: TCB]
Hylandwoodcraft Offline
Member

Registered: 03/23/11
Posts: 141
Loc: Western NY
Hi TCB,
I'm sure you will find a lot of valuable knowledge on the forum, I know I have had a lot of food for thought!

As far as your question goes, it occurs to me that what you are proposing sounds a lot like a sort of timber framed Larsen truss. It seems like it would be much simpler to apply wall and roof trusses to your timber frame. It seems like the system that you are proposing would exponentially increase the time and complexity of timber framing a given building.

Are you sure that a plastered enclosure would be hard to upkeep in your area? I'm not sure on the area of Texas, but if it is the right climate it might be worth another look.

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#33470 - 02/13/16 10:57 PM Re: Double-Wall Enclosure Concept [Re: TCB]
Jay White Cloud Offline
Member

Registered: 11/06/08
Posts: 480
Loc: Vermont
Hi TCB,

I will do my best to run down your query and thoughts...

Quote:
...just haven't been able to get excited about the daub-styles which seem to require a lot of maintenance & are somewhat limited as far as their design flexibility...


Of all the infill methods (and there are hundreds if all timber framing cultures are taken into consideration) most are much more durable and insulative than many "think" or assume to be true. These still are a dominant form of enclosing timber frames and are still reasonably common in Europe and elsewhere as an efficient way to enclose and insulate a frame. More suited for less harsh climates of the temperate zones, they can still work in the colder regions as well with proper design...

Quote:
...So I looked into wood joinery-based systems, and found this diagram on a TFG thread...


The modality in the attached sketch/model is a common one in several cultures. Here in North America (there are...or where some examples in Louisiana) which are called "Piece sur Piece" and The other similar method is a "vertical planking system" often call Plank Frame Architecture ...Both represent a combination of timber framing and log or slab architecture...Depending on how and who facilitates this historical design, they can end up with a very functional and efficient structure...In some applications a "rendering" (aka plastering) may be necessary, yet in others and "all wood" system can be had as well...


Quote:
So I wanted to see if there may be a way to adapt it to a double-wall layout


There is...and probably too many to even begin to list... crazy Some better than others some more traditional than others..

"Wall Truss" systems (as Sean has referenced) are another (but different) modality. This is the system I recommend above all others for most Timber Frames unless following a specific "historic format" for a given reason or desire.

The commented advantages are many, such as the mechanical and wiring chases (aka "tunnels"), extra thick wall for little to no added cost, non bridging insulative modalities, deep window seating areas, improved storage capacity, et.

When I got to the disadvantages as described, I realised that you may be trying to create a "double walled" timber frame, which also exists, but is not as efficient in material utilization typically as a simple timber frame with a "wall truss" system. Since I tend to build almost exclusively on traditional stone foundations I can share also that a slab is not a necessity, even when using a double walled timber frame method, as even a stone plinth/socle system would support such a structures as would a simple "Raised Earth Foundation."

Hope that was of some assistance...

Regards,

j


Edited by Jay White Cloud (02/13/16 11:00 PM)
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#33473 - 02/14/16 11:13 AM Re: Double-Wall Enclosure Concept [Re: TCB]
TCB Offline
Member

Registered: 02/10/16
Posts: 26
Loc: Texas Hill Country
Hylandwoodcraft;
"As far as your question goes, it occurs to me that what you are proposing sounds a lot like a sort of timber framed Larsen truss. It seems like the system that you are proposing would exponentially increase the time and complexity of timber framing a given building. "
I actually got the idea for the frame-side of the concept by examining Larsen/Wall Truss builds. It seemed like they use an awful lot of vertical timber, though, almost approaching a sort of 'stick-construction' before sheathing is applied. My thought here was for the sheathing to be strong enough (and secure enough through joinery) that fewer vertical members would be needed to support it from the rear, while retaining most of the Wall Truss advantages. Think of a wall truss with several-foot gaps between the securing studs instead of 18" centers. Almost like building up a SIP between the main posts by constituent layers. The key to the framing portion is ensuring the two posts work together as a unit (which may prove trickier than I hope)

As far as complexity, it's a non-issue on this design for the time being (it's admittedly a bit of a science experiment I have several years to figure out, before deciding if it's worth it or not to preserve certain design elements). I'm also hoping the octagonal floorplan will allow for eight largely-identical "wall bents" to be fabbed up prior to raising, which would allow for a bit more subassembly complexity without being so annoying. The way it works (in my head) is that an assembled frame bent would have a second set of posts stacked onto the first before being raised. If the planks can be flexible enough to be bowed into place after raising, construction could potentially be very easy.

