[GSBN] Fwd: Decrement factor of SB walls

Wed Dec 7 10:05:53 UTC 2011

Hi Bohdan
Christian et al (Oak Ridge Lab 1998) tested a whole wall but there was only plasterboard on the interior. Andersen 2004 tested a bale wall rendered both sides. The tests are expensive and flawed. And basing heat loss calculations on conduction (r values or u-values) is wholly inadequate because most heat loss is lost through convection and then there are all the other factors such as time lag (thick straw bale walls), thermal bridging, surface emissivity, thermal mass (render), airtightness (render), use of rain screens and all the other factors in a building such as windows, floor and ceilings. (see my thesis - about page 35 onwards 
http://www.homegrownhome.co.uk/pdfs/Energyassessmentofastrawbalebuilding.pdf )

A well built straw bale building will perform much better than the theoretical heat flow calculations (using r or u values) would suggest because of all these other factors.  Manufacturers of building materials have the resources to keep doing the flawed tests to get a result that makes their product have as high a r or u value as possible because this is what our flawed building regulations require. They are not concerned about how that material will perform in a real life situation.  

Sorry - preaching to the converted!
Carol

-----Original Message-----
From: Bohdan Dorniak <bdco at adam.com.au>
To: 'Global Straw Building Network' <GSBN at sustainablesources.com>
Sent: Tue, 6 Dec 2011 22:28
Subject: Re: [GSBN] Fwd: Decrement factor of SB walls

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

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