A carbon negative mud brick house
Peter Hickson of Earth Building Solutions, engaged eTool to run a retrospective life-cycle assessment on one of their existing mud brick building designs to quantify the carbon emissions of the building. The mud brick house incorporates a number of sustainable design features that contribute to its environmental performance.
- Date: February 2014
- Client: Peter Hickson
- Builder: Peter Hickson and Earth Building Solutions
- Location: Woodhill, NSW
Passive Solar Design
Along with striking features such as curved walls and cantilevered alfresco roofing, the building also utilises passive solar design features to maximise winter solar heat gains. The building stretches along the east and west to expose the main living areas to the northern sun. The winter sun is able to penetrate the living areas of the house and heat up the thermal mass floor and walls during daylight hours which is then slowly released back into the house throughout the night when external temperatures drop. Areas or rooms with low occupancy rates such as the bed, laundry and bathrooms are located towards the east, west and southern side of the building.
Building materials with high thermal mass but low insulation properties generally rate poorly in HERS assessments due to limitations in software and assessment methods. Nevertheless, thanks to thoughtful passive solar design, reasonable size of the building and suitable amount of glazing in the appropriate areas, the building still achieves a 6 star thermal performance with 90% of the energy load for heating.
The mud brick wall itself is 40% less carbon intensive than a standard brick veneer due to low energy requirements and long lifespan of materials. The mud brick wall requires less assembly effort and lower recurring impacts due to the materials lifespan. The clay render internal finish also has a lower carbon impact compared to a brick veneer wall due to its lower repainting requirements. Manufacturing of mud bricks can be labour intensive and depending on where the trade staff is coming from, the transportation can have a significant impact on overall results.
The operational energy of the building is “carbon negative” since it produces more energy and provides CO2e savings than it consumes, thanks to a 3kW Solar PV system. The building also features appliances that use renewable low carbon intensity energy sources such as slow wood fire combustion for cooking, space heating and boosting the solar hotwater system. Due to the excellent thermal mass properties of mud brick, the building does not use any cooling systems other than ceiling fans.
With the combination of Solar PV power generation and low carbon biomass systems, the operational carbon of the building achieves a Platinum rating at -940kgCO2 per year per occupant.
The building is not connected to mains water or sewerage. All water comes from a spring and toilets are dry composting with grey water reused in orchards.
Clay based paint and render finishes throughout.
Only slate floor covering throughout which has low recurring maintenance impacts than carpets.
Predominantly recycled timber used in building.
This assessment was conducted by Fei.