Thermal-Mechanical Wall Systems for Timber frames and other structures.

Hello All,

I have been reading and enjoying this forum for only a short time now, but find the information refreshing. I'm currently developing a manuscript on traditional building techniques for vernacular folk architecture of the Americas, Middle East, and Asia. Unlike most of the current choices of publications on traditional timber framing methodologies that focus on European concepts, the one I hope to develop, will focus on techniques from many of the older places these vernacular forms developed; places that predate Europe's magnificent wood cultures by thousands of years.

In this endeavor, I hope to examine many of the modern concepts as they have been applied to the traditional building forms. In this post thread, I hope to share and gather further information from fellow readers on "thermal and mechanical envelope noesis." Through sharing and discourse I would like to explore, and take feed back from readers of their observations, thoughts and concepts. I would like to begin with some of the different ideas, new, traditional, and mixed, for enclosing a frame. Lets begin with these, and please add more if you fell I have left any out

Timber frames are, if you will, the bones of a piece of architecture. That skeleton needed to be encapsulated in some fashion, to protect the frame and it's occupants. Brought forward to current standard, and we have the added burden of also needing to provide space for electrical/mechanical facilitation. In doing so, we are at a flux period in architecture where many enclosure forms are being altered to accommodate these necessities, but often the methods of old do not always mesh well with current demands and many of our current concepts, (outside of the labs into a real life scenarios,) do not function as anticipated or in homeostasis with the rest of the architecture, nor the occupants. Vernacular folk structures, in it's simplicity, often, and in many ways, out perform our modern buildings when all the different facets are considered, including the longevity of the building itself and the ability to be adapted to future needs.

There are many "envelope systems" for timber frames. Of these the two major systems are infill and overlay, both have been used in history. Infill methods can include all the modern insulative materials, as well as, traditional, (i.e, cobbling, wattling, adobe, straw bale/mass insulation, sliding panel, etc.) Infill has fallen out of favor in modern times for several reasons, one being loosing the full view of the frame and having to drill through large timbers to run mechanicals, a challenge only faced in recent times; the overlay systems have now gained favor for this reason.

Over lay systems are basically a second structure over the first. This can be construed as a waste of materials or unnecessary, and in some cases it may be. However, if done correctly, it only enhances the buildings structure and longevity. Some system rely on being attached to the frame directly others are "hung" on the frame or rest of an enlarged sill. Non-structural stress skin panels, one of the modern methods have become popular in the last few decades, and for roofs this seem like a viable solution in some cases but not for walls. Over-studing (stick built frame over timber frame,) has also become popular for the DYI builders of timber frames and some of the barn to home conversion projects as well. Over-studing has all the same short comings, in most cases, that stick buildings have. The last system, (my perfered system other than or in concert with infill,) is the "wall truss system," it has so many merits that I will not go into all of them in this post. I just wanted to begin a dialog with other readers and let the conversation go where it will, perhaps spinning into other post threads.

Regards,

jay

Great stuff Jay. I have little knowledge of how other culture's timber framing practices compare to traditional Euro and American practices and would love to learn more. Other than the Japanese, I didnt know that there was too much else out there.

I think an overlaid timberframe is one of the more beautiful, longest lasting, environmentally benign dwellings available. Sucks that they can be so expensive up front but you get what you pay for in so many ways. The ways to "overlay" them is certainly a great thread to be explored in detail.

While Iam sure there are many natural methods to be explored and experimented with, my vote goes to stress skin and SIP panels. They are a very consistent option with many manufacturers making them and a lot of science to back up their performance and durability. Iam curious why you think they make good roofs but not walls because Iam leaning towards the opposite these days..

Youre suggestion of truss walls is great of course. http://www.builditsolar.com/Projects/SolarHomes/LarsenTruss/LarsenTruss.htm is a good example of Robert Riversong's version on the Build it Solar site. My concerns with this system and others like it is: High labor costs and painfully thick walls which can be tough to detail (flashing and trim) and cut down on the amount of light especially on the south sides of passive solar homes.

The best thing about thick, truss walls is that they offer a lot of room for environmentally friendly insulation like blown cellulose. Still, those thick walls really bug me. If the trusses arent built to the exterior (like riversongs) the width eats up an amazing amount of indoor heated floor space contributing to a higher cost per square foot.

