Construction of a mud brick home

Earth Buildings – Proving the Importance of Embodied Energy

Fei Ngeow, eTool LCD Engineer, recently attended the 2014 EBAA Conference: ‘Earth Building – Towards Zero Carbon’, in NSW. The two-day conference was held the the Bamarang Bush retreat in buildings constructed with mud brick and included workshops and guest speakers on varying topics related to earth buildings.

Fei presented on the topic “The opportunity for earth buildings to achieve true environmental sustainability.” Some of our findings when comparing emissions of a brick veneer house with a mud brick house are shown below:

Life Cycle Performance Comparison

External Wall Comparison

Life cycle analysis shows that a 250mm mud brick wall has a 95% improvement in embodied CO2 over a 110mm rendered brick veneer wall.

Assumptions:
  • Mud brick wall – 250mm puddled mud brick wall made onsite, finished with 10mm clay/bitumen render.
  • Brick veneer wall – 110 brick, insulation, plasterboard paint internal finish, render external finish.
Screenshot 2014-10-14 16.33.03
Embodied Energy Comparison
When you consider the impacts for a whole house for the brick veneer and mud brick house, the embodied emissions are lower for a mud brick construction when compared to a benchmark brick veneer house.
Brick veneer house versus mud brick house - total embodied energy only
According to the IPCC, 1 tonne CO2/person/year  is considered the safe limit to maintain a stabilised climate  for  Interestingly, the embodied emissions in both situations are actually higher than this leaving no emissions spare for all other aspects of life such as transport, food, goods and services.  Assuming we leave around 0.7 tonnes/occupant per year for all other aspects of life we have a sustainable budget of about 0.3 tonnes/occupant/year for our dwellings.
Embodied & Operational Comparison
When the services (heating, cooling, hot water, cooking, appliances, and lighting) are included, the savings are not as clear, due largely in part to the NatHERS 6.5 star rating for standard insulated brick veneer house versus an uninsulated 4 star mud brick house.  Arguably, this reflects limitations in the NAThers modelling such as natural ventilation and use of non-standard designs or materials.  In reality a mud brick house has been claimed to outperform brick veneer in terms of thermal comfort.
Assumptions (for both houses):
  • reverse cycle heat pump (CoP = 3.65, EER = 3.4)
  • 85% efficient gas HWS
  • CFL lighting
  • gas cooking
Brick veneer versus mud brick

The house comparisons have been modeled in a cold climate zone (Tomerong)  and therefore have a minimal cooling requirement and high heating requirement. When low carbon alternative heating solutions such as wood pellet heaters are incorporated, the embodied emissions make up a larger proportion of the total.

Capture

Although the mud brick still requires more heating, because the heating source is very low in emissions in both cases the total operational energy decreases meaning, the embodied emissions proportionally increase.  The relative savings from the mud brick walls then become more significant. If houses can be designed optimally, to minimise cooling requirements, low carbon outcomes are easier to achieve through the use of renewable heat sources.

The grid emissions in the above two scenarios are assumed constant throughout the life cycle of the building.  In reality the grid emissions will decarbonise if Australia is to meet its commitments to Kyoto (80% reduction in CO2 by 2050).  Again the embodied emissions become more  significant because the operational makes up a smaller proportion of the overall emissions.

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Conclusion

The operational use can have a significant impact on the environmental performance over the life of the building.  However, embodied emissions can be arguably as important particularly when low carbon heating sources or future grid intensities are taken into account.  Operational energy use can be very variable depending on how conscientious the end-user is, it is also much easier to tackle through use of renewables and energy efficiency – measures that can often often be applied retrospectively. The embodied emissions on the other hand are locked in from the time the building is built.  By using low impact materials such as mud bricks these impacts are reduced significantly and the savings are locked in for the lifetime of the building no matter what kind of user moves in.
Likewise Earth builders still need to be knowledgeable about the services that go into the building and their life-cycle impacts to ensure that these won’t negate the environmental benefits of their earth home. This is where Life Cycle Design can be very handy – providing big picture comparisons to help the builder make choices that are better for the planet.
A big thanks to the Earth Building Association of Australia for putting on a great conference!
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