Jay White cloud;
"Of all the infill methods (and there are hundreds if all timber framing cultures are taken into consideration) most are much more durable and insulative than many "think" or assume to be true. These still are a dominant form of enclosing timber frames and are still reasonably common in Europe and elsewhere as an efficient way to enclose and insulate a frame. More suited for less harsh climates of the temperate zones, they can still work in the colder regions as well with proper design.."
I am certain Adobe can probably work out here with a generous overhang, and may even be quite viable to make with the limey caliche soil (basically crushed/compacted coral), but it simply isn't seen, nor was it historically common from what I can tell. Go much further west where it is much drier and it's common, though. Not sure if it's the high humidity swings (20-100), or the high temperature swings (0-120), or the character of the soil, but my worry is anything just moves around too much to avoid cracking & frequent repair. Heck, the worst part of the drought was wrecking full-on slab foundations, soil cracks being plumbed at over 10ft deep in more clay-ey areas!

Mostly though, I simply have no experience with it at all, and am uncomfortable embracing something so different from what I expect a 'wall' to look/work like. Historically, folks primarily had wood to work with (think Old Timey Hollywood western town construction), and before that frequently used cut/natural stone & mortar when they needed something more durable. Natives seemed to prefer caves, when available, or portable structures so they could follow the water. Lot of brick and limestone block, once railroads brought these products out, even to this day*.

"The modality in the attached sketch/model is a common one in several cultures."
That should mean it's as good an idea as pita bread & tortillas then, right? smile

"In some applications a "rendering" (aka plastering) may be necessary, yet in others and "all wood" system can be had as well..."
I figured plastering was feasible if that finish was desired; this plank scheme is somewhat like Wattle & Daub on steroids, after all. Not even drywall survives the weather swings more than a year out here without diligent climate control and high quality construction (peeling tape & warping is common in garage interiors), so plaster has its work cut out for it, even if it is slightly more flexible.

"There is...and probably too many to even begin to list... crazy Some better than others some more traditional than others.."
Interesting. Like I said, the forum I was reading through was trying to find ways to effect a double wall post/plank system, and it seemed like there wasn't much to draw from that they could find. Glad to hear it isn't such a wild idea, after all.

"When I got to the disadvantages as described, I realised that you may be trying to create a "double walled" timber frame, which also exists, but is not as efficient in material utilization typically as a simple timber frame with a "wall truss" system"
Yup, pretty much a double frame supporting a double-roof; but a stripped down one using slightly smaller timbers & wide-spaced intermediate posts. My goal is to see if the planks+support posts can rival or exceed the timber efficiency of a wall truss by halving (or more) the frequency of vertical elements supporting the infill. Admittedly, the whole purpose for the double frames was to create an airgap for better insulation, as opposed to simply making the posts thick enough for two parallel plank slots (or covering them up on one side with a wall truss)

"Since I tend to build almost exclusively on traditional stone foundations I can share also that a slab is not a necessity, even when using a double walled timber frame method"
Hill Country caliche isn't quite as bad as Blackland Prairie soil, but I think ground moisture (cycling from bone-dry to saturated several times a year) hydraulically moving things is why pier-based foundations have fallen from favor. Older pier structures have almost universal foundation problems (lots of foundation repair companies all over). They can certainly be done as the bedrock is usually less than 10ft down (or like 5ft in the Hill Country) but require more work drilling through rocky or gummy soil. Whenever someone gets a pool installed, the contractor has to bring in a massive 'rock chain saw' trencher to get anywhere!

Part of the issue is my present desire is to build into a hillside, which (needlessly) complicates things a bit, in ways our ancestors wouldn't have bothered with, but which I'd still like to explore as an option.

