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Post placement with scoria bag foundation

 
Patricia Sanders
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Location: St. Johns, AZ
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Hi! Designing a small straw bale house (rectangle, 11 x 18 ft i.d.), modified post and beam as described in THE STRAW BALE HOUSE (i.e. door and window bucks are load bearing), with a scoria bag foundation. The Steens recommend a post at each corner. I will set these posts on a stone or concrete punch pad below the rubble trench.

Simple question: If the posts are set into the corner bales, the scoria bags need to accommodate the post somehow. I haven't worked with bags, but it looks like they are not that easy to force into a shape like around a post. So, specially sewn bags? Mini bags to fill in the spaces? Adobe bricks?

OR the posts could be positioned external to the corner. Which would save me from notching corner bales, but might slightly complicate the roof framing (conventional hip roof).

Are walls more "solid" with the posts set in?

I have zero experience with straw bale building and working with bags, so would appreciate comments from people with experience.

Thank you!

Patricia
St. Johns, Arizona
 
Jay C. White Cloud
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Hello Patricia,

I will do my best to be of assistance with what seems like perhaps a rather challenging design for a "first time?" DIYer design-build project.

Are walls more "solid" with the posts set in?


It all depends on what style of timber framing modality is being employed...infill, exterior frame, or interior frame armature system? These all have applicability with there given pro/con perspectives. Strength is derived in the wood joinery used for the build, and its bracing style (oblique rigid or horizontal flexible system.) If this isn't a "timber frame" but a "post and beam" structure with metal fittings and fasteners then it really needs to be either inside or outside the wall mass materials, as the metal does not react well to encapsulation within the give wall matrix of wall, no mater what type that ma be (i.e. SB, Cobb, Adobe, Stone, Brick, etc.)

Has this design been examined by a PE or other professional Natural Builder? If not, if I may, I would suggest it at least get a cursory review for safety and/or easing the building process.

Regards,

j
 
Christopher Steen
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Patricia Sanders wrote:...Simple question: If the posts are set into the corner bales, the scoria bags need to accommodate the post somehow. I haven't worked with bags, but it looks like they are not that easy to force into a shape like around a post. So, specially sewn bags? Mini bags to fill in the spaces? Adobe bricks?

OR the posts could be positioned external to the corner. Which would save me from notching corner bales, but might slightly complicate the roof framing (conventional hip roof).

Are walls more "solid" with the posts set in?
...
Patricia
St. Johns, Arizona




You can easily tamp scoria bags with a tight wrapping butt joint, much easier than notching bales. however, i found detailing and thermal performance to be more complicated by setting posts in the wall and infilling bags/bales. I personally prefer setting posts just interior to the wall to simplify bagwork, balework, and post setting. it also gives you an easy method of attaching interior walls, shelves, cabinets, etc. the exposed timber aesthetic. you also get to keep that running bond bale corner for shear strength. also, it allows for simplified bale compression when strapping down your top plate/box beam before post attachment...

I reckon with that small of a sized building, even with your snow loading, a tradition hip roof sitting on quality load bearing (on edge) bales would produce a pretty solid house, even before your structural plaster skins. but i'm not charging for my advise...

i like the hips, but know that the traditional hips are a complicated roof to frame.

either way, remember to buttress your exterior bag corner until plaster to prevent corner droop.

that's all i got. Jay, i'd enjoy reading your thoughts on internal/external/infill frame sometime.

chris
 
Jay C. White Cloud
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I personally prefer setting posts just interior to the wall to simplify bagwork, balework, and post setting. it also gives you an easy method of attaching interior walls, shelves, cabinets, etc. the exposed timber aesthetic.


By far, my preferred and recommended system for all...other than perhaps traditional vernacular timber framing style reconstructions, or double wall/roof framing systems.

Any bagged materials or bales should strictly be "self loading" to themselves alone and carry no other dynamic loads from either the wall or roof diaphragms, unless the structure has been thoroughly engineered by a PE and/or Professional within this type of building modality. I share that as a professional prospective and caveat that too many approach "structural bag and bale" architecture without the prerequisite structural design understanding to render safe buildings in my view of safety margins and good design. Just a shared safety perspective...

Jay, i'd enjoy reading your thoughts on internal/external/infill frame sometime.


