A Straw Bale Sanctuary
Viva Living Homes recently commissioned eTool to perform an LCA on one of their existing straw bale homes to support a submission for the Master Builders Excellence Awards. It was clear while performing an LCA, that the Viva Living team carefully considered every aspect of their building, and strove for environmental performance. One of the issues that they faced however, as do a number of other builders, designers and architects often face also, was how to find the best answer for environmental conundrums such as comparative impacts of using standard local timber versus recycled timber from halfway around the world. Enter LCA and the quantifiable answers started to flow. This story is one we see often and it demonstrates how powerful LCA is for quantifying decisions and ensuring the best results. The LCA results for the straw bale home pointed to notable carbon savings compared to the benchmark and showcased a number of impressive sustainable design features.
- Date: April 2014
- Client: Viva Living Homes
- Builder: Viva Living Homes
- Location: NSW
Low Carbon Structure
This may be the most impressive element of the straw bale home. It’s very challenging tackling this element of a building’s carbon footprint, and it usually requires massive functional improvements to reduce the impacts/year/occupant. The straw bale home instead relied heavily on superior material choices with the inclusion of fly ash content in the slab, straw bale walls, timber structural frame, and earth/cob infill internal walls. Structurally the only material what wasn’t renewable was the Colorbond roof, but even this is a permanent material that can be recycled for generations to come.
Solar Passive Design
The NatHERs rating which covers the thermal performance of the building rated it at 8 stars which means the design nearly negates the need for artificial heating or cooling.
Renewable Heat Source
The bulk of the space conditioning load is a heating requirement. This is managed with solar collectors feeding a hydronic heating system. These solar collectors also supply hot water. The hot water loop is supplemented by the wood stove in the kitchen, which also supplies much of the cooking energy. Essentially all the heating loads in the building are met with renewable resources.
The remaining building integrated energy demand is met with efficient fittings. Ceiling fans meet the minimal cooling loads, leaving no need for air conditioning. LED lights compliment the fit out.
Low Carbon Finishes
The finishes inside and out are excellent in this design. Externally, a lime-earth render provides a weather barrier to the straw bale walls. Internally, the polished concrete floors negate the need for fired ceramics, or highly processed carpets. The walls are finished with an earth render. The earth render is in itself a very low carbon alternative to gypsum-based products, and also means that paint is not needed. Exposed timber is finished in natural oils.
The building has 2.14kW PV system, which supplies all the building integrated electrical loads, and much of the predicted appliance energy.
Off Grid Water
The building is “off grid” for water use. All water use is harvested rainwater from the roof. Not only does this lower the strain on distributed water supply sources, it’s also lower in carbon due to less pumping energy. The same is true for waste water treatment. The plumbing fittings look and function like normal within the house, but behind the scenes there’s a composing waste water treatment plant which deals with the sewerage in an energy efficient and low impact manner.
This assessment was conducted by Rich