This is the seventh post in our Super Natural Materials series - you can view the whole series here.
How do you use straw in construction?
Straw-bale construction is a building method that uses bales of straw as structural elements, building insulation or even both – it's a sustainable method for building, from the standpoint of materials and energy needed for heating and cooling. The construction typically consists of stacking rows of bales, often in running-bond, on a raised footing or foundation, with a moisture barrier or capillary break between the bales and their supporting platform.
Bale walls can be tied together with pins of bamboo or wood, which add to the sustainability factor of the material. Alternatively, you can use wire meshes, then plaster either with a lime-based formulation or earth/clay render. Bale buildings can have structural frames of other materials, too – bales can simply serve as insulation.
Compressed straw bales have a wide range of documented insulation values. R-Value is a measurement of a material's insulating quality – the higher the number, the more insulating. The reported R-Value ranges from 17-55 (in American units). Bale walls are typically coated with a thick layer of plaster, which provides a well-distributed thermal mass.
Benefits of building with straw:
- Made from waste product - once the edible part of the grain has been harvested, the bales of straw give a new life to the material.
- Great insulation - the thicker the bale, the better the R-Value.
- Low-embodied energy - very little energy goes into the manufacturing of the product. Sunlight is the main source of energy for the plant.
- Biodegradable - straw bales are 100% biodegradable; homes made from straw can last over 100 years if maintained properly and when the time comes, the straw bales can be plowed back into the earth.
Examples of building with straw:
BaleHaus at the University of Bath
"BaleHaus is an innovative two-storey straw building, constructed on campus using ‘ModCell’ - pre-fabricated panels consisting of a wooden structural frame infilled with straw bales or hemp and rendered with a breathable lime-based system. The system delivers a sustainable method of construction, combining the lowest carbon footprint and the best operational CO2 performance of any system of construction currently available. Straw offers the perfect material for environmentally friendly construction due to its renewable nature. Monitored for two years for its insulating properties, humidity levels, air tightness and sound insulation qualities, the research team established that the building maintains heat through very cold winters, stays dry and produces good sound insulation." - University of Bath
Straw House in Pembrokeshire
This home, situated in St Dogmaels on a woodland hilltop, overlooking breathtaking views of the Cardigan estuary in Pembrokeshire was the winner of the Grand Design Eco Home Award in 2008. Nicknamed Quiet Earth Retreat, is boasts two storeys and is an off-grid home, powered by the sun and wind. The home is an all-round sustainable property.
You can even book to stay at this home, here.
NO99 Straw Theatre
In 2011, Estonian studio Salto Architects completed a temporary summer theatre in Tallinn made of black spray-painted straw bales. The stage was put into place for six months to celebrate the city's status as 2011's European Capital of Culture.