This isn’t a house that insulates to keep the warmth in. No, this house is truly a self-heating home. With walls made of composting straw, the house continually radiates energy inside, keeping the building at a comfortable temperature. Luckily, the smell is kept out at the same time.
The house, called ‘A Recipe to Live’, is a project at Waseda University in Japan, and it features some clever details that make this design much more than a walk-in compost heap. The walls of the house use a simple wooden skeleton design. In between the beams dried straw, which is frequently an agricultural waste-product, is packed into transparent acrylic boxes.
During the warm summer, the sun’s energy slowly dries the straw, keeping it from rotting. This also releases moisture from the straw, which helps to keep the building cool. Meanwhile, the façade is an orthogonal pattern of pretty plastic.
As the weather turns colder, the straw begins to ferment inside the boxes. This turns it into compost. As the composting process continues, it breaks down the organic compounds in the straw, which generates heat. Amazingly, this is a nearly constant source of energy at around 30°C. The technique is called bokashi (‘gradation’), which uses micro-organisms to speed up the composting process. Heat is generated for up to four weeks.
The Japanese team designed and built the straw house in a rural setting. This means the house’s cycle fits in well with agricultural life. Straw is locally sourced, and the entire composting process happens almost without any upkeep or external input.
Each wall is replaced several times a year, meaning that together, the building’s façades produce enough energy to warm – and cool – the straw house throughout the year.