External, is more an "aesthetic choice" and one I tend not to care for from both structural and maintenance/durability reasons. Though, with good maintenance and roof overhangs, they can be quite nice.

Infill systems are historically and still today from a global perspective very common and dominate in some regions.

Encapsulated systems should not have any metal but can have less quality joinery and attention to timber framing details as the framework isn't viewable after completion. This also is an issue when it comes to "visual inspection of the "super structure" or needs for maintenance.

Internal, as stated above, is my preferred. I do also like double wall systems, and/or wall truss systems. With forms of these you can get the "traditional "infill" aesthetic, and the internal aesthetic of timbers within the living space This renders a wonderful ambiance and thermal mass the timbers offer in the way of "thermal dampening" within the given desirable ambient temperature range.

Regards,

j
 
Patricia Sanders
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Location: St. Johns, AZ
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Jay, Chris,

I'm VERY grateful for your attention to my question and your comments. I'm sorry to take so long replying - I'm helping out on a farm and don't have a lot of leisure time.

I'm tending toward external corner posts because I'm going to wrap the house with porches/verandas so will need exterior posts anyway. Also the interior is so tiny, I'm loathe to give up any space at all.

To clarify, the "modified post and beam" system I refer to is, essentially, building the window and door bucks to extend from the foundation to the beam so that they serve as structural supports. Bucks consist of box columns the width of the bale wall made of 2x lumber sheathed with plywood or OSB, with additional support under the beam. My plan has two windows per short (14') wall and one window and one door in each long (21') wall - plus corner posts. THE STRAW BALE HOUSE describes this system as efficient in cost, materials, and labor, and it does seem to me an elegant solution.

Jay, your point about this being a challenge for a first-timer is well taken! I might just be overconfident in this case. I'll get the plans looked at.

Many thanks,
Patricia

 
Jay C. White Cloud
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No Worries Patricia, I am here for you and the other readers as much as I can be, and understand having "too much" on one's plate at certain times to be as "responsive" as I would like to be.

I'm tending toward external corner posts because I'm going to wrap the house with porches/verandas so will need exterior posts anyway. Also the interior is so tiny, I'm loathe to give up any space at all.


That is more than a good reason to go with the "external format" for such a build. I understand and agree with your reasoning completely. If the space is demure in size, as suggested, you are not losing much in the way of "thermal storage" by placing the timbers "outside" which in turn will facilitate a much more easy build of the veranda area and offer some very beautiful aesthetics to this living space and the external affect of the structures presence on the landscape.

To clarify, the "modified post and beam" system I refer to is, essentially, building the window and door bucks to extend from the foundation to the beam so that they serve as structural supports. Bucks consist of box columns the width of the bale wall made of 2x lumber sheathed with plywood or OSB, with additional support under the beam.


That will work fine... and if you are comfortable with that...go for it.

I can think of several modifications that are perhaps more robust and or traditional with the "bucks" actually being smaller scale Asian style "post and lintel" timber framing, and/or a "wall truss system" that also forgoes the plywood/osb and employs all wood joinery.

Either way, it sounds like you have a good to excellent start for achieving your goals...

Jay, your point about this being a challenge for a first-timer is well taken! I might just be overconfident in this case. I'll get the plans looked at.


I don't believe you to be "overconfident" at all, as unlike too many DIYers out there...you have actually sought out feedback from an open forum, and that speaks volumes to being open to an exchange of concepts and approaches. Taking this time to listen, and be patient with yourself (and the "plan") is vital to a good build, and it seems you are on your way. If you had some drawings (or a CAD model) of the plan that would add others in really being able to give more thorough feedback.

Regards,

j
 
Judi Anne
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JC, would it be an inconvenience to link an example of what you called "double wall systems"?
 
Jay C. White Cloud
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Hi Judi,

There are already several great discussions here on Permies.com that cover this, and many others as well from foundation types...to "breathable walls." If you have any additional questions, feel free to ask...

http://www.permies.com/t/19798/timber/Thermal-Mechanical-Wall-Systems-Timber

http://www.permies.com/t/46846/straw-bale-house/Framing-clay-slip-chip-walls

http://www.permies.com/t/47431/natural-building/Natural-building-hill-slope#379639

 
Judi Anne
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Excellent. Thank-you. Reading away. Trying to formulate the questions I need to ask about our design direction.


So double wall systems is another way to say a wall truss system?
 