Foam seems to be the biggest drawback to SIPS and stress skin panels and I think the environmental tradeoff is worth it. Foam is 95% air by volume. It performs amazingly well in much smaller volumes than more natural materials. Its a very long lived material that could last as long as big timbers if constructed and maintained properly.

Brian Knight has made a valuable contribution.


My thoughts on Structural Insulated Panels are;

I dislike the various formaldehydes used in OSB sheathing, I'm concerned with EPS and XPS and their perspective melting points, off gassing is still debated, decrease in R-value performance with age, unease in routing new utilities and adding window/door jams, delmaination under less than ideal conditions, no historical performance as to long term durability.

Steel skinned polyurethane panels solve some of these concerns, for me it is enough to consider the use of SIPs for walls and/or roofing. But now you've stepping into an expensive product, that's difficult to modify on site if needed.


Truss systems as simply a more "natural" way of accomplishing the same goal, however truss systems are not free from fault either... They're time consuming to build, require relatively skilled labor and construction methods are debated (mostly in moisture control measures). These concerns can be worked through with patience and for me represent a small amount of dedication for good finished product.


I'm doing more reading on straw bale, it's certainly economical and fast, but it's plagued by moisture problems and expansion/contraction air leaks if not constructed properly.




Most of the time I believe the proper choice is in relation to location (RTL, I dig it), straw bale is obvious for dry climates, as is truss for cold, and steel sip where termites are an issue.

Hi Nick,

Truss systems as simply a more "natural" way of accomplishing the same goal, however truss systems are not free from fault either... They're time consuming to build, require relatively skilled labor and construction methods are debated (mostly in moisture control measures). These concerns can be worked through with patience and for me represent a small amount of dedication for good finished product.

Please expand this statement more. I like what you said and what your observations tell you. I might be able to help on the cost and speed issue as well as a few more, but want you to share more about wall trusses and your thoughts on them.

Regards,


Jay

Jay C. White Cloud wrote:Hi Nick,

Truss systems as simply a more "natural" way of accomplishing the same goal, however truss systems are not free from fault either... They're time consuming to build, require relatively skilled labor and construction methods are debated (mostly in moisture control measures). These concerns can be worked through with patience and for me represent a small amount of dedication for good finished product.

Please expand this statement more. I like what you said and what your observations tell you. I might be able to help on the cost and speed issue as well as a few more, but want you to share more about wall trusses and your thoughts on them.

Regards,


Jay

To elaborate on why I feel truss systems are a more "natural" way is that unlike SIP and/or ICF you are not using an energy intensive building material, in other words wood is the more sustainable material...

Difficulty in truss systems is mostly because of the lack of skilled labor that has built them, walls must be straight both inside and out and corners require different construction methods.


People like Robert Riversong argue that a vapor barrier in a truss wall with dense pack cellulose creates problems with moisture retention, that only some form of rain screen is necessary...and I agree. Others argue on where the vapor barrier should be placed, near the interior or exterior walls.


This is strictly my thoughts on the subject, I have no practical experience.

Great Stuff Nick,

Thanks for you response. I'll try and address some of this for you.

SIP and/or ICF you are not using an energy intensive building material, in other words wood is the more sustainable material...

These have there place, but even major manufactures that I have spoke to here and over seas, give this architecture a, and I quote, "twenty year viable economic life span." This has been the theme of several conversations. Not that the foam will break down or anything. Most foams will probably last hundreds if not thousands of years, if protected. They are referring to the type of architecture that these modular and kit home offer in the way of service. Most modern built homes are transit at best. In short foam is good in certain applications but there are viable alternatives to SIP and ICF.

Difficulty in truss systems is mostly because of the lack of skilled labor that has built them, walls must be straight both inside and out and corners require different construction methods.

Other than original design and development, these are pretty simple units. Some of the first were just put together with slab wood off a saw mill. Straight walls are a relative thing, and no not all are straight, some have been built with a slightly oblique exterior profile. Not until you get into jig systems and chain mortising, for mass production like we do on job sites does the system get real expensive in tools and material cost are very low comparatively. Building a straw bail or cob wall is as labor intensive and skill required as building a truss. Corners are no harder than if you used 2x6 studs.

People like Robert Riversong argue that a vapor barrier in a truss wall with dense pack cellulose creates problems with moisture retention, that only some form of rain screen is necessary...and I agree. Others argue on where the vapor barrier should be placed, near the interior or exterior walls.

Robert has some very strong opinions about many things, here is no different. I would not say his observation is incorrect, just that the wall truss was not the issue as much as the "vapor barrier." Homes are being sold and built as "air tight," and many are. This is not a good thing at all. Draft free, yes- Air tight no!!! Most modern air tight homes are going to have problems or rely on expensive mechanical systems to create ventilation. Not a natural build in any way.


Thanks for your interest and sharing your thoughts.

Regards,

jay

Jay,


It sounds as if you've built with timberframe and truss before?

If so, how did you build the roof? Is keeping the trusses straight easier than some make it seem?

I suppose difficulty building the trusses in small areas is relative to the floor plan, with many bump-outs/bay windows/etc with any thick wall will be difficult to build.

I'm in the planning stages for a timber *ahem* barn because my township will not allow me to build a small house to live in while I work on my house.

So I was kicking around the idea of pouring knee wall footers (frost line is 42" here) with foam on the inside for a wall that's 6" concrete - 8" foam - 6" concrete for a 20" thick wall and building 18" straw bale walls up from there. That gives me a lift from the ground and a soild support for the window frames.

There are no permits and no inspection for barns under our right to farm act.

I'm still weighing all my options at this point...

Even'n Nick,

It sounds as if you've built with timber frame and truss before?

I was one of those weird kids that thought work was fun, and found the company of elder folk much to my liking. So I bought my first "fixer upper," when I was 17 years old, (no I wasn't rich...not at all!!...work my butt off and ran "trap line," when fur still was worth something.) After I sold that, I built my first timber frame at 19 on my own little 16 acre farm in South Central Illinois. Been a timber wright on and off ever since (about 35 years,) full time for the last 12 years. Wall trusses are one of the best ways, over all-big picture, methods for creating your thermal and mechanical envelope for a timber frame.

If so, how did you build the roof? Is keeping the trusses straight easier than some make it seem?

If you have a timber frame under them there is no issue. However, I specialize in folk styles, particularly Asian. We often build a double roof system, (I will post photo soon,) so the only thing I need on the roof is traditional skip sheet and slate or standing seem metal.

I suppose difficulty building the trusses in small areas is relative to the floor plan, with many bump-outs/bay windows/etc with any thick wall will be difficult to build.

My average wall truss is 250 mm thick and goes up to 600 mm thick or more. Bay and bump outs aren't really needed with a wall truss system, as you already have that with all your fenestration, and when you do design a bay or such, the almost become "macro rooms," in their own right.

I'm in the planning stages for a timber *ahem* barn because my township will not allow me to build a small house to live in while I work on my house.

I like that part about "the barn." That's funny!!! My first timber frame was a "barn," also. It was very comfortable and oddly enough when someone did show up from the county tax office to look at the "barn," that someone was living in for cheap and not paying house taxes, they got a surprise! I was in it, and next to me was my pig, and drinking out of the sink was two of my goats. When they opened the door to come in, the fox and raccoon I live with ran out....that was a funny day, and my house stayed a barn on the tax role.

So I was kicking around the idea of pouring knee wall footers (frost line is 42" here) with foam on the inside for a wall that's 6" concrete - 8" foam - 6" concrete for a 20" thick wall and building 18" straw bale walls up from there. That gives me a lift from the ground and a solid support for the window frames.

There are no permits and no inspection for barns under our right to farm act.

I'm still weighing all my options at this point...

Good for you. You should take your time and weigh all your options, you will be happy you did. I don't use concrete if I can avoid it at all, and then only sparingly. My first frame sat on a traditional stone plinth foundation. No such thing as a frost line, it's an old wise tail...that contractor folks start telling clients. Does frost penetrate the ground in some areas? Absolutely. Is it the problem, no. Soil type is the issue, particularly clay, and of them bentonite is the "demon" of them all. Even with out ice in it, it can split a rock by just adding some water. Frost in some soils will "heave," most do not. Besides if you build traditional on stone or "stone/rubble trench," you have nothing to worry about.

If I could recommend anything at the moment to you, it would be the following:

learn to use Google Sketchup, and share your drawings with others to assist you.

Tell us what timber framing experience you have.

Straw bail for your area might be good to excellent if done correctly, but might not be cost effective or have that low a carbon foot print compared to others insulation. I doubt it could beat Cobb or cellulose.

When do you plan on breaking ground for this project?

Do you have the tools and heavy equipment?

Regards,

jay

These have there place, but even major manufactures that I have spoke to here and over seas, give this architecture a, and I quote, "twenty year viable economic life span." This has been the theme of several conversations. Not that the foam will break down or anything. Most foams will probably last hundreds if not thousands of years, if protected. They are referring to the type of architecture that these modular and kit home offer in the way of service. Most modern built homes are transit at best. In short foam is good in certain applications but there are viable alternatives to SIP and ICF.

Jay

Does the above mean that SIPS work fine and any limitations are due to the building structure and/or architectural design they're hung on? IOW, SIPS installed on a good timber frame (for example) would give fine service for 100 years or so? Just trying to clarify what your gist was there.

Thanks

Rufus

Hey Rufus,

I have been assured by several close friends that are either Bio or Polymer Chemists that, unless exposed to UV, or some chemical agent, that most urethane foams, (even types being made with soy bean oil,) should last at least a century. Some say longer, but either way by the time they would not render an insulative property, some other form will probably be available. I have even thought that you could just replace it as you had time, if I grew tiresome of it. I buy 95% of my foam as urethane or polyiso, (EPS is no good and not included in this narrative.) factory seconds and recycle product. I have kept an eye on soy based types of spray, but they are a few years out still from being truly viable, IMO.

As far as Stress Kin Panels and there related species, I don't have much use for them and only use them on roofs...not walls. I even but those as factory seconds and but them on my saw mill just to remove the OSB and get to the foam. I just don't think in the big picture they are worth the effort for walls. Yes, they go up quick, but then what? You can't run wire in them easy, you can modify them easy, and you definitely cant add something at a later date like a light switch or wall lamp with out making a mess. With wall trusses, you can design a wall panel system that you pop off and there you go, change what ever you like...and your done. One of the contractors I work with added a wet bar to an office years ago that would have taken some time to do, but with a wall truss system, all that was need was to pull wire and plumbing in less than a few hours and installed the "bar cabinet." Nothing could have been easier or faster.

I still would prefer all natural and traditional insulating methods, but sometimes modern ain't bad.

Hope that helped,

Regards,

jay

Hope I'm not digressing too far here...


Jay and I have a few things in common, I started working at 14, married and bought a house at 17 and never have found much in the way of kindred spirits with my own generation, there is far too much to learn from our elders to be distracted by our peers.

learn to use Google Sketchup, and share your drawings with others to assist you.

I have a 2D CAD program, but that's basically pointless for designing a rectangular building... 3D (like sketch up) would allow me to design the timbers, but I haven't done any design work because I am unsure of the real life practicalities and limitations in timber frame sizes and details.

Tell us what timber framing experience you have.

I've watched somebody drill and chisel a mortice on YouTube, I think that gives a pretty good summary of my experience on the subject! haha

Straw bail for your area might be good to excellent if done correctly, but might not be cost effective or have that low a carbon foot print compared to others insulation. I doubt it could beat Cobb or cellulose.

Dense packed cellulose is my preferred choice, stawbale is just something I have been recently entertaining. I would like to have a stone belt with cedar board and batten, so that would discard strawbale. But does vertical board make sense on a truss wall? Maybe I should stay with a horizontal siding like shiplap or clapboard... or am I just over analyzing the actual build?

When do you plan on breaking ground for this project?

May-June this year.

Do you have the tools and heavy equipment?

Plenty of tools (none specific to timber framing) and more than enough heavy equipment (bulldozer, front end loaders, skytrac, etc.) but to tell you the truth, even though I want to learn the craft for myself and have the experience of building my own house barn... I'm going to hire a skilled wright to build it and help him/them with the raising.



I've spent most of my time thinking about future use for the building once we're moved into our permanent home, most likely it will be used as a workshop and/or guesthouse.

I've always had a soft spot for wood working, just never had the space, so that's very likely what it's main function will be. It could also serve as a room and board for people doing workshops or volunteering on the homestead, if I ever go down that route. So enclosing the loft would be great to have as a finishing room, but it would defeat some important features I'd like to have, such as good air stratification/circulation and evenly distributed solar gain. Building would be oriented east/west longways with a gable roof, and lean-to (porch) on the north side.


