○Housing Design
Many Japanese houses have low insulation performance, so no matter how much heating is used in winter, heat is lost, and condensation forms on the windows. Continuing heating under these conditions results in wasted electricity. Therefore, insulation materials are used to eliminate areas where heat escapes. By adding double glazing and 24-hour mechanical ventilation, it becomes possible to use heating and cooling 24 hours a day throughout summer and winter while keeping electricity consumption low.
Also, concrete used in buildings, apartments, and houses emits a large amount of carbon dioxide during its manufacturing process, significantly impacting global warming. Hence, it is necessary to reduce its usage. Considering these issues, as well as urgent responses to poverty and refugee problems where adequate housing is unavailable, and thinking about sustainable housing worldwide that can be started even now, the basic materials become early-growing paulownia, bamboo, straw, earth, clay, stone, lime, and water.
Straw is made by drying the stems of rice or wheat. Rice is widely cultivated across Asia, from Japan to India. Wheat is grown worldwide, including Africa, Europe, Asia, Russia, Australia, Canada, and Argentina. Therefore, straw can be obtained almost anywhere. Bundled straw blocks about 50 cm wide are used as insulation material, stacked between the pillars of a house. Earth is then plastered on both the inside and outside of these straw walls to create earthen walls. Such houses are called straw bale houses. The bales are produced by a farming machine called a baler, which compresses hay or straw into block shapes.
Furthermore, construction methods like cob and adobe, which mix sand, clay, straw, and water to make earthen or brick walls, have been seen on all continents since ancient times. When fibrous materials such as straw are mixed in, the long, thin straw strands connect the earth particles, increasing the tensile strength of the cob. Because these earthen walls weaken when exposed to wind and rain, an outer layer of plaster such as lime mixed with oil is applied to improve water resistance and durability.
The interior earthen walls also store heat from sunlight in winter. This allows warmth to persist even after the sun has set.
Heat storage differences by wall thickness
To maximize heat release during the night, the following elements are important:
・The interior wall surface is ideally left as bare earth (or a material with higher heat absorption than lime plaster).
・Warm air outlets are installed close to the walls to evenly warm the entire wall surface.
・High-insulation windows and fittings are used to prevent outside air intrusion.
Prout Village Housing Design
Category | Item | Content |
Design Policy | Sustainability | Housing centered on renewable plant materials and local resources, following natural cycles |
Environmental Consideration | Reducing CO₂ emissions by minimizing concrete use and employing biodegradable materials | |
Global Applicability | Adoption of traditional construction methods used since ancient times on each continent (e.g., straw bale, cob) | |
Main Materials | Early-growing Paulownia | Used for pillars and furniture. Can be harvested every 5 years. Adaptable worldwide in warm climates |
Straw (Straw Bale) | Harvestable worldwide. Used as insulation and wall material. Thermal conductivity 0.05–0.09 W/(m·K) | |
Earth & Clay | For earthen walls and bricks. Used in adobe and cob construction. Requires protection from drying and rain | |
Stone & Foundation Stones | Used for stone foundation structures. Helps disperse earthquake energy | |
Lime & Water | Used for plaster, wall coatings, and reinforcement materials. Materials that return naturally to the earth | |
Construction Techniques | Straw Bale | Straw compressed into 50 cm thick blocks and stacked between pillars. Earth walls formed on the exterior |
Cob & Adobe | Earth, straw, and water mixed and kneaded to form thick earthen walls with strength and fire resistance | |
Bamboo Laths + Earth Plaster | Used for interior partitions. Traditional Japanese technique | |
Thatched Roof | A traditional roofing method in which thatch materials such as miscanthus (Japanese pampas grass) and reeds are bundled thickly and laid at a steep pitch. It provides high thermal insulation and humidity regulation, with the roofing material itself functioning as the insulation layer. | |
Wall Thickness | Interior Earthen Walls | Target thickness: 20–30 cm |
Thermal Insulation Performance Comparison | ① Glass Wool | Approx. 0.016 W/(m·K) (highest insulation) |
② Straw | Approx. 0.05–0.09 W/(m·K) | |
③ Thatch | Approx. 0.041 W/(m·K); hay approx. 0.037 W/(m·K) | |
④ Earthen Wall | Approx. 0.5–0.8 W/(m·K) | |
⑤ Wood | Approx. 0.1–0.2 W/(m·K) | |
⑥ Concrete | Approx. 1.7–2.3 W/(m·K) (low insulation) | |
Moisture and Rain Countermeasures | Roof Design | Eaves and drip edges extended sufficiently to block rainwater |
Foundation Height | Raised to prevent splashback onto walls | |
Ground Moisture Barrier | Ensures ventilation and insulation layers between ground and structure | |
Ventilation Method | Air layers inside walls to release condensation and moisture | |
Foundation Structure | Stone Foundation (Primary Choice) | Pillars placed on foundation stones. Structure disperses earthquake energy and is reusable |
Concrete Foundation (Alternative) | Limited use as needed. Policy to minimize usage |
Since the supply of straw is limited, the following materials can also be considered as insulation alternatives:
⚫︎Miscanthus and reeds: Can be used as alternatives to straw, either bundled or compressed, for thermal insulation and cavity infill
⚫︎Wood chips, bamboo chips: Can be compressed into panels or wall materials
⚫︎Paper, cardboard (cellulose): Can be shredded and compressed into lightweight insulation
⚫︎Soil/clay mixed with organic matter (straw, grass): Hybrid material combining heat storage and insulation
If there is a sudden influx of settlers and it takes time to procure insulation materials, houses can be completed with adobe walls first and made habitable. Later, once insulation materials become available, they can be applied to the exterior to complete the construction. Therefore, the design should allow for future expansion.
