[GSBN] Pedagogical and in-depth explanation of diffusion-open exterior wall system

[Rikki Nitzkin]

Thanks for the link, Chris. 

The building science part of the article is ok, but I was shocked at some of the statements in the introduction to the article. I hope when you use the information, you quote it instead of sending the link.

Some of the claims in it, we now know are not true and they mention as commonplace techniques which are now rarely or ever used (at least in Europe). I did notice that the article is almost 10 years old...

The classic and time-proven strawbale wall assembly consists of strawbales laid flat with a 1 to 1.5 inches (25 to 38 mm) thick metal mesh reinforced cement and/or lime stucco skin applied directly to each face. 

I don’t know anyone in Europe who uses neither metal mesh nor cement stucco. There is absolutely no need for it, as long as clay and/or lime are available locally. The mesh reinforcement is not necessary with lime or clay plasters, as long as the first (primer) coat is worked into the wall well. We sometimes add a plastic or natural mesh in the finish layer to help avoid cracks, especially if there is no fibre reinforcement in the finish coat.

Are people still using these techniques in the US and Canada? Why?

The reinforced skins take almost all of the load since these are the stiffest and strongest materials in the system.

I understand that although it is true that the plaster skins can double the load bearing capacity of the walls, this statement leads people to believe that that the straw cannot carry loads itself. That is simply not true. Well compressed bales can carry quite a large load, although the protection and extra strength the plaster gives is welcome. With statements like that, you would think that a house with out plaster is unstable (especially load-bearing houses). If the house is unstable, it is not well built or is made with inferior quality straw bales. There is no rush to get that plaster on!

I am sure Barbara would agree with me here!

Naturally yours, 

Rikki

Rikki Nitzkin
Straw Building and Earthen Plasters: training, consulting and building
www.tallerconco.org
https://www.facebook.com/TallerConCo
tallerconco at gmail.com
+34 657 335 162




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> El 22 ago 2018, a las 2:14, Chris Magwood <chris at endeavourcentre.org> escribió:
> 
> Hi Lars,
> 
> My go-to for building officials and others wanting to understand this is John Straube's document on the BuildingScience.com web site: https://buildingscience.com/documents/digests/bsd-112-building-science-for-strawbale-buildings
> 
> Chris
> 
> On 2018-08-20 9:06 AM, Lars Keller wrote:
>> Dear colleagues,
>> In Denmark non-diffusion-open exterior walls are very common.
>> I am communicating with a Phd-student at the Danish Building Research Institute who has a background of sustainable projects and who is keen to put an effort into understanding how it is that diffusion-open exterior wall systems actually work.
>> This might be obvious to many of us - we have seen the evidence.
>> But the learned opinion in Denmark says that diffusion-open exterior walls generally do not work.
>> 
>> So, I am after resources. Homepages. Book-titles. Research. That explains how and why.
>> ?
>> 
>> Best, Lars
>> -- 
>> -- 
>> Small Planet
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>> Kontakt-info
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>> 
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>> 
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> -- 
> Chris Magwood
> Director, Endeavour Centre
> 
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