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EMBODIED ENERGY & SUSTAINABILITY - INTRODUCTION
 
It is estimated that buildings, their construction, operation and disposal, account for over 40% of the total energy consumption. The consumption of this energy has implications for the depletion of natural resources and for the production of pollution and problems such as global warming and acid rain. The total energy consumption that can be attributed to a building throughout its life will depend upon the energy consumed for the production of the building materials, construction, operation, maintenance and for demolition and disposal or recycling.
 
EMBODIED ENERGY
 
Buildings not only use energy, it also takes energy to make them. This is 'embodied' energy, which is all the energy required to extract, manufacture and transport a building's materials as well as that required to assemble and 'finish' it. As buildings become increasingly energy efficient, the energy required to create them becomes proportionately more significant in relation to that required to run them. This is particularly true because some modern materials, such as aluminum, consume vast amounts of energy in their manufacture. The common building material with least embodied energy is wood, (most of it consumed by the industrial drying process). Brick is the material with the next lowest amount of embodied energy, (4 times that of wood). From the perspective of embodied energy, every building, no matter what its condition, has a large amount of energy locked into it. This is yet another factor in favor of conserving and restoring old buildings, and for designing long life, loose fit buildings that easily accommodate change. Also, because the energy used in transporting its materials becomes part a building's embodied energy, this is an incentive to use local materials, thus helping the building to be embedded in place. Embodied energy is highly dependent on factors such as geographical location, technology employed in the manufacturing process, the degree of automation, mechanisation and local methods of manufacture, the value is by no means absolute and is different from on location to another.

 
SUSTAINABLE DESIGN

Smaller is better: Optimize use of interior space. Be energy-efficient: Use high levels of insulation, high-performance windows and tight construction. Use renewable energy: passive solar heating, daylighting and natural cooling. Design water-efficient, low-maintenance landscaping and gray water from sinks, showers etc. can be recycled for irrigation.
Spread the environmental impacts of a building over as long a period as possible to improve durability. Make sure the structure is adaptable to other uses, and choose materials and components that can be reused or recycled in the future.
 
SUSTAINABLE MATERIALS

Because manufacturing is very energy-intensive, a product that lasts longer or requires less maintenance usually saves energy. Where possible, select building materials that will require little maintenance or whose maintenance will have minimal environmental impact. Choose building materials with low embodied energy, heavily processed or manufactured products and materials are usually more energy-intensive. Locally produced building materials cuts transportation costs, and thus reducing pollution generation.
Building products made from recycled materials cut energy consumption in manufacturing and save on natural resources. Solvent-based finishes, adhesives, etc. release toxic compounds into the air and should be used to a mininum. Products with excessive packaging, is an energy waste and should be avoided
 
CONCLUSION
 
It surprises a lot of people to learn that a state-of-the-art, energy-efficient, passive-solar house built today may consume less heating and cooling energy over 30 or even 50 years of operation than was required to build it. This means that if our society wants to continue the impressive gains that have been made over the past 20 years in reducing energy use, we will need to focus attention on embodied energy as well as operating energy.
 
A sustainable alternative - Conventional vs Strawbale construction
Embodied energy
Embodied energy is the energy required to extract, transport, process, install, and dispose of, or recycle the materials that make up the building.
For this study, the total embodied energy was not used to compare the two construction types, only the energy for the material manufacture was used, because energies used to transport, install etc. would in most instances be the same for both construction types and cancel each other out, and because almost 70% of the total energy invested in a building's construction (Embodied energy) is embodied in the materials themselves, one can compile a rather accurate comparison with using just the energy used for the material manufacture alone, however, when referred to the energy used to manufacture the materials I will refer to the “Embodied energy”.
Materials which will be more or less the same in quantity / volume eg. ceiling boards, cornices, skirtings, floor slab & finishes, because of the same floor area, have been omitted for they will have no impact on the embodied energy outcome.
 
 
Construction
To compare the two types of construction, I started with a 12000mm x 6000mm brick building and included 2 bedrooms, a bathroom, open plan kitchen & living and a garage. To justify the  comparison, I designed the strawbale dwelling with the same rooms and exactly the same floor area for each room, but because of the bales’ rather wide (approx. 480mm) module width I ended up with a 13200mm x 7250mm external envelope for the straw bale dwelling. This made quite a difference on the material volume of the roof and roof trusses. Both the dwellings’ received one plaster coat, but vary in thickness. Conventional brick wall plaster width vary from apprx. 12mm – 18mm, compared to the 30mm plaster coat for strawbale walls because of the greater surface un-evenness among other reasons.
 
 
 
 
 
 
 
The foundation details differs from conventional brick buildings. The straw bales are laid on a bed of stone so they will not retain moisture. A cement screed is cast in the bottom of the trenches on the conc. footing to be sure that any water that might find its way into the trench would be directed away through the weep holes on the sides. These are the only bricks used in the strawbale dwelling, thus embodied energy values for mortar and bricks are a lot less for this type of construction. The foundations for strawbale buildings are shallower (200mm deep), thus less conc. Is used as well.
 
 
 
The last main difference is, of course, the wall material which differs hugely in the amount of embodied energy to produce & install them. Embodied energy for straw bales is 31MJ/m3 compared to the 5200MJ/m3 of stock bricks, thus because the walls have the greatest material volume of all the building components, it is understandable that the strawbale dwelling will have a much lower total embodied energy value than it’s rival as is indicated below.
 
 
 
Conclusion
Straw is a viable building alternative, plentiful and inexpensive. Straw-bale buildings boast superinsulated walls simple construction, low costs, and the conversion of an agricultural byproduct into a valued building material. Properly constructed and maintained, the straw-bale walls, plaster exterior and interior remain water proof, fire resistant, and pest free. Because only limited skill is required, a community house-raising effort can build most of a straw-bale house in a single day. This effort yields a low-cost, elegant, and energy-efficient living space for the owners, a graceful addition to the community, and a desirable boost to local farm income. I think, especially in this country, residential straw bale buildings could be a very sustainable viable alternative to our residential architecture.
 
Compilation & comparison tests done by JB, Architect & founder of Dreamhouses.co.za
 
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