*Pretty much all the high-cost educational or government buildings getting designed by architects are using what I affectionately call "Jet-Stones" aesthetics; lots of limestone, lots of glass/aluminum, and arranged into rather futurist angular forms. Sort of a combination of the Flintstones and the Jetsons.
New Construction at A&M

TCB

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#33475 - 02/14/16 11:38 AM Re: Double-Wall Enclosure Concept [Re: TCB]
TCB Offline
Member

Registered: 02/10/16
Posts: 26
Loc: Texas Hill Country
Hopefully this helps, somewhat. Planks set into grooves in the two sets of posts, the M&T cross ties between them, the waist-height 'sil' closing out the main portion of the wall with loose insulation*, and the removable vertical planks down at the bottom on the interior covering a plumbing path that can be insulated with foam block as needed (a tacked-down trim strip would secure their lower ends against the floor). One additional benefit I realized mocking it up, is the interior look is likely attractive enough to avoid any additional effort beyond a canned finish (not even that, if engineered wood flooring is used to form the interior planks; only the exterior ones need to be somewhat strong)

*the sil board would be a convenient place to attach window boxes, being joined into the posts at its corners


This is mocked up with 12" thick wall, and a 4ft post span, each post a 4x8. Seems like it could go wider with a properly-designed roof & floor truss system, comparing it to other 8X8 post designs I've seen (especially if the two layers of planks are intermittently buttressed by stick-lumber studs). I hope it's obvious the sizing/spacing of all these elements are entirely improvised; all will be changed when I get to the calculations phase of design.

Also a very rough depiction of how the double-roof sits on the two posts (minus the ties connecting them). As you can see, there is a continuous gap of several inches between the wall and roof layers from top to bottom, even with major rafters jutting out to support a large overhang (and possibly even a vented roof layer). I think the primary practical difference with the Larsen-style truss is that the second layer of wall is not 'hanging' cantilevered off the foundation on the primary posts. No idea if this is advantageous or not, however. It also does not rely on fasteners smile


Edited by TCB (02/14/16 11:42 AM)

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#33476 - 02/14/16 11:44 AM Re: Double-Wall Enclosure Concept [Re: TCB]
TCB Offline
Member

Registered: 02/10/16
Posts: 26
Loc: Texas Hill Country
Please let me know if you are bothered by the large posts (bad habit of mine ;)). Technical discussions like these are always a bit 'fractal,' with each response generating two more lines of thought.

TCB

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#33493 - 02/15/16 11:26 AM Re: Double-Wall Enclosure Concept [Re: TCB]
D L Bahler Offline

Member

Registered: 05/17/10
Posts: 946
Loc: Indiana
I think you could eliminate the double-framed roof as you show it here entirely, and accomplish essentially the same thing by having a 'double roof' as I often have seen it employed in Switzerland. You have your primary roof onto which an insulation barrier is applied. Atop that, you attach strapping screwed through the insulation which holds the roof decking or tiles or whatever you apply.

This same concept is used somewhat less often in North America.

I'll fill you in also on how this system is used today.

First of all, 'Plank and frame' or 'Bohlenwand' techniques are the inferior of the two solid wood infill techniques. The better technique is what I know as 'Fleckwand' which you should think of as a log infill. This technique descends from a hybridization of log and timber building in the sub-alpine regions on the northern verge of the Alps (in contrast to the Bohlenwand or thin plank infill which is simply a timber frame with boards inserted between the framing)

A lot of the Log infill methods actually are not infill at all, the horizontal timbers are bearing the loads and the posts simply secure their ends and create a simpler means of laying out and joining the corners. So it is really a log structure with uprights (not posts, because they don't carry any weight) Though later it evolved into timber frames with log infill.

What some manufacturers are doing today is constructing the log infill as an engineered component, a piece of insulating foam sandwiched between two layers of wood. (I am not a fan of this)

These houses have modest thermal performance without adding any insulation. Even today new houses are sometimes built with heavy log infill and no insulation added. However, when they do wish to add insulation it is applied to the inside. Americans like to have big heavy timbers seen inside the house and a nice wrap around the inside. The people along the northern edges of the Alps prefer to leave the framing exposed on the outside and apply a nice enclosure on the inside. They use generous overhangs (think like 12 feet) to keep the frame dry.

