[GSBN] Fwd: Decrement factor of SB walls
David Arkin, AIA
david at arkintilt.com
Wed Dec 7 13:19:42 UTC 2011
Hi All:
I located our report from the Real Goods project I mentioned a couple weeks back. Attached, with its appendices. It is based on post-occupancy performance data done by students at the University of California - Berkeley.
Jump to p. 4 for the straw-bale discussion, and also Appendix I. I note that the students needed a guess at an assumed R value in order to generate a predicted set of core temperatures, and then used actual data to somewhat confirm it. That does not fully justify that the walls have an actual Rus-value of 65 (Rsi-11.44) [Uus-value of .015 (Usi-0.087)] but I do suspect that it's somewhere approaching that.
Again, these walls have 23" (584mm) 3-string rice straw bales, laid flat, with ±3" (76mm) of PISE (earth-cement) on the interior and ±4" (102mm) on the exterior.
Permit me to be the first to say that this is not the most scientific study.
If I recall correctly, when the State of California tested bale a bale wall panel for R-Value, the sample wall was still wet, and tested to Rus-value of 33 (Rsi-5.81). Here I suspect the actual value is higher, and probably would've been had the plaster and bales been more dry. But as a result the California Energy Commission assigned an assumed Rus-value of 30 (Rsi-5.28) for bales laid both flat or on edge. That's the value we still use today.
So, while perhaps not truly tested, it is safe to say bale walls have thermal performance values that fall somewhere between 'impressive' and 'stunning'.
Cheers,
David
ps: On the question of an exterior render—or not—behind a rain screen, for a lodge in Alaska we applied a thin coat of earth-cement plaster (sandy site soils mixed with cement), more due to concerns about keeping critters out than about air movement. There's a 1" (25mm) gap between the plaster and a loosely fitted log cull rain screen. While air movement within bales is very dependent upon the density, I have to agree with Danny's hypothesis that limiting of air movement with an exterior render greatly improves r-value.
On Dec 6, 2011, at 2:26 PM, Bohdan Dorniak wrote:
> Are there any tests on the R-value of rendered strawbales?
> In my research (over 12 years as an architect of strawbale houses and other buildings) I’ve never been able to find a true tested value.
> Would appreciate any help here.
> Bohdan Dorniak
> AUSBALE
>
> From: GSBN-bounces at sustainablesources.com [mailto:GSBN-bounces at sustainablesources.com] On Behalf Of Danny Buck
> Sent: Wednesday, 7 December 2011 8:24 AM
> To: Global Straw Building Network
> Subject: Re: [GSBN] Fwd: Decrement factor of SB walls
>
> 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
> To: Global Straw Building Network
> 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> 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
>
> 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. Daily indoor heat capacity (kWh/m2K)................................ 15 (strong)
> 4. Sequential indoor heat capacity (kWh/m2K).......................25 (medium)
> 5. Phase shift (hour) / mitigation of the heat flux (%)............... 16h / 13%
>
>
>
> All the best
>
> Jorge VK
>
>
>
> ---------- Forwarded message ----------
> From: John Swearingen <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>
>
>
> 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> 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%
> Daily indoor heat capacity (kWh/m2K)................................ 15 (strong)
> Sequential indoor heat capacity (kWh/m2K).......................25 (medium)
> Phase shift (hour) / mitigation of 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
>
>
* * * * *
Arkin Tilt Architects
Ecological Planning & Design
CoolCalifornia.org
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David Arkin, AIA, Architect
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1101 8th St. #180, Berkeley, CA 94710
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www.arkintilt.com
"There is no way to peace. Peace is the way."
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