[Strawbale] Strawbale CO2 Emission
Mark Bigland-Pritchard
mark at lowenergydesign...
Tue May 2 18:16:01 CEST 2006
Chug, Andrew, everyone -
The figure for embodied energy depends of course on what you include.
Would straw have been baled anyway? What distance are the bales being
transported?
I addressed this issue in an approximate way (there is, I think, no
other way to address it...) in my PhD thesis last year. The relevant
text is below - I hope the formatting comes out OK... My own
calculations are for "typical" conditions in the southwest of England,
where I was living at the time. The actual local figures will depend
heavily on the haulage distance.
atb,
Mark
2.1.2: Low ecological impact:
Straw is a natural agricultural waste material, requiring no industrial
processing. As all energy and resource inputs into crop growth are
aimed at maximising the yield of the grain, the energy and environmental
costs associated with use of the crop stalks are minimal, consisting
only of those resulting from baling and transportation.[i]
<#_edn1>^,[ii] <#_edn2>,[iii] <#_edn3>
As the energy costs of baling would, in almost all cases, be incurred
anyway, the embodied energy of straw used in building may therefore
usually be assumed to equal that involved in haulage of the bales to
site. For a typical 400-bale strawbale house (approximately 150 m^2
wall area, compatible with a 100 m^2 dwelling floor area) in Britain,
this is unlikely to exceed 3.5GJ, or about 250kg CO_2 emissions[iv]
<#_edn4>. This clearly represents a considerable saving over
traditional building materials such as brick, stone or concrete, and a
smaller (but still significant) saving over "natural" materials such as
timber or recycled products such as cellulose insulation. [This claim,
however, assumes that no re-baling is required. This is indeed the case
where adequate bales are available, but some builders have not always
found this to be the case and have therefore re-baled on site[v]
<#_edn5>. Even so, the energy consumption in baling is low -
approximately 0.34 GJ for 400 bales[vi] <#_edn6>, corresponding to about
25kg CO_2 emissions.]
To put these figures into context, let us compare the approximate
embodied energy values and carbon dioxide emissions corresponding to 3
different full wall assemblies of 150 m^2 area[vii] <#_edn7> and similar
insulation value. The results are given in table 2.1 overleaf.
While no serious attempt at precision is possible at present with this
type of calculation, it is clear that, even under the worst realistic
conditions, strawbale construction compares favourably on these criteria
with the principal competing low-U-value wall designs.
At the end of the building process, in contrast to much modern practice,
the majority of the building waste can be recycled or used as mulch,
reducing the load on municipal landfill and incineration facilities.
Edminster[viii] <#_edn8>, in commenting on the results of her thesis on
this subject, notes however, that misleading "greenwash" exists in
sections of the strawbale community as elsewhere. Largescale use of
concrete in foundations, steel in frames, and cement in plastering,
combined with large building dimensions, can result in a structure just
as resource-hungry (in terms of both materials and embodied energy) as
any conventional building. At the same time, she notes the potential of
the technology for minimal impact when thought through carefully. In an
article for an audience mostly composed of enthusiasts, she notes:
The results of my research and analysis show a startling spectrum of
environmental impact severity among approaches to designing with straw
bales. Examining only measurable indices of impact - embodied energy,
water consumption, and waste potential - ten- and hundred-fold degrees
of impact can be identified between different design options. In some
cases the impacts exceed those of conventional building systems. It
thus became evident that the potential for lessening environmental
impacts through deliberate design choices is substantial.[ix] <#_edn9>
Table 2.1: Comparison of embodied energy in different construction methods
construction
embodied energy / GJ
CO_2 emissions resulting from construction / t
clay- and lime-plastered strawbale wall: rebaling
sand
clay
lime
transport
*TOTAL*
0.35
1.0
0.15
6.0
3.5
*11.0 GJ*
0.03
0.07
0.01
0.36
0.25
*0.72 t CO_2 *
brick / lightweight concrete cavity wall: brick
cellulose insul^n
l/w concrete
plasterboard
transport
*TOTAL*
63.7
10.5
7.2
3.6
10.5
*95.5*
13.38
1.60
2.30* <#_ftn1>
0.55
0.75
*18.58 t CO_2 *
timber panel system:
timber
cellulose insul^n
plasterboard
transport
*TOTAL*
2.4
12.5
3.6
7.5
*26.0*
0.36
1.90
0.55
0.54
*3.35* *t CO_2 *
Strawbale construction, therefore, provides an opportunity for unusually
ecologically sound building, but does not guarantee it: a thorough
environmental audit of the whole process is still necessary if
ecological excellence is to be achieved.
------------------------------------------------------------------------
* <#_ftnref1> includes carbon dioxide emitted in cement production
------------------------------------------------------------------------
[i] <#_ednref1> *Edminster* A V (1995), */Straw Bale Construction:
Patterns for a Sustainable System/*, Masters Thesis, Department of
Architecture, University of California, Berkeley, CA, USA (also
available as: */Investigation of Environmental Impacts: Strawbale
Construction/*, design AVEnues, Pacifica, CA, USA)
[ii] <#_ednref2> *Hofmeister* R (1994:winter), */Straw-Bale
Construction: How Does it Stack Up?,/* The Last Straw, issue 5, Tucson,
AZ, USA
[iii] <#_ednref3> *Pierquet* P (1997:winter), */How Good?: Embodied
Energy of Insulation Materials,/* The Last Straw, issue 17, Tucson, AZ, USA
[iv] <#_ednref4> Calculations based on 2 trucks carrying 200 bales each,
and each with a 60-mile round trip
[v] <#_ednref5> *van der Zoom* H (2004:06), unscripted talk,
International Strawbale Building Conference, Kalø, Denmark
[vi] <#_ednref6> maximum figure obtained from calculations based on (i)
data provided on bale manufacturers' websites, and (ii) observation of
baling on a field in Carmarthenshire.
[vii] <#_ednref7> Calculations based on unit embodied energy costs from
various sources tabulated in: ed. *Thomas* R (1996), */Environmental
Design/*, London: E & F N Spon
[viii] <#_ednref8> *Edminster* A V, /op cit/
[ix] <#_ednref9> *Edminster* A V (1996:winter), */Strawbale Design:
Towards an Ecological Accounting/*, The Last Straw, Tucson, AZ, USA,
issue 13
Andrew Webb wrote:
> Closely related to the question is embodied energy, if that is a help
> to them. Straw bale has 0.24 MJ/kg or 31 MJ/m3 according to
> http://www.canadianarchitect.com/asf/perspectives_sustainibility/measures_of_sustainablity/measures_of_sustainablity_embodied.htm
>
>
> -AW
>
>
> Chug. wrote:
>
>> Greetings baleheads
>>
>> I have been asked this question to which I don't know an
>> answer........any input appreciated.
>>
>> bale on
>> Chug
>> chug at strawbale-building....uk
>> http://www.strawbale-building.co.uk/
>> .
>> Dear Sir/Madam,
>>
>> I am conducting research on using straw bale insulation for an energy
>> efficient housing project. I was interested in finding out how much
>> carbon
>> dioxide is emitted from one pound of strawbale. This information
>> seems to be
>> hard to find since strawbale isn't as widely used as other building
>> materials. If you could forward any information, that would be
>> exteremely
>> helpful. Thank you for your attention.
>
>
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>
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