Jay C. White Cloud
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So double wall systems is another way to say a wall truss system?


Aye Judi, exactly it is just that... I look forward to your future query...
 
Dean Howard
Posts: 112
Location: NE ARIZONA, Zone 5B, 7K feet, 24" rain
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Hi, Patricia. Dean, here... Looks like were neighbors... I'm just down HWY 61 toward Vernon. I'd love to see the project and help out a little, when you need extra hands, just for the learning experience.

I'm a bit curious... post and beam construction stands on it's own. Strawbale structures, when built in load bearing fashion, stand on their own...no matter the foundation.
To me, it does seem overly complicated to try to tie in posts, bags, and bales, then cover them all with stucco, or clay/lime rendering and have them all expanding at different rates. Just a thought.

I'm pretty sure the standard strawbale house get's tied down to whatever foundation (cement, bags, laid stone, block). I've never like the thought of just using bales as infill, mainly because of the expense of building a frame house, then adding bales, when compressed bales are extremely strong, and are known to last centuries when built properly.
 
Jay C. White Cloud
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Hi Dean,

If I can, perhaps I could address a few of your points, and maybe it would make a bit more sense...or not...but I will try.

I'm a bit curious... post and beam construction stands on it's own. Strawbale structures, when built in load bearing fashion, stand on their own...no matter the foundation.


Now I may have confused things a bit, or not understood the meaning (forgive and correct me if I have) but the "glitch" with the quote is..."no matter the foundation." Foundations are well beyond critical, and actually, other than the roof to protect everything, the foundation is the most critical part of architecture.

For DIYers, timber frames and/or post and beam structures may seem harder (and in ways could be considered so) but they are actually less prone to issues than "structural SB," if long term and durable home building is the goal. So I believe that is what Patrica is going for...the structural firmness and durability of a timber frame and the thermal mass of SB.

To me, it does seem overly complicated to try to tie in posts, bags, and bales, then cover them all with stucco, or clay/lime rendering and have them all expanding at different rates. Just a thought.


I think we already covered in this the posts above the different potential modalities of this type of framing system and I shared...from research, experience and observation why I made the recommendations I did. Patrica is opting for an "external framework," which I commended her on for her specific goal sets. Further, stucco is a OPC based material and not at all recommended for this type of architecture as it promotes rot, traps moisture and is generally a very inferior material compared to traditional lime and/or clay renders. When designed and built correctly differentials in expansion between the thermal diaphragm and the superstructure is insignificant and/or compensated for. Hope that made sense and did sound to "techie' for a reply.

I'm pretty sure the standard strawbale house get's tied down to whatever foundation (cement, bags, laid stone, block). I've never like the thought of just using bales as infill, mainly because of the expense of building a frame house, then adding bales, when compressed bales are extremely strong, and are known to last centuries when built properly.


I can more that accept and appreciate that view, and if someone does have a number of builds under their belt, has designed different forms of natural buildings and different structures types with little issue or challenge, I see no reason not to attempt a "structural SB."

As a professional builder and teacher of same, I can't in good faith recommend to novice or limited experienced builders to attempt a structural SB. Some pull it of, many do not. I would also share that as a seasoned builder I, myself wouldn't typically build a structural SB, because no matter the style they can never be as strong or as enduring as a timber frame and SB combination. SB or SB with wall framing both have to have sturdy roofs. The added expense of some wall framing that also accommodates the fenestration of the architecture adds little to the cost of the building and ensures a robust structural format and over ease of building other elements like her engawa.

Hope that made a bit more sense...

Regards,

j
 
Dean Howard
Posts: 112
Location: NE ARIZONA, Zone 5B, 7K feet, 24" rain
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Hi, JC; Knowing you are a builder does put some light on your comments. Most builders of anything, would rather shoo away the novice...I'm not putting a negative emphasis on this, by the way. But, it seems Permaculture is begging for the novice to try things, and therein lies the rub. Most books I've read on the subject give great advice and use proven techniques...the application of which is only as good as the workman... I'm definitely with you on this.

As far as the modern day farmer/permie, with diligence, we can do what old cultures and seasoned farmer/builders have done... I look at it in the light of: Thousands of Strawbale homes have been built before this country was even established... I would venture to say most are still standing. I really don't know how/when the current, compressed bale wall developed, but with sole plates, top plates, rebar ties, cement caps (don't know the term for this), there is every bit as much structural integrity to the walls that support the roof, as there is in a timber framed house, in my opinion... with the roof being the same ie; trusses.

