[GSBN] Fwd: Decrement factor of SB walls
forum at lamaisonenpaille.com
forum at lamaisonenpaille.com
Wed Dec 7 10:57:51 UTC 2011
Hello,
The woodfiber panels that are between the vented airspace and the straw
are open to watervapour but close the wall to air movement. I feel there
is no more outside air comming through these walls then if they were
plasterd on both sides. These boards are also structural and present a
certain fire resistance. The internal convection as mentioned earlier on
this list by David Eisenberg and others is indeed a concern and
personally I have adopted the idea of buttering the bales with plaster
before pushing the bales against the boards from the inside. The plaster
needs to be quite sticky; if not it falls off when pushing the bales in
place.
The reason I like this method is that it allows us to :
- get a better rain protection than plaster can
- to have an effective way of ataching cladding (which was the starting
point of my reflection on how the wall 'should' be made).
One of the things that bugs me with plaster behind a rainscreen is that
I either find it hard to attach the cladding or I have wood comming
through the plaster and thus not an air and water barrier. If any of you
have cost a effective and well preforming method that allows a
continuous plaster barrier behind cladding I'm keen to see it.
- to easily respect (here in France) the post and beam building regulation
- to close the envelope rain before placing the bales
- to have a building method that makes it easy for regular builders to
adopt SB
Unfortunately the authors of the book Jorge mentioned, who indeed have a
very good reputation, don't cite the source of numbers given. To my
knowledge there has been no thermal testing in France on whole SB wall
assemblies. I therefor fear that the numbers given are calculations,
rather than observations, probably based on the assumption that the
R-value for a SB wall is the same whether plastered or not. I would be
very pleased to read thermal test results from 'dry' SB construction
methods on whole assemblies but have not yet come across any.
Have a peacefull day,
Andre
Le 06/12/2011 22:53, Danny Buck a écrit :
> I side with Dereck in general and in particular on impact of the
> thermal characteristics with no exterior render. There is the
> potential for air infiltration through the joints between bales and
> accompanying convective currents that can be set up with the delta T
> across the thickness of the bale. I believe a significant component of
> a bale wall's thermal performance comes from the interstices being
> closed off from the outside atmosphere on both sides of the wall.
> I do not remember the particulars, but as I recall, there have been
> tests done on bale walls where the R-value was dramatically lower than
> in other tests and one of the differences was the lack of render on
> both sides of the wall.
> Thanks,
> Danny Buck
>
> ----- Original Message -----
> *From:* Van Krieken <mailto:vankrieken at gmail.com>
> *To:* Global Straw Building Network
> <mailto:GSBN at sustainablesources.com>
> *Sent:* Tuesday, December 06, 2011 9:21 AM
> *Subject:* Re: [GSBN] Fwd: Decrement factor of SB walls
>
> Yes, Dereck, you're right. In this example there is no exterior
> plaster/render. Instead, there is a 16mm rainscreen panel (could
> be fiberwood).
> I attach here a picture of the example presented in the book.
>
> Thanks
>
> Jorge VK
>
>
>
>
>
>
> On Tue, Dec 6, 2011 at 2:34 PM, Derek Roff <derek at unm.edu
> <mailto:derek at unm.edu>> wrote:
>
> Thank you, Jorge, for greater details on the French research.
> It appears to me that the construction describes a wall with
> earthen plaster/render on the inside, and no plaster/render on
> the outside. Is this correct? If so, the lack of an exterior
> plaster/render layer would have a significant effect on the
> thermal characteristics, I would think. As well as fire
> resistance, structural rigidity, moisture buffering, and
> perhaps a bit of insect and rodent deterrence. I know that
> some people build this way, but it seems imprudent to me.
> Have I misunderstood the nature of the wall that Jean-Pierre
> Oliva and Samuel Courgey are describing/testing?
>
> Thank you,
> Derelict
> Derek Roff
> derek at unm.edu <mailto:derek at unm.edu>
>
> On Dec 6, 2011, at 5:52 AM, Van Krieken wrote:
> John,
>
> As I wrote before, the best source of information (I have)
> about this issue it is the book writen by Jean-Pierre Oliva
> and Samuel Courgey ( L'Isolation Thermique Ecologique).
>
> Jean-Pierre Oliva is perhaps the best known french bio
> climatic architect, and since many years a great enthusiast of
> straw bale building. His books (also La Architecture
> Bioclimatique) can be found at Amazon.
>
> Unfortunately, this book is only in FRENCH. I am sorry if my
> translation was not well done, so I include here the original
> text in french.
