Bamboo: Bamboo is one of the fastest growing plants in the world and can be harvested within 5-10 years. It is a grass rather than a wood, so it is very renewable. Structurally, bamboo is as strong as wood or steel. It can be used for flooring, furniture, beams, scaffolding and more