Eco-balance of building with bales of straw – a comparison - Architekt Dirk Scharmer

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Eco-balance of building with bales of straw – a comparison

Eco-balance of building with bales of straw – a comparison
Building with straw, wood and clay is extremely sustainable and environmentally friendly. As long as the remaining construction materials are well selected, buildings whose exterior components are made of straw, wood and clay have a much better eco-balance than traditional buildings. This can imply that a straw bale insulated house uses less energy for manufacturing and heating – even if the required heat energy throughout its whole life cycle is taken into account – than a traditional building under unfavourable conditions uses merely for manufacturing.

The energy (nonrenewable primary energy) used to manufacture a 200 square meters straw bale insulated exterior wall of a one-family home compared to a conventionally constructed exterior wall (double-shell masonry, mineral wool insulation) points out a difference in energy demand that amounts to eleven years of heating.

 

Detailed comparison of wall structures throughout their life cycle
The energy demand for manufacturing as well as the transmission heat loss of three different wall structures, each featuring two different insulation qualities, will be analyzed.

Insulation qualities
Minimum standard of a passive house: U-factor of 0,15 W/m²K
Upscale standard of a passive house: U-factor of 0,105 W/m²K

Wall structures
SB Kalk-Lehm (lime and clay): Wall made of straw bales with lime plaster outdoors and clay plaster indoors
HR MW: Mineral wool insulated timber frame wall
StB WDVS: Reinforced concrete wall with a thermal insulation system based on polystyrene

Data
QT50 : Amount of the transmission heat loss corresponding to a 50 years’ life span of the construction element in kWh per sqm of the exterior wall and an assumed primary energy factor of the heating installation of 0,6
PEI nre: Energy demand for the manufacturing of the wall structures in kWh per sqm (nonrenewable primary energy)

Result
At the very first day of its life span the reinforced concrete wall has used as much nonrenewable primary energy as the straw bale wall not only for its manufacturing but also for its usage over a period of 50 years (according to the transmission heat loss). In other words, as the energy consumption for its manufacturing is tremendous, an even properly insulated reinforced concrete wall leaves the same ecological footprint at its very first day of life as the straw bale wall when its life span has expired. And the disposal, which is much more ecologically friendly when it comes to walls made of straw, wood and clay, isn’t even taken into account.

Primärenergiebedarf von Wandkonstruktionen kombiniert mit Transmissionswärmeverlust während der Lebensdauer
 
 
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