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 Post subject: Material data for straw bale walls
PostPosted: Mon Aug 08, 2011 5:24 am -1100 
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We repeatedly receive inquiries about material data for straw bales which are an increasingly popular building material. IBP has participated in a research project investigating various performance aspects of straw bale walls, which comprised collecting material data, performing simulations for a variety a constructions and comparison of measurements on two weather-exposed straw bale walls with simulations.

The material data used in these simulations have not been included in WUFI's material database because straw bales, being a "natural" material, may differ greatly in their hygrothermal properties (depending on type of straw, alignment of straws, degree of compression, possible chemical treatments etc).

Due to popular demand, we list below some material data for straw bales and clay rendering, excerpted from the project report "Grundlagen zur bauaufsichtlichen Anerkennung der Strohballenbauweise- Weiterentwicklung der lasttragenden Konstruktionsart und Optimierung der bauphysikalischen Performance.

These may be useful as a rough guide or as a starting point for your investigations. Because of the strong variations to be expected for products coming from different regions or manufactured by different processes, we can not guarantee that these data are also applicable to the materials used in your project. The data given below reflect some of the possible variation.

Refer to the report for the individual sources of the data and details on the various measurement procedures.

You can download a WUFI project file which contains material data for straw bales and clay rendering that have been used for simulations of straw bale walls. However, given the strong variation of material data evident from the lists of data given below, this file may be applicable to your straw bale walls, or it may not.

Straw Bales:

Density measurements on rye straw bales used for investigations on mechanical stability:
p. 43, measured by Hochschule Magdeburg- Stendal
Code:
mean bulk density of 36 samples: 130.12 +- 8.73 kg/m³
(Variation of these samples is
larger than that of typical
bales used for construction).


Density of high-density wheat straw bales:
Measured by ZUB

Code:
Dry density, computed (p. 87) from the measured moist mass and
the measured moisture content for six samples:

#1:  76.96 kg/m³
#2:  69.71 kg/m³
#3:  71.69 kg/m³
#4: 117.73 kg/m³
#5: 111.08 kg/m³
#6: 107.41 kg/m³
(p. 100)



Material data for straw
as used by Österreicherisches Ökologieinstitut für
angewandte Umweltforschung (and related by ZUB, p. 126):

Code:
Straw: bulk density                rho    = 100 kg/m³
       porosity                    psi    = 0.9
       heat capacity               cp     = 2000 J/(kg K)
       thermal conductivity        lambda = 0.045 W/(m K)
       diffusion resistance factor mu     = 1.3


The same data have been used by ZUB for the present report (p. 138).

The moisture storage function has been derived by re-scaling the
moisture storage function of wood for the bulk density of the straw.
See report p. 139, Fig. 5-1 for a plot

Liquid transport (both suction and redistribution) has been ignored
"because of the large distances between the straws".


Thermal conductivity
Design value determined for a straw bale sample with
Code:
bulk density 90 kg/m³: lambda_design = 0.045 W/(m K)

(related by ZUB, p. 128)


Material data of construction straw bales
measured by FIW (related by ZUB, p. 129)
Code:
 bulk density : 81 kg/m³
 lambda_10_dry:  0.067 W/(m K)
 mu:             2



Material data for straw
p. 283; measured by IBP and used in the simulations
for the present report:

Code:
bulk density of straw bale, air-dry: 90 kg/m³
sorption moisture content at 23°C, 65% RH: 1.21 vol.-%
sorption moisture content at 23°C, 80% RH: 1.80 vol.-%
sorption moisture content at 23°C, 93% RH: 2.51 vol.-%


Liquid transport in the straw bales is ignored because it
is expected to be too small to be relevant (p. 227).

Missing material data, such as thermal conductivity or
diffusion resistance factor have been taken from measurements
performed by FIW.

See fig. 10-22 (p. 270) for a comparison of the measured (black) and
simulated (blue) temperatures (top) and relative humidities (bottom)
for a straw bale wall with exterior lime rendering.



Measurements of heat conductivity:
Measurements by FIW.
(p. 299 and pp. 429 ff.)

