[GSBN] Mechanized Cob Workshop: Using an excavator to mix and applycob

Mon Sep 30 21:35:22 UTC 2013

Thanks again Feile,

I originally wrote you off the list but it seemed that these issues you
bring up may also find a strong response on GSBN.  I believe you may have
assumed we were on the list anyway.

As as a civil engineer conducting mostly structural work, thermal qualities
are not my forte.  Although Massey Burke a designer/builder I have been
working with has recently put a cob building through California's somewhat
stringent Title 24 energy requirements matrix and it luckily did not come
out with a big fat X.  In fact, California has a Heavy Mass Wall option in
our matrix.  Massey knows much more about the process than I do so I've
copied here here to continue the conversation.

Thanks,
~Anthony

Anthony Dente, PE, LEED AP
Kevin Donahue Structural Engineers
Berkeley, CA
814.502.6001

On Mon, Sep 30, 2013 at 4:02 AM, Feile at Mud and Wood <feile at mudandwood.com
> wrote:

> **
> Hello again Anthony,
>
> Cheers re: the website.
>
> Regarding building regulation compliance, we have advantages and
> disadvantages in Ireland.
>
> We don't have to worry about seismic loading at all. As for issues
> regarding structural documentation for cob buildings, while we have no
> written codes, we have 1000s of centuries old cob buildings dotted around
> the country which are living proof that this method of construction is
> durable and structurally sound. However, sometimes you get a building
> control officer (or a mortgage provider) who wants the agrement cert or the
> accredited laboratory certificate for the material - which is obviously
> impossible and is something I'm trying to challenge at the moment.
>
> I'm sure our system is similar to a lot of countries, where the building
> regulation itself is only two or three sentences long, but the accompanying
> technical guidance document is a detailed prescription for how to achieve
> that regulation. If you follow the guidance word for word, you are deemed
> to have met the regulation. If you take a different path, the onus is on
> you to prove that you are meeting the regulation and if you have a
> close-minded building control officer or mortgage lender, that can be
> extremely difficult. It puts clients off, as it obviously takes more time
> and money to convince unyielding officials of methods and materials which
> do not neatly fit inside the box and there is no guarantee of a positive
> outcome.
>
> There are ways around some of the challenges, e.g. fire - materials in
> certain locations should have an organic content of 1% or less. Cob has
> approx. 15%. But there have been enough fires in cob buildings to prove
> that cob walls are fire-resistant.
>
> My biggest bug bear is the energy efficiency regulations - all about
> reducing carbon footprints - but which completely ignore embodied energy.
> So you can build the most energy efficient house on the planet and get an
> A1 rating, but it is built out of every toxic, carbon-loaded material
> going. I know Jim Carfrae (is he on this list?) has done work comparing the
> carbon footprint of a "regular" passivehaus house compared with a
> straw-bale passivehaus house and found that both achieve the same energy
> efficiency but that the embodied energy of the regular passivehaus was
> equivalent to 40% of the operational energy over 60 years (I think), while
> the embodied energy of the straw bale house was only equivalent to 5%.
>
> There is a lot of anecdotal evidence about the warmth of cob buildings
> compared to their calculated u-value expectation. U-values are an
> inadequate way to measure the thermal properties of monlithic
> materials with high thermal mass coupled with high thermal inertia. The
> regulations take no account of humidity balancing and as RH has a bigger
> infleunce on the perception of comfort than air temperature, it could be
> argued that materials which promote even, optimum RH levels can provide
> thermal comfort at lower temperatures. We have a huge problem with the
> performance gap in Ireland - the actual measured performance of the built
> building compared to its calculated performance. The very few tests which
> have been carrried out on (historic) cob buildings in Scotland have shown
> that they perform up to 150% (and more) better than expected. Whereas tests
> on conventionally built buildings in Ireland and the UK have provided
> results 150% and even 200% worse than expected.
>
> Our energy efficiency regulations now include software calculations in the
> actual regulation itself (not in the technical guidance document). A small
> area of wall is allowed to fall outside the current u-value of 0.21 W/m2K,
> as low as 0.6 W/m2K. Cob walls can achieve this. But what do you do with
> the rest of the wall area? I contend that cob walls need nothing like the
> level of insulation that the calculations state. I believe that it is not
> sustainable to slap on a load of unnecessary insulation material just to
> tick the box in a computer equation which cannot adequately deal with the
> material involved. Besides, the wall construction ends up getting so deep,
> that it stops being a sensible way to build. Also some research has been
> carried out in France which showed that the addition of insulation to
> a rammed earth wall ended up increasing the overall moisture content of the
> wall, thereby decreasing the thermal performance of the rammed earth. There
> may been a net gain in overall thermal performance, but unfortunately, this
> wasn't measured - they were just concerned with the moisture levels in the
> earth construction. Needless to say, increased moisture levels also brought
> the wall closer to its danger point from a structural collapse point of
> view.
>
> In England and Scotland, the approach is to super-insulate other parts of
> the building that can be super-insulated and to leave the cob walls as
> traditional cob walls. We took that approach with our own house here (which
> was built before the regulations got tighter- but we still super-insulated
> a lot of the envelope). Nowadays the software throws up a big fat X