>
> Citing their book, page 175, concerning a wall with wood
> structure and straw bales with medium density (80 to 110
> Kg/m3, strawbale section 34x46cm. Vented façade (or rainscreen
> claddind) in exterior, and interior with clay render.
>
> Note.: I attach to this discussion a paper wrote by Jim
> Carfrae, attached to this forum last January, 22, where you
> may have more information about the benefits on using of a
> rainscreen clading in a straw bale building, specially on
> humid climates.
>
> The rainscreen cladding is included in the calculation of
> JeanPierre Oliva for this next example:
>
> Wall:
>
> 1. Bardage bois (2cm)
> 2. lattes support et contre-latte (6cm minimum)
> 3. Panneaux pare-plui contreventans (16mm)
> 4. Poteaux bois massif (4x20 tous les 60cm)
> 5. Liteau de maintien des bottes (toutes les 2 bottes)
> 6. Botte de paille posé sur champ (36cm)
> 7. enduit terre (30mm)
>
> Caracteristiques Thermiques et environnementales:
>
> Coeficient de déperdition thermique U (W/m2K) / R (m2K/W)
> .................................. 0,13 / 7,76
> Pertes dues aux points thermiques
> intégrés....................................................................
> 4%
> Capacité thermique intérieure
> quotidiennekWh/m2K)..................................................
> 15 (forte)
> Capacité thermique intérieure séquentielle
> ....................................................................25
> (moyenne)
> Déphasage (heure) / Atténuation du flux de chaleur
> (%)..............................................16h / 13%
> Epaisseur supplementaire pour atteindre le niveau
> "passif"....................................... 0
> Bilan "CO2" du m2 de
> paroi.............................................................................................
> -83 kg CO2 eq
> Bilan "energie grise" du m2 de
> paroi..............................................................................
> 62 kWh
>
>
> Translation (?):
>
> 1. Thermal loss U (W/m2K) / R (m2K/W)
> .................................. 0,13 / 7,76
> 2. Losses due to thermal
> bridges............................................... 4%
> 3. Dailyindoorheat capacity
> (kWh/m2K)................................ 15 (strong)
> 4. Sequential indoor heat capacity
> (kWh/m2K).......................25 (medium)
> 5. Phase shift (hour) / mitigationof the heat flux
> (%)............... 16h / 13%
>
>
>
> All the best
>
> Jorge VK
>
>
>
> ---------- Forwarded message ----------
> From: *John Swearingen* <jswearingen at skillful-means.com
> <mailto:jswearingen at skillful-means.com>>
> Date: Tue, Nov 29, 2011 at 1:35 AM
> Subject: Re: [GSBN] Decrement factor of SB walls
> To: Global Straw Building Network <GSBN at sustainablesources.com
> <mailto:GSBN at sustainablesources.com>>
>
>
> This is very interesting, and fortunately in English.
> Unfortunately, I don't really know what it means. Can you
> explain more?
>
> * U-value I know.
> * Thermal bridges to nowhere, I know, but what is a
> "vented facade" (above).
> * What are daily indoor heat capacities and sequential head
> capacities, and what does "strong" and "medium" mean?
> * Phase shift mitigation?
>
> Thanks!
>
> On Mon, Nov 28, 2011 at 3:40 PM, Van Krieken
> <vankrieken at gmail.com <mailto:vankrieken at gmail.com>> wrote:
>
> Hi
>
> The best source of information about this issue (and many
> others concerning insulation, thermal mass, etc) it is the
> book writen by Jean-Pierre Oliva and Samuel Courgey (
> L'Isolation Thermique Ecologique).
>
> Citing their book, page 175, concerning a wall with wood
> structure and straw bales with medium density (80 to 110
> Kg/m3, strawbale section 34x46cm. Vented façade in
> exterior, and interior with clay render.
>
>
> Thermal loss U (W/m2K) / R (m2K/W)
> .................................. 0,13 / 7,76
> Losses due to thermal
> bridges............................................... 4%
> Dailyindoorheat capacity
> (kWh/m2K)................................ 15 (strong)
> Sequential indoor heat capacity
> (kWh/m2K).......................25 (medium)
> Phase shift (hour) / mitigationof the heat flux
> (%)............... 16h / 13%
>
> Unfortunately, this book is only in English. Jean-Pierre
> Oliva, is one of the best known french bio climatic
> architects, and since many years a great enthusiast of
> straw bale building. His books (also La Architectire
> Bioclimatique) can be found at Amazon.
>
>
> All the best
>
> Jorge VK
> Portugal
>
>
>
>
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