The Swiss sometimes employ a concept quite similar to what you seem to be working toward, only instead of building 2 separate heavy timber frames they construct a light frame on the inside. They don't use this frame to support anything -the loadbearing structure is all tied into the exterior frame.
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#33506 - 02/15/16 06:54 PM Re: Double-Wall Enclosure Concept [Re: TCB]
Jay White Cloud Offline
Member

Registered: 11/06/08
Posts: 480
Loc: Vermont
Hello TCB,

Never worry about length... wink....You have to ask what you are thinking about, and sometimes it can get long...

Originally Posted By: TCB
.../am uncomfortable embracing something so different from what I expect a 'wall' to look/work like..


I can appreciate that for sure...Yet you have explained and shared, "...I simply have no experience..." and as such perhaps should really push past your comfort zones (with current understanding) so no option of consideration is left out...???

Just a suggestion of capacity in scope of comparative understanding. This is one of the reasons folks do hire Architects/Designers and the collective knowledge (and team) they bring with them...

Continued....
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#33507 - 02/15/16 06:58 PM Re: Double-Wall Enclosure Concept [Re: D L Bahler]
Jay White Cloud Offline
Member

Registered: 11/06/08
Posts: 480
Loc: Vermont
Hello TCB,

Never worry about length... wink....You have to ask what you are thinking about, and sometimes it can get long...

Originally Posted By: TCB
.../am uncomfortable embracing something so different from what I expect a 'wall' to look/work like..


I can appreciate that for sure...Yet you have explained and shared, "...I simply have no experience..." and as such perhaps should really push past your comfort zones (with current understanding) so no option of consideration is left out...???

Just a suggestion of capacity in scope of comparative understanding. This is one of the reasons folks do hire Architects/Designers and the collective knowledge (and team) they bring with them...



Originally Posted By: TCB
Historically, folks primarily had wood to work with (think Old Timey Hollywood western town construction), and before that frequently used cut/natural stone & mortar when they needed something more durable.


Wood was employed, of that there is no doubt. I would share, historically the "Hill Country" of Texas was dominated mainly by an equal blend of timber/log, adobe brick, and hand-cut limestone with a very Germanic influence in architectural forms strongly influence as well by the Mestizo modalities of construction.

Originally Posted By: TCB
...this plank scheme is somewhat like Wattle & Daub on steroids, after all...Not even drywall survives the weather swings...


"Plank" infill methods does have some limited characteristics to "wattle and daub," but it is limited. Either is applicable as "drywall" has no comparison in this conversation.

Even a "light daub" system of say a "Bousillage" type would be far more robust than any modern "drywalls," and if you combine this with adobe methods of the region, (along with the appropriate lime plasters) you have an extremely durable system plastering (inside) and rendering (outside) finishes.

None of this is to say a "plank wall" isn't great! I like both equally in many ways... smile

Originally Posted By: TCB
Older pier structures have almost universal foundation problems (lots of foundation repair companies all over).


Foundations in general, in historic architecture, can often present as having more issues than they actually have, and/or suffer from neglect and inappropriate modifications by "ill experienced" over the decades or even centries.

"Hill Country caliche" and the subsequent surface to shallow bedrock formations of this region actually lend themselves nicely to either "raise earth/gravel foundations" and/or "plinth and post" foundations alike. Both have historic precedent and a fair amount of Library of Congress (et al) documents and blueprints exist for study and review.

Continued...
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#33508 - 02/15/16 06:58 PM Re: Double-Wall Enclosure Concept [Re: D L Bahler]
Jay White Cloud Offline
Member

Registered: 11/06/08
Posts: 480
Loc: Vermont
Originally Posted By: TCB
Part of the issue is my present desire is to build into a hillside, which (needlessly) complicates things a bit, in ways our ancestors wouldn't have bothered with, but which I'd still like to explore as an option.


Of all the "indigenous" forms of architecture that may be found in this region, "fossorial forms" are perhaps very german if well situated in a given landscape. Grant you the indigenous cultures took full advantage of natural weaknesses in the topography rather than "digging in" yet the later was done and some other augmentations as well

All in all, I think a "dug in" form of architecture (in the correct setting) would serve you well..IF...well designed and facilitated. I am not a fan of "below grade living spaces" in most regions and by most designs...yet would also offer and validate that when done well, and with vernacular and natural systems, can be one of the most enduring forms of architecture available...

Continued...
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