Code:
Wheat straw, along the straws:
                      bulk density, dry: 105 kg/m³         ref.: p. 299 (Prüfbericht 2006), p. 433 & 442 (L1-06-134)
           bulk density at 23°C, 80% RH: 120 kg/m³               p. 299 (Prüfbericht 2006), p. 433 & 442 (L1-06-134)
 mass-specific moisture content u_23/80: 14.2%                                              p. 433 & 442 (L1-06-134)

                          lambda_10_dry: 0.0670 W/mK             p. 299 (Prüfbericht 2006), p. 433 & 442 (L1-06-134)
                      lambda_10_(23/80): 0.0800 W/mK             p. 299 (Prüfbericht 2006), p. 433 & 442 (L1-06-134)


Wheat straw, along the straws:
                      bulk density, dry: 116 kg/m³               p. 299 (Ergebnisse 2008)
           bulk density at 23°C, 80% RH: 133 kg/m³               p. 299 (Ergebnisse 2008)

                          lambda_10_dry: 0.065  W/mK             p. 299 (Ergebnisse 2008)
                      lambda_10_(23/80): 0.0715 W/mK             p. 299 (Ergebnisse 2008)


Wheat straw, across the straws:
                      bulk density, dry:   93 kg/m³              p. 299 (Prüfbericht 2006), p. 433 & 442 (L1-06-134)
           bulk density at 23°C, 80% RH:  105 kg/m³                                         p. 433 & 442 (L1-06-134)
 mass-specific moisture content u_23/80: 12.6%                                              p. 433 & 442 (L1-06-134)

                          lambda_10_dry: 0.0439 W/mK             p. 299 (Prüfbericht 2006), p. 433 & 442 (L1-06-134)
                      lambda_10_(23/80): 0.0472 W/mK             p. 299 (Prüfbericht 2006), p. 433 & 442 (L1-06-134)


Wheat straw, across the straws:
                      bulk density, dry:  97.2 kg/m³             p. 299 (Ergebnisse 2008)
           bulk density at 23°C, 80% RH: 109   kg/m³             p. 299 (Ergebnisse 2008)

                          lambda_10_dry: 0.0397 W/mK             p. 299 (Ergebnisse 2008)
                      lambda_10_(23/80): 0.0469 W/mK             p. 299 (Ergebnisse 2008)


Rye straw, along the straws:
                      bulk density, dry: 115 kg/m³               p. 299 (Prüfbericht 2006), p. 433 & 442 (L1-06-134)

                          lambda_10_dry: 0.0820 W/mK             p. 299 (Prüfbericht 2006), p. 433 & 442 (L1-06-134)


Rye straw, across the straws:
                      bulk density, dry:  93  kg/m³              p. 299 (Prüfbericht 2006), p. 433 & 442 (L1-06-134)
           bulk density at 23°C, 80% RH: 104  kg/m³                                         p. 433 & 442 (L1-06-134)
 mass-specific moisture content u_23/80: 11.8%                                              p. 433 & 442 (L1-06-134)

                          lambda_10_dry: 0.0422 W/mK             p. 299 (Prüfbericht 2006), p. 433 & 442 (L1-06-134)
                      lambda_10_(23/80): 0.0465 W/mK             p. 299 (Prüfbericht 2006), p. 433 & 442 (L1-06-134)


Heat conductivity of straw bales
(including some clay seaped into the bales),
determined from the measured U-value of a wall:
                          lambda_10_dry: 0.065 W/mK              p. 299, p. 453 (I1-08/06)


Wheat straw dried at 70°C; across the straws:
                       bulk density dry: 115 kg/m³               p. 434 & 443 (F.2-589/08)
                          lambda_10_dry: 0.0553 W/mK             p. 434 & 443 (F.2-589/08)


Wheat straw, along the straws
                       bulk density dry: 116 kg/m³               p. 299 (F.2-909/08, F.2-605/08), p. 437 & 438 & 446 (F.2-605/08,
                                                                                                    same sample as in F.2-909/08)
              bulk density at 23°C, 80%: 133 kg/m³               p. 299 (F.2-909/08, F.2-605/08), p. 435 & 444 (F.2-909/08)
 mass-specific moisture content u_23/80: 14.0%                                                    p. 435 & 444 (F.2-909/08)

                          lambda_10_dry: 0.0650 W/mK             p. 299 (F.2-909/08, F.2-605/08), p. 437 & 438 & 446 (F.2-605/08)
                      lambda_10_(23/80): 0.0715 W/mK             p. 299 (F.2-909/08, F.2-605/08), p. 435 & 444 (F.2-909/08)


Wheat straw, across the straws
                       bulk density dry:  97.2 kg/m³             p. 299 (F.2-714/08, F.2-916/08), p. 447 (F.2-714-08,
                                                                                                  same sample as in F.2-916/08) 
           bulk density at 23°C, 80% RH: 109   kg/m³             p. 299 (F.2-714/08, F.2-916/08), p. 436 & 445 (F.2-916/08)
 mass-specific moisture content u_23/80: 12.5 %                  p. 436 (F.2-916/08)

