Buildings with Plastered Interior and Exterior Finishes Applied directly to Straw Bale Walls
The first straw bale building constructed for research purposes in Japan is known as “Atom House”. It is located at Nihon University’s Center for Natural Environmental Sciences in Fujisawa City, Kanagawa Prefecture. Atom House was designed by Mirai Tono, Koji Itonaga, and students of Nihon University’s Architecture and Regional Ecological Design Studio. Construction began in 2002 and was completed in 2006.
The exterior of Atom House’s straw bale walls are finished with approximately 50mm of fermented clay loam mixed with straw (Jp: Arakabe) as a base coat, 10mm of earthen plaster as a second coat, and 5mm of earthen-lime plaster as a finish coat. The interior is finished with 10mm of lime plaster.
Atom House’s indoor environment is unconditioned but designed for passive solar gain using a south facing window and rammed earth trombe wall.
Straw bales are a moisture sensitive building material. It is often recommended to avoid the use of living/green and flat roofs in conjunction with straw bale walls. Unless meticulously detailed, constructed, and maintained, living roofs are a danger to straw bale walls. Atom House provides an example of a problematic living roof in conjunction with straw bale walls.
Cross Section of Atom House
Hareakara, a studio located in Arita, Wakayama Prefecture, was designed and built by Motoyoshi Murayama of Liveart. Unlike the previous buildings, Hareakara consists of straw bales stacked on edge surrounding a 2×4 frame. Both the interior and exterior are covered with earthen plaster. Construction began in June 2008 and the final exterior finish was completed in May 2009.
Mikio and Masami Sakai designed Square One, located in Higashikawa, Hokkaido. Construction of the bale walls and interior finish was led by Stefan Bell and the exterior Tosa Shikkui plaster was applied by Keisuke Noda. Unlike common Shikkui which consists of hydrated lime, seaweed glue and hemp fiber, Tosa Shikkui consists of fermented hydrated lime and straw. Tosa Shikkui is allowed to ferment for three years, which causes the straw fibers to break into thinner fibers and produce a glue-like substance, both of which improve workability. Tosa Shikkui is known for its weather resistance. Construction of Square One began in the spring of 2009 and was completed in the summer of 2010.