> beside any cob walls. Some building control officers may accept that the
> whole house performance is meeting the requirements. But some may not and
> if there is an element that clearly does not comply, this is their reason
> to refuse it.
>
> On this note, I would love to be pointed towards any studies on the
> following:
>
>    - Humidity buffering and balancing properties of earth, its effect on
>    internal relative humidity and perception of thermal comfort.
>    - measured thermal performance of contemporary earth-constructed homes
>    - other methods for measuring the thermal properties of materials -
>    any kind of equation, etc, which could be added to u-values to modify them
>    to take account of what is really happening in the real world (with time
>    lag, humidity regulations, etc).
>    - the ability of earth to bind toxins.
>    - I'm aware of the NZ earth-building codes and the UK Code of Practice
>    for Rammed Earth. Please let me know what else is out there.
>
> I think the points about humidity-buffering and toxin-binding are
> particularly exciting. If the fabric of the building itself can remove
> excess moisture and toxins from the internal atmosphere, then there could
> be potential for reducing ventilation requirements. Even controlled
> ventilation equates with either heat loss or energy needed for heat
> recovery.
>
> As for the reinforcement properties of straw, the last email I posted
> refers to testing done in Bath and Plymouth Universities and Cra-terre
> which might be able to help.
>
>
> Regards
>
>
>
> *Féile Butler*
>
> *MRIAI B.Arch Dip. Arch Conservation Grade III*
>
> *Mud and Wood*
>
> ***Grange Beg, Skreen, **Co. Sligo, Ireland*
>
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> ********
>
> ******
>
> ******
>
> ******
>
> ***T:  +353 (0) 71 930 0488 ***
>
> *****M: +353 (0) 86 806 8382*****
>
> *******E : ****feile at mudandwood.com*******
>
> *****W: www.mudandwood.com*****
>
>
>
>
>
>
> ----- Original Message -----
>
> *From:* Anthony Dente <dente.a at gmail.com>
> *To:* Feile at Mud and Wood <feile at mudandwood.com>
> *Sent:* Friday, September 27, 2013 10:05 PM
> *Subject:* Re: [GSBN] Mechanized Cob Workshop: Using an excavator to mix
> and applycob
>
> Hi Feile,
>
> Nice website.  It looks like you are doing some great things over in
> Ireland.  Your statement "We have a big emphasis on building regulation
> compliance" intrigued me.  I'm not well versed in Ireland building codes
> and my limited knowledge of the region has me believing your seismic loads
> are small but I am very interested in hearing about how you deal with wind
> loading when communicating with your building department.
>
> I'm a professional engineer in California and I've been working on the
> design of of number of cob structures in our highly seismic region
> recently.  My largest struggles are just a lack
> of structural documentation.  As well as the terminology battle of weather
> straw can even be considered as "reinforcement" in our country.
>
> I just wanted to write to see if you had anything interesting to share on
> that matter.  I am happy to share our reports as well after we reach a
> conclusion with our building departments if that would possibly help with
> any of your projects.
>
> Thanks and take care,
> ~Anthony
>
>  Anthony Dente, PE, LEED AP
> Kevin Donahue Structural Engineers
> Berkeley, CA
> 814.502.6001
>
>
> On Fri, Sep 27, 2013 at 1:38 AM, Feile at Mud and Wood <feile at mudandwood
> .com> wrote:
>
>> **
>> Hi Mischa
>>
>> Best of luck with the cob course.
>>
>> Just to say we have been running 8-day courses for the past 2 years in
>> Ireland teaching digger mixing cob and using forms to speed up the process.
>> The course is very much aimed at building larger cob structures as family
>> homes, etc. We have a big emphasis on building regulation compliance (which
>> can present its own challenges!). You can click here for a link to the 2012
>> course <http://www.mudandwood.com/news-and-articles.html#courses> and 2013
>> course <http://www.mudandwood.com/news-and-articles.html#eightday>.
>>
>> We always start with foot-mixing for a day as it is an invaluable
>> introduction to getting to know the material. It also always blows our
>> students minds how quickly the process goes once you move from foot- to
>> digger-mixing. It really makes them appreciate the value of using the
>> digger.
>>
>> Hope you get plenty of people signing up. And if you know anyone who like
>> to learn about it on this side of the pond, put them in touch with us!
>>
>>
>> Kind Regards
>>
>>
>>  *Féile Butler*
>>
>> *MRIAI B.Arch Dip. Arch Conservation Grade III*
>>
>> *Mud and Wood*
>>
>> ***Grange Beg, Skreen, **Co. Sligo, Ireland*
>>
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>> ********
>>
>> ******
>>
>> ******
>>
>> ***T:  +353 (0) 71 930 0488 ***
>>
>> *****M: +353 (0) 86 806 8382*****
>>
>> *******E : ****feile at mudandwood.com*******
>>
>> *****W: www.mudandwood.com*****
>>
>>
>>
>>
>>
>> ----- Original Message -----
>> *From:* Misha Rauchwerger <misha.rauchwerger at gmail.com>
>> *To:* Global Straw Building Network <GSBN at sustainablesources.com>
>> *Sent:* Thursday, September 26, 2013 7:05 AM
>> *Subject:* [GSBN] Mechanized Cob Workshop: Using an excavator to mix and
>> applycob
>>
>>   Hi Everyone,
>>
>> I thought there may be folks out there on this list serve either
>> interested in taking this possibly one-of-a-kind cob workshop, or you may
>> have networks, email lists, etc. to get the word out to interested
>> parties.  I would very much appreciate the assistance.  I think it may be a
>> different crowd than is typically drawn to cob workshops, so appealing to
>> the professional side of natural building seems like it may have a better
>> chance of reaching interested parties.
>>
>> Thanks,
>> Misha Rauchwerger
>> Builtinbliss.com
>>
>>  ------------------------------
>>
>> _______________________________________________
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>> GSBN at sustainablesources.com
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>>
>>
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>>
>
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