[GSBN] SB wall height limit (was Clay plaster language for IBC)

[Derek Roff]

Thank you for your response, Martin,

I am glad to hear that the proposed maximum height to width ratio is being increased, at least in some cases.  It would be interesting to hear from David or Matts about the 5.6 to 1 ratio in the 1995 Arizona code.  This would not have reflected some of the historical Nebraska SB structures, which they both had studied.  Let me be clear, that I don't consider the multi-decade survival of a handful of taller-walled strawbale buildings to be proof that these designs are safe enough and reliable enough for a building code.  They are interesting data, but far from proof.  I put more faith in the university testing, but perhaps those tests aren't convincing to some of the engineers involved in the code proposal that you are working on.  

I'm guessing from your words in the second paragraph about mesh and pinning, that the compression straps used by many builders would not be sufficient.  If so, it sounds like the proposed code will still ban two-string bales on edge, as practiced by some of our more experienced builders, that is, 8'-9' tall walls without mesh or pinning.  Internal pinning, as commonly practiced, and endorsed in the early writings of the SB revival, is of dubious structural value.  I'm surprised that it has the endorsement of the engineers involved with this proposal.  But maybe the internal pinning that you mention has different requirements.  I would be interested is seeing the specifications for the endorsed pinning options.  

Will there be any distinction in the code proposal between building in seismically active zones, such as the Pacific Coast, compared to more seismically tranquil locations?  

Thanks again,

Derelict

Derek Roff
derek at unm.edu


On Jan 25, 2012, at 6:10 PM, martin hammer wrote:

> Thanks Derek,
> 
> Delayed reply on this.  I was aware of this problem, which we addressed during a meeting of our “structural task force” Sunday.  The proposed ratio will be increased to 7:1 or 8:1 “of stacked bale height to bale width between restraints”.  If an 8:1 ratio is proposed there will probably be a height limit of 12 feet.  Taller walls could be built, but they would need intermediate restraint or would need to show an engineered design demonstrating they adequately resist buckling (under any imposed vertical load or design out-of-plane horizontal loads).
> 
> This height to width limit is for walls with mesh reinforced plasters or external or internal pinning, or out-of-plane restraint by structural framing (with sufficient attachment).  The height to width limit for walls without any of those means of resisting out-of-plane loads will be lower (still being determined).
>   
> The historical height to width limit for load-bearing walls has been 5.6 to 1 (going back to the 1995 Arizona code written by Matts and David Eisenberg).  For 3-string bales laid flat this is 10’-8” (8 courses).  For 2-string laid flat it is 8’-4” (7 courses).  2-string laid flat doesn’t really pencil out, at 6’-6” or 4.25 courses.
> 
> I anticipate flak during the review process of anything over 5.6 to 1.  I already heard it during the IGCC process, even at 6:1.  Kevin Donahue (structural engineer in CA) is writing a rational analysis to defend the increase based on out-of-plane testing and fundamental structural mechanics.
> 
> Another point of reference by the way, is that in the IBC, unreinforced adobe has a height to width limit of 10:1 (with a minimum exterior wall thickness of 10”).
> 
> I may be saying too much here and it’s a little more complex than what I describe, but I hope this answer is sufficient.
> 
> Martin
> 
> 
> 
> On 1/18/12 9:12 AM, "Derek Roff" <derek at unm.edu> wrote:
> 
>> Hi, Martin,
>> 
>> I appreciate your continued work on so many levels for the promotion and support of more sustainable building practices, procedures, and modalities.  I'd like to ask again, about an element of the proposed code, which seems to contradict some of the goals that we share on this list.  Will your next code proposal continue to effectively ban stacking bales on edge, or using smaller-dimension bales, such as those you used in Pakistan and Haiti?  The provision that I am referring to limits the height of a wall to six times its thickness.  This means a maximum ceiling height of 6', if one is using the 12"x12" bales like you used in Haiti, and 7', if you stack the common American two-string bales on edge.  Such low ceilings are likely to violate other code requirements, and few of us want to be forced to build a portion of our wall height out of another material.  These building options are used on some projects by many of our most experienced and innovative builders.  The structural strength taller walls is documented in multiple university tests on several continents, and its reliability in practice is shown in many of the oldest historical strawbale buildings.  I would be very sad if a forthcoming code contains a provision that makes these building options illegal.  
>> 
>> I think we would all like any code proposals to be a good as possible, and of course there will be differences of opinion on just what "good" means on certain points.  However, to support a code provision that bans a widespread strawbale building option is something that I feel requires extensive discussion.  I'm hoping that the provision has been removed from the code proposal, but if it remains, are you willing to discuss it?  
>> 
>> Thanks,
>> Derelict
>> 
>> Derek Roff
>> derek at unm.edu
>> 
>> 
>> On Jan 17, 2012, at 1:10 AM, martin hammer wrote:
>> 
>>> Clay plaster language for IBC 
>>> Hello all,
>>> 
>>> I proposed a Strawbale Construction section for the International Building Code (IBC) on January 3.  I have been allowed by the International Code Council to make adjustments until January 25, before the proposal becomes public.  
>>> 
>>> I have continued refining the language with a structural task force (that has worked on this since October) as well as obtaining input from the Structural Engineers Association of California, a long time opponent strawbale construction in building codes.  They are now pulling on the same end of the rope.  Dan Smith and John Swearingen of this list have helped adjust the non-structural language.  I also received input from Andy Mueller of this list for a renewed Northeastern US perspective.
>>> 
>>> One area of this “code” I feel is under-developed is the part on Clay Plaster (and secondarily Soil-Cement).  An entire section is devoted to “Finishes”, which is mostly about plasters.  This includes clay, soil-cement, lime, cement-lime, cement, and gypsum plasters.  For the last four plaster types I reference long-standing sections of the International Building Code or ASTM Standards (with a some adjustments for use of these plasters on strawbale walls).  Wherever possible (and wherever not inappropriate for strawbale) it is best for this proposed strawbale section to be in sync with the IBC and its referenced standards.
>>> 
>>> However clay plaster (and soil-cement plaster) is new territory for the IBC.  New language must be forged here, but it needs to be code-appropriate as follows:
>>> 
>>> Minimum practice, not best practice.
>>> Enforceable
>>> Says what shall be or shall not be done, not what should or may be done.
>>> 
>>> Would anyone from this list (with good clay plaster experience) like to be part of a mini task force on this issue?  If people let me know by end of Wednesday January 18, the individual or small group (no more than 3?) would have through Monday January 23 to propose language.  I could send you what I have currently off-list or you could choose to be blind to it.  Looking at existing language regarding plasters in the IBC or in ASTM standards (if you have access to these), is not mandatory but might be useful.
>>> 
>>> Is anyone willing and able?
>>> 
>>> Thanks.
>>> 
>>> Martin Hammer




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