                          lambda_10_dry: 0.0397 W/mK             p. 299 (F.2-714/08, F.2-916/08), p. 447 (F.2-714-08)
                      lambda_10_(23/80): 0.0469 W/mK             p. 299 (F.2-714/08, F.2-916/08), p. 436 & 445 (F.2-916/08)




Interior Clay Rendering

Material data for clay rendering
as used by Österreicherisches Ökologieinstitut für
angewandte Umweltforschung (and related by ZUB, p. 126):

Code:
Clay rendering, (three coats): bulk density                rho    = 1514 kg/m³
                               porosity                    psi    = 0.4
                               heat capacity               cp     = 850 J/kgK
                               thermal conductivity        lambda = 0.7 W/mK
                               diffusion resistance factor mu     = 11.3

Clay rendering, mu=30:         bulk density                rho    = 1514 kg/m³
                               porosity                    psi    = 0.4
                               heat capacity               cp     = 850 J/kgK
                               thermal conductivity        lambda = 0.7 W/mK
                               diffusion resistance factor mu     = 30.0


The first set of data has also been used by ZUB for the present report (table 5-3, p. 139).
The moisture storage function has been derived from the sorption measurements
of IBP. See fig. 5-2, p. 139 for a plot of the moisture storage function.


Material data for clay rendering
Measured by IBP, related by ZUB (p. 129):

Code:
bulk density:   1514 kg/m³
true density:   2630 kg/m³

diffusion resistance factor (23°C, 0/50% RH): 11.3
diffusion resistance factor (23°C, 50/93% RH): 9.6

water absorption coefficient (A-value): 2.8 kg m^-2 h^-0.5

sorption moisture content at 23°C, 65% RH:  1.3  vol.-%
sorption moisture content at 23°C, 80% RH:  1.88 vol.-%
sorption moisture content at 23%C, 93% RH:  2.54 vol.-%
free saturation                          : 29.4  vol.-%

liquid transport coefficient, suction: Dw0: 2.0e-10 m²/s
                                       Dwf: 7.7e-8  m²/s

liquid transport coefficient, redist.: Dw0: 7.0e-10 m²/s
                                       Dwf: 8.0e-5  m²/s



Material data for interior clay rendering
Measured by IBP (p. 281).
Code:
bulk density, dry: 1798 kg/m³
true density     : 2707 kg/m³
porosity         : 34 vol.-%

diffusion resistance factor (23°C, 0/50% RH): 14.3
diffusion resistance factor (23°C, 50/93% RH): 8.7

water absorption coefficient (A-value) w1 : 4.6 kg m^-2 h^-0.5
water absorption coefficient (A-value) w24: 2.1 kg m^-2 h^-0.5

sorption moisture content at 23°C, 65% RH:  1.53 vol.-%
sorption moisture content at 23°C, 80% RH:  1.88 vol.-%
sorption moisture content at 23°C, 93% RH:  2.91 vol.-%
free saturation                          : 35.1  vol.-%

liquid transport coefficient, suction: Dw0: 2.0e-10 m²/s
                                       Dwf: 2.4e-8  m²/s

liquid transport coefficient, redist.: Dw0: 2.5e-9 m²/s
                                       Dwf: 5.0e-7 m²/s


Key words: straw bale walls, clay rendering, Stroh, Strohballen, Strohballenwand, Lehmputz


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 Post subject: Straw bales
PostPosted: Fri Aug 12, 2011 1:13 pm -1100 
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Joined: Fri Aug 12, 2011 12:55 pm -1100
Posts: 4
The latest version of WUFI 5.1.0.559 claims that it cannot open the strawbale file because it is an incompatible version.


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 Post subject:
PostPosted: Thu Mar 08, 2012 1:52 am -1100 
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Joined: Tue Mar 06, 2012 1:44 am -1100
Posts: 4
Hi Thomas,

I was wondering if theres an english version of the report, Ive seen sections of it quoted in english. Heres hoping!

Tuireann


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 Post subject: Re: Straw bales
PostPosted: Thu Mar 08, 2012 2:36 am -1100 
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WUFI SupportTeam IBP
WUFI SupportTeam IBP

Joined: Tue Jul 04, 2006 10:08 pm -1100
Posts: 695
Location: IBP Holzkirchen, the home of WUFI
lile001 wrote:
The latest version of WUFI 5.1.0.559 claims that it cannot open the strawbale file because it is an incompatible version.


Hello lile001,
the file is working in Wufi5, all versions. Do not open it directly, save it to your disc first. Sometimes it can happen, that the virus scanner from your computer wrecks the file.
Christian


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 Post subject: Re: Straw bales
PostPosted: Thu Mar 08, 2012 2:38 am -1100 
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WUFI SupportTeam IBP
WUFI SupportTeam IBP

Joined: Tue Jul 04, 2006 10:08 pm -1100
Posts: 695
Location: IBP Holzkirchen, the home of WUFI
Christian Bludau wrote:
lile001 wrote:
The latest version of WUFI 5.1.0.559 claims that it cannot open the strawbale file because it is an incompatible version.


Hello lile001,
the file is working in Wufi5, except light and ORNL version. Do not open it directly, save it to your disc first. Sometimes it can happen, that the virus scanner from your computer wrecks the file.
Christian


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 Post subject:
PostPosted: Mon Mar 12, 2012 8:23 pm -1100 
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Joined: Sun Aug 28, 2011 7:54 pm -1100
Posts: 10
Hello,
I would like to know if there is available any measured data about reed insulation mat?


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 Post subject:
PostPosted: Tue Mar 13, 2012 1:28 am -1100 
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WUFI Administrator
WUFI Administrator

Joined: Sun Jun 19, 2005 10:33 pm -1100
Posts: 225
Tuireann wrote:
I was wondering if theres an english version of the report, Ive seen sections of it quoted in english. Heres hoping!

Hi Tuireann,

I'm afraid I'm not aware of an English version or any plans to translate the report...

Regards,
Thomas


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 Post subject:
PostPosted: Tue Mar 13, 2012 1:46 am -1100 
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WUFI Administrator

Joined: Sun Jun 19, 2005 10:33 pm -1100
Posts: 225
endrik wrote:
I'm intrested in data concerning reed insulation mat. I have some results about the thermal transmittance and water absorption, but I don't have any data about the moisture transport properties.
I would like to know if you have done any simulations with reed insulation mat or do you have any measured data about reed insulation mat.

Hi Endrik,
we have no experience with reed insulation mats or material data about this material.

As long as the reed mats are not embedded in plaster, I would guess that the hygrothermal properties should not be too different from straw. In particular, if you are doing a one-dimensional simulation where the vapor and water transport occurs across the reeds (rather than along the reed stems), liquid water transport between the reed stems should be negligible, and only vapor transport needs to be taken into account, with a similar mu-value as for straw.

As always, doing some WUFI test calculations with slight variations of the parameters about which you are unsure will tell you whether the calculation results depend noticeably on the estimated parameters or not. If not, a plausible guess will be sufficient, if yes, more effort must be spent to determine the needed parameters with sufficient accuracy.

Regards,
Thomas


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 Post subject: Straw Bale
PostPosted: Thu Jul 12, 2012 6:08 am -1100 
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Joined: Thu Jul 12, 2012 5:50 am -1100
Posts: 1
Hi

I am doing a masters thesis on rainscreen cladding for straw bales. I currently have the 3 month temporary licence for WUFI Pro 5.0 and I am struggling to input a user defined material for straw. I have all the basic values but I am struggling when it comes to the hygrothermal functions and dont know figures to plug in here.

When I run simulations there is no moisture being taken on board by the straw. Can anyone help with this issue? Think I need to enter figures in the liquid transport co efficient section maybe?

Also I have tried to download the straw bale material file but when I click on it a new window opens saying cant open page. (I am using firefox, is this an issue?)

Any help would be greatly appreciated

Cheers

Paul


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 Post subject: Re: Straw Bale
PostPosted: Thu Jul 12, 2012 9:02 am -1100 
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WUFI Administrator
WUFI Administrator

Joined: Sun Jun 19, 2005 10:33 pm -1100
Posts: 225
PaulG wrote:
When I run simulations there is no moisture being taken on board by the straw. Can anyone help with this issue? Think I need to enter figures in the liquid transport co efficient section maybe?

Hi Paul,
the WUFI calculations done by IBP for the quoted report achieved good agreement with the measurements without using any liquid (i.e. capillary) transport. So this would appear to confirm the expectation that liquid transport is negligible and moisture transport happens by vapor diffusion.

Maybe a problem with the moisture storage function, or with the diffusion resistance factor?

Quote:
Also I have tried to download the straw bale material file but when I click on it a new window opens saying cant open page. (I am using firefox, is this an issue?)

I've sent you the project file by email.

Regards,
Thomas


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