○Household Wastewater
The main wastewater from a household comes from the washing machine, kitchen, washbasin, bathroom, and toilet. To process these collectively, a flush-type bio-toilet is used. This system directs household wastewater into a fermentation tank where microorganisms purify the water to a potable level. These microorganisms decompose human waste as well as toilet paper. The water used for flushing is rainwater collected in a tank. The facility avoids petroleum-based piping materials, instead using ceramic pipes fired at temperatures above 1000°C made from clay. With this setup, all household wastewater is processed together, eliminating the need for sewer systems, and the purified water is returned directly to farmland.
○Tooth Brushing
Brushing teeth begins with cleaning between teeth using dental floss. Then, gargle with hypochlorous acid water to sterilize and prevent infection, brush teeth using natural mineral toothpaste, and finally rinse lightly again with hypochlorous acid water. Hypochlorous acid water is harmless to the human body and is simply made by passing electricity through saline solution.
Hypochlorous Acid Water (HOCl)
Natural Mineral Toothpaste Ingredients
Rare Metal-Free Electric Toothbrush
While manual toothbrushes are good, using an electric toothbrush helps prevent cavities more effectively.
In a monetary society, it is recommended to visit the dentist every three months for regular checkups and tartar removal. In Prout Village, to reduce the burden on medical care, each household practices early tartar removal from a young age. Dentists are consulted only for hard and stubborn tartar.
○Soap
Natural-origin soaps are also produced.
Vegetable-based Soap
Wood Ash Soap
○Compost
Regarding waste processing, in a self-sufficient society like Prout Village, there are no supermarkets or convenience stores, so there is no waste from non-biodegradable containers or packaging such as plastic bags, PET bottles, cans, or glass bottles. In other words, the remaining waste consists only of kitchen scraps and biodegradable containers. Therefore, Prout Village uses compost. This operates on the same principle of “decomposition and composting of organic matter by microorganisms.”
○Small Washing Machines and Washing Facilities
Disposable diapers for infants and nursing care are made by cutting down forests. Burning used wet diapers requires stronger firepower, which emits more CO₂. Therefore, cloth diapers are the first choice. Using chemical fiber diapers can cause itching, so natural materials are used. Since infants, elderly people, and care recipients come and go in every residence, all houses are equipped with small washing machines and washing areas for cloth diapers.
○Rules for Housing Construction
Overall
・Designed so residents can assemble by hand
・Basic housing shape is circular and two-story
・In Japan, housing plots about 16m diameter, house diameter about 12m
・Housing for multi-generational families (6 people), elderly-use homes, single/shared houses (6–8 people)
・Elderly homes assume mobility impairments, wheelchair users, bedridden residents
・Structure should be beautiful and artistic to influence residents’ inner peace
・Windows and doors corners are rounded as a basic rule
・Around houses install solar water heaters, thermal storage tanks (heating), hot water tanks, water supply tanks, chilled water tanks (cooling, secondary option)
・Solar water heaters installed as carport roofs
・Build on stable ground, not soft or weak
Materials
・Primary materials: early-maturing paulownia (Sosei-giri), bamboo, straw (wara), soil, clay, stone, lime (used sparingly), water
・Stone-post foundation (Ishibadate) is first choice
・Concrete basically not used but exceptions exist
Overall Construction
・Use roofs that reliably handle rainwater with appropriately sized eaves and window drip edges to protect walls
・Raise foundation to protect walls from rainwater splashes from ground
・Prevent ground moisture from entering walls
・Exterior insulation for high airtightness and thermal insulation
・Double or triple glazed windows
・Mold-resistant construction
・Window placement avoids interiors visible from neighbors
・Soundproof all rooms
・Stairs, doors, hallways wide enough for large items like grand pianos
・Power sources include magnesium batteries, tidal power, small/micro hydropower, small/medium wind power, plant power, sand batteries, solar water heaters, solar thermal panels depending on conditions
・Use compost for kitchen waste
・Large drains in bath, washroom, kitchen to prevent clogging
・Provide washing places near bath for cloth diapers and elderly/infants after excretion with clog-resistant drainage
・Windows, doors, insulation, wiring, paint made from naturally degradable materials
Natural Disaster Measures
・Prevent underfloor and 1m above ground flooding from heavy rain
・Durable against Nankai Trough earthquake shaking
・Furniture, interior, lighting designed for major earthquakes
・Minimum 4m distance between houses
・Salt damage countermeasures for outdoor equipment near sea
・Power system can receive electricity via underground cables from other regions in case volcanic ash clouds block sunlight
・Roof designed for easy volcanic ash removal
・Roof designed for manual snow removal safely for elderly or electric heating snow melting system considered
・Confirm resistance to tornado/hurricane wind forces with anti-flying measures
・Confirm strength against fallen trees in typhoons
・No falling/flying objects during typhoons
・Lightning protection measures
・Outlet caps on all power sources to prevent fire
○Hemp
Hemp is a sustainable material that requires no rare metals, is strong and versatile, and has a low environmental impact. Therefore, in Prout Village, hemp is utilized in various fields.
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