Jay C. White Cloud wrote:Hi Dean, Further, stucco is a OPC based material and....j

I guess I was thinking of permeable stucco coats that breathe... I know they hairline crack enough to breath plenty, but covered in paints that don't breath....yea, moisture, rot, etc.

It is always best to rely on others who have gone before us with any application of technology, and I do see signs of this, and am encouraged. Funny, though, I think I also like the Paul W. method sometimes. He's a thinker, tinkerer, and engineer, and he charges ahead with his own plans, schemes, and designs, because sometimes, it's just plain fun to try things. In Patricia's case, this is just slightly bigger than an undocumented shed built without an engineering stamp....but, the operative word is "bigger" and "living space"... calling for some design review as required.
 
Jay C. White Cloud
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SB is, historically speaking, a relatively "new concept." The steam-powered balers of the late 1800s made straw harvest and compression into bound bales easier. From this was born "transient structures of "baled straw," not meant to last but get a family through till better buildings could be build...similar to "sod houses." As time progress though, some forms and methods did improve and we saw more enduring forms of both sod and SB. I have written on a few posts about this history. In early 1900s to about the 1950s, SB did become more common and only today are we seeing a similar resurgence. Most "are not still standing" because many were ruined after lime and clay renders fell out of favor for what many "thought" was a better way. "OPC Stuccos" which rapidly decayed many of these buildings some of which had been performing well for over 100 years, turned out not to be such a good idea, and this lesson still hasn't been learned.

It has been my experience in both research, examination and building that "OPC" and its application (especially with rebar and the "rust jacking" issues it has in it) doesn't have a very good track record of services, and seem to do much more harm than good to SB structure that are built with it. Some in very dry/desert regions seem to be surviving, but none of these are historic structures and less than 50 years old. Timber frames present with a much longer history and structurally have a framing system that statistically is more enduring than most modern methods in general and especially with SB architecture.

Even among "modern" concrete and steel structures of today timber frames outlast and outperform in all manner of ways it would seem. Many modern opc steel reinforce structures seldom have an economic or viable life span much past 30 to 40 years, on average. This is illustrated in the rapid decay of the concrete and steel infrastructure like roads, bridges and related architecture that is failing in both as the metals oxidize and the concrete in turn spalls and loses more structural integrity. Historically modern OPC has not matched the strengths of historic geopolymers, pozzalonics and natural cements of the Romans from over 2000 years ago. The Pantheon is a living testament to this ancient wisdom in "good practice" of lime based reslidifirers, and in means, and method application.

I have seen and experienced, while listening to many SB builders (DIY and professional) that structural SB is much more challenging to get correct for a good long term build. Having a superstructure of wood (never concrete evidence would suggest) is much safer and easier to achieve (big picture view of project) than trying to achieve solely a SB structural build alone, as there is much to consider when we ask a SB to support the roof and the wall diaphragms other configurative demands.

Stucco, was at one time, and very interchangeable word applied to any type of parging, render or plaster. It grew to mean a parging only on the exterior of a structure comprised of OPC cements. These whether painted or left as is, even if containing micro fissuring do not breath. OPC cement acts like a sponge and hold on to moisture as it is a very saturating medium with strong hydrophilic characteristics. Lime and/or clay renders, and plasters alternatively, act as a "drying poultice," thereby effectively move moisture away from SB wall systems.

I am all for "experimentation" and trying new things...but feel that in designing and building a primary residence or a major project undertaking, it may not be wise to take such risks or recommend such modalities.

Regards,

j
 
Patricia Sanders
Posts: 17
Location: St. Johns, AZ
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Just a postscript/update here. Dean, sorry to take so long replying - I will PM you.

I spent a day at Canelo since last posting and am inspired now to build a "teensy" house first, prior to the above-described "tiny" house, to learn and practice the skills. The teensy house will have approx. 10x12 footprint but very similar construction to the above described.

I'm planning to spend another few days with the Steens on a build in SE AZ before returning to my place - great chance to see their current methods, and I will post about that, assuming they're okay with it.

Thanks, Dean and Jay, for the interesting exchange.

Patricia

 
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