My gut tells me to go with a 20'X40' or 24'x36' full height 2 story with a 2/3 loft on the north side, it seems like a good compromise between the space of a full loft and air circulation of a 1/3 loft.

I could also build a saltbox with the high wall to the south and a dormer on the north end, if I wanted a smaller loft in relation to the buildings footprint... But then with the long roof going into a lean-to it would be like one big ol' ski jump of a roof.

I'm also mulling over the idea of installing a glass house on the south side to see how well solar gain storage works in the real world... So many theories to test before I build my actual home.

Hi Nick,

As long as we get you into a house with wall trusses, digress all you would like...if we get to off track, will just start a new post thread about your timber frame aspirations. Sounds like you and I have similar relationships with the generation behind us. Now I'm in the behind part, finding young folk like you more often...keeps me young and saves the stuff handed down to me from being lost.

Get the Sketchup, and learn it. It's really a great program, everyone has it now and is learning it, even some public schools. Don't worry about not knowing timber framing, you just design and put up for critique.

Dense packed cellulose is my preferred choice, stawbale is just something I have been recently entertaining. I would like to have a stone belt with cedar board and batten, so that would discard strawbale. But does vertical board make sense on a truss wall? Maybe I should stay with a horizontal siding like shiplap or clapboard... or am I just over analyzing the actual build?

Dense packed cellulose is an excellent first choice. I have seen some sawdust fill walls that are over a 150 years old, and warm as can be. No vapor barrier, just nice packed saw dust in an 8" thick wall and lath with lime plaster. Cellulose is just a step up and better insulator.

What do you mean by "stone belt?" Is that something to do with the foundation?

Vertical wood siding is always going to be better that horizontal. Wood likes to run in the direction it grows. Another way of thinking about it is, which last longer a standing dead tree or one on it's side? We can get into grain orientation as the like later. So in short, my wall truss are most often covered by Vertical siding, because not only do I build "cold roofs," I time my walls in to them and that makes them a traditional "breathing wall."

May-June this year.

Boy...you got a lot to do!!! Do you have to build this year, seems like a lot of learn'n to do first. It's doable, but that grind stone and your nose are going to become real good friends.

I'm going to hire a skilled wright to build it and help him/them with the raising.

Do you have one in mind?

Do you know what to ask?

Do you no your area's market price for timber frames?

Do you no your area's market price for turnkey project?

Much to consider, you should send me a private email or give me a phone call.

Regards,

jay

What do you mean by "stone belt?" Is that something to do with the foundation?

Simply aesthetical, to match the stone wall needed on the south side for thermal mass. The idea is to use a glasshouse to heat the stone in the winter and open the windows and doors from the glasshouse into the house to circulate the warm air, in the summertime the heat is used to create a passive vacuum from the shaded northern lean-to through the house and up out of the ridge vent of the glasshouse.

There are many ideas like this which are perfectly sound logic, but the practicalities are still debatable and even though it may work great for somebody in Colorado doesn't mean it will work effectively in Michigan. So this project is essentially a test mule for the actual house, to take good ideas and see how they work in the real world.

Vertical wood siding is always going to be better that horizontal. Wood likes to run in the direction it grows. Another way of thinking about it is, which last longer a standing dead tree or one on it's side? We can get into grain orientation as the like later.

Seems perfectly logical. My initial thoughts were on the extra labor/lumber needed horizontally, but I suppose since it isn't holding anything other than the siding/cellulose that 1x3 at long intervals would suffice... or do you use plywood/osb for sheathing?

So in short, my wall truss are most often covered by Vertical siding, because not only do I build "cold roofs," I time my walls in to them and that makes them a traditional "breathing wall."

By cold roof do you mean there is an attic with loose cellulose blown in? I'm curious how the junction from the wall truss to the joist looks like, I can't picture how it would work without a top plate?

Boy...you got a lot to do!!! Do you have to build this year, seems like a lot of learn'n to do first. It's doable, but that grind stone and your nose are going to become real good friends.

Me, me personally could live in a garden shed for 10 years before I finally got the gull to build something... It's the wife that's crackin' the whip. I don't have to finish soon, just start soon

Do you have one in mind?

There's some people who I've found, but have not contacted yet. I'm hesitant to commit to anyone/anything before I fully wrap my head around the project. That and I know what it's like being on the other side of the table, and what I like to see in a customer.

Do you know what to ask?

Nope.

As far as the actual product goes, I've picked up a little along the way from my father who would work forestry in the winter... various oaks and walnuts for veneering mostly. The person who he's worked with has a mill (I forget type and size, but I would consider it an 'adequate' self driven unit) and depending on where/what he's logging may be able to provide the timbers. The mill is literally less than a mile from the property.

Do you no your area's market price for timber frames? Do you no your area's market price for turnkey project?

High, higher, and highest? Arm, Leg... Honestly, all I have heard are "turn key" prices from $75 to $250 "a square foot" and we both know how completely irrelevant that statement can be.


I work with big box home builders (the kind that are building spec houses at $45 a foot!!) and so I have good ties with people in the industry, so the two things which I am certain I will need help with are the truss walls and timber frame. The rest of it I can handle, well actually I have an uncle that's a plumber and a cousin that's an excavator so my hands are tied there

Much to consider, you should send me a private email or give me a phone call.

I'll take you up on that offer...

Jay

Thanks for the clarification. It sounds like the construction details of foam make or break it. I've read one story last fall (Fine Homebuilding, I think) where a contractor describes tearing into a super insulated A-frame shop w/insulated roof he made five years ago to check and fix a few things. From what he said, the foam panels he used under the roof actually shrank a small fraction of an inch - enough to let him see the seams clearly on a frosty morning (from outside). I don't remember whether he taped the seams or foamed them tight when building. IIRC he did all the right things and then found there was a clear flaw in the system. He went with foam again, but I think he sandwiched thinner boards and offset all the seams.

Rufus

Makes sense, if foam is 80%-95% air then the majority of it wants to expand and contract with tempature.

Taping obviously is a good ideal, but I have to wonder how long the adhesives will last. Sandwiching offset layers seems to be the most fail proof way.

Hey Nick,

I agree 100%, adhesive in most tapes is worthless after about 20 years. You might get more for the expensive type, but why bother, offset your joints as you suggested. Mechanical/Geometric solutions are always superior in most cases.

Regards,

Jay

Hi Folks,

Sorry to arrive so late to the party! I have been hanging out in the Hugelkultur & Energy threads for a few months, and didn't see this topic.

To Jay's original question: I live just 20 miles north of you in Newbury, where we recently built a straw bale home with a recycled Hemlock timber frame. (I used to live in Thetford, and actually met you when out for a winter hike up at the very end of Houghton Hill Rd. about 10-12 years ago...) This is a New Mexico style (timber supported roof) with a straw bale wrap, so the entire frame is exposed to the inside. Passive solar design with black concrete floor; radiant tubing installed, but not yet used. Lots of little technical details are found on my outdated blog, which was originally written to document how natural builders and high-tech zero-net-energy builders could find a middle ground, and was abandoned before we got to move in because I lost my camera, so it needs updating! Straw Bale Blog is found here: http://vtstrawbalehouse.blogspot.com/ Maybe after I get my taxes finished, I'll post a few badly-needed updates!

Timber Frame: The frame was salvaged from the former 431 Main Street in Rumney, NH, built abt. 1850, which was being demolished, so a local timber framer from Warren, NH was engaged to take it apart and bring it here (~40 miles), and re-use it for our new home. Original frame was 20 x 40, and our plan was for 30 x 30, so the longest beams were cut down, and we used the long axis running east-west, and added a 10' shed-roof extension to the north. The largest parts of the original frame were 6 x 8, and since we needed to add some additional timbers anyway, we got some 8 x 8's from a barn being torn down up in Peacham, VT, built in the 1880's (18 miles away). We ended up using 8x8's for all the corner posts, both for looks and for added strength, since we were planning a masonry heater (yep -- RoyWood, another connection), and wanted 10' ceilings for good convective flow.

Straw Bale Walls: The original contractor really didn't know squat about making bale walls work in this climate, so we ended up working with Ben Graham (Natural Design-Build), and Ace McArleton & Deva Racusin (New Frameworks Natural Building), who are probably the most knowledgeable and experienced active straw bale folks in the Northeast (I understand Paul Lacinski is no longer building houses, and he trained these folks years ago). Between the bales and the ground we have a 4' x 4' rubble filled trench (w/drainage to daylight and a 4' wide x 2" sheet foam skirt to prevent frost penetration), a moisture barrier, a 9" tall by 22" wide R-20 ICF concrete beam, a wicking break, then an 18" concrete block "toe up" filled with pearlite and vermiculite (insulated on the inside with a 1" air space, a 1" foil-faced foam layer and 6" of dense-pack cellulose), then another wicking break before the bales are stacked on edge. Site-mixed earthen plaster made from clay, sand, chopped straw and cow manure applied inside and out, with different amounts of clay and lime in the various external layers. Lime wash and lime paint on outer surfaces, and milk paint on the interior. We opted for exterior corner boards, so the exterior walls look a little too straight for a straw bale home, and while I like the framed look, I had actually hoped for slightly wavier walls!

Roof Structure: Main 20 x 30 part has 12/12 metal roof, giving us ample headroom for a somewhat narrow 2nd floor with 3' knee walls (where I am sitting now), and a 5/12 shed roof over the northern extension. The original rafters were 3x5's, so to these we added a thin foam thermal barrier, and sistered them up with 2 x 12's, with 5/8" AdvanTech on the outside, and 1/2" plywood on the inside, giving us 16.5" cavities which are filled with dense-pack cellulose. Shed roof to the north is made from 4 x 16 I-beam trusses, same sheathing & roofing, and also DPC insulation.

Air Sealing @ Wood-Straw Interfaces: This team is into high performance and very low air infiltration, so a number of measures were taken to get a good seal between wood and straw, many details of which are shown on the blog. The most obvious is 6" plaster "air fins" made from wet location drywall around all the framing, which is attached to the outside of the frame with 5/8" strapping and caulking, which gets incorporated into the applied earthen plaster, so there's a slightly flexible, relatively air-tight junction joining the bale walls to the frame. Where the bale walls meet the roof structure on the north and south sides, the top surface of the bales are sealed with hand-applied plaster, and then in direct contact with the DPC insulation. Strips of Bituthene were used to seal wood-wood junctions inside and out. Cellulose was blown in at 4-5 psi, so all interior sheathing had to be screwed -- not nailed -- since that comes out to something over 500#/sq. ft., which would pop the plywood right off the rafters if nailed!

Plumbing, Wiring & Mechanicals: We had to think through our plumbing and drainage (greywater) since those PVC pipes were laid down before the concrete floor went in. Depending on the floor plan, the same may apply to the wiring. In our case, we had to allow for 2 1" PVC conduit runs to run wires under and through the floor. Most wiring is run through interior stud walls (stick built), and wiring for exterior (bale) walls runs through the 6" space inside the toe-up before the DPC insulation is injected, which worked great! Wall switch boxes can be mounted into cut-outs in the bales with wooden pins, and many people run standard Romex or UF wires in the bale walls with no conduit. Natural plasters do not seem to cause a problem with the plastic coatings. We opted to run small pieces of 3/4" conduit up to the wall switches, mostly so we could pull the wires out, or run other wires later, if needed. We only have 4 duplex boxes mounted directly into the bale walls, and the rest are attached to the stick-built walls.

Important Little Detail we DIDN'T do: Most timber framing is done with the wind bracing to the outside of the major frame elements, presumably so it would be easier to fasten the outer sheathing (which would also help with rigidity of the structure) . For straw bale work with the frame exposed, it makes more sense, and saves considerable labor, to place all these braces on the inside edges of the frame. Then when the bales and plaster are applied to the outside (as a wrap), there are many fewer interfaces between bale walls and timbers, so fewer potential leaks and shrinkage cracks, and the hand-applied plaster goes a LOT faster without all those $#@& little triangular spaces to work in and around, and 4-5" of room behind them for hand work around the posts.

Performance: We moved in about October 1st 2011, so we are just wrapping up our second winter in the house. We are heating exclusively with a small Napoleon woodstove (the radiant tubing is in place, but not being used yet). We used a little less than 2 cords of wood last winter (pretty mild as Vermont winters used to go), and 2 cords this winter, which was significantly cooler. New Frameworks & Natural Design-Build got a grant to study the thermal performance of a number of the structures they had built over the past 4-5 years, so I have blower door and infrared info on this building, as tested before completely finished. I would have to hunt for that report, and intend to post that on the blog. We have a few small air leaks that I can address with a little caulking, and I've noticed a little bit of 2nd year shrinkage around some of the windows that can be readily sealed up -- probably from the "KD" pine drying out, not from the plaster shrinking). I've chosen to leave those be for now, since we don't have any mechanical ventilation, and I have not installed the insulated outside "make-up" air tube to the woodstove, so we are drawing a little fresh air in through these leaks during the heating season. I will probably forgo the Venmar Eko-1.5 HRV that was planned, and just opt for a Panasonic point of use air-air exchange fan for a bathroom exhaust, and shave an inch off the bottom of the bathroom door once these leaks are sealed -- or maybe not.

Anyhow, a VERY long response, but it seems this thread is into exploring some of the details of how different forms of natural building actually work, so I hope it has been helpful, and not too tech-y/geeky! We're much more comfy burning 2 cords in this house than we were burning 5 - 6 cords in a 650 sq ft cabin on the property, and now we're returning to our focus on permaculture and hugelkultur, and learning ow to use our root cellar.

BTW: I'd also agree that Robert Riversong has some very strongly held opinions, but he knows quite a bit, and in general, tends to steer people away from far more wasteful ways of living, so he's been a positive influence on many people, and a good friend of the planet. I'm also not a fan if Stres-Skin panels and SIPs, since I think there are very few builders who take the time and extra effort to install them correctly, and if they haven't thought through all the moisture management issues, moisture stops dead at the foam, and the plywood can get wet and rot.

Hey Brad,

That was great, thanks for the update!

Regards,

jay

So Jay tell me why you prefer XPS to EPS for a foam? I'm currently drawn to EPS because it is vapor permeable

Also OP if you are going to go with a concrete foundation why put the insulation layer on the inside of the concrete? Why not on the outside so you can isolate the thermal mass?

I'd love to fund a material other than concrete for foundations but in my area it seems to be the only thing that will structurally stand up to our soil. Brick, wood, stone etc all fail here under the pressures. I will say that the stone doesn't necessarily fail as in the house falls down but it fails in that the house heaves and the foundation walls disintegrate.

If I could figure out a foundation that could be thermally broken from the surrounding ground while still providing a LARGE amount of thermal mass for my climate I'd be stoked. The effects of thermal bridging on foundation walls here are extreme and further north its even more so. Common problem here is our winter frost line is up to 8' so foundations that leak heat keep the earth around the building thawed and the foundation is basically swimming in clay while the surrounding clay is frozen solid. I'm looking at cob on rubble but its not really structural and there is very little real data on it.

Hey Sean,

Can you tell me more about the foundation demands of your region? Is it simply a greater frost depth than most people design for, or is there also movement or other forces acting on foundations that complicate things?

We do not have a traditional poured foundation under most of our house, though we do have a 10' x 15' section with an 8' tall "basement" for the mechanical room and root cellar, and this is made of R-20 ICF, with 2' of crushed stone below it, contiguous with the drainage system around the entire structure. We use a 4' x 4' rubble filled trench with fairly coarse stone (4" minus) drainage and 4" perforated drain pipes at the bottom of the trenches protected by filter fabric, and so far (about 6 years since it went in), everything has worked very well. The whole system drains to the low point below the root cellar, and then sloped 1/4"/ft to daylight -- we just happen to have a steep bank to the west that allows us to drain everything below the basement level. The wall system is supported by a 22" wide, R-20 ICF "beam of concrete that's 12" high.

We also protect the Rubble Filled Trench (RFT) from frost penetration with a 4' skirt of 2" foam boards sloped a little bit away from the structure, and attached with a little Great Stuff expanding foam to the outside of the ICF beam.

I believe RFT's have been used successfully in very cold climates with deep frost penetration like you have. My shoot-from-the-hip best guess would be to extend the foam board skirt out to 6 or 8 feet, to help keep frost from getting down below the protected zone near the ground level -- but that's just a well-educated guess. I know that foam insulation has a list of nasty characteristics for green builders, but might be an example of a toxic product, manufactured from petroleum, that could be seen as appropriate because it saves so much energy when used carefully and wisely (?) We do need to exercise great care in dealing with and eliminating waste, which can end up polluting water, and floating in the Pacific for generations to come -- if we survive that long.

I would say that our code doesn't really reflect our frost depth but we also have movement because our ground has a high water table and is mostly clay. Basements are under a lot of stress in our climate and even the old stone basements are falling apart. Our temperature fluctuations between summer and winter are also pretty extreme so we have to account to the effect of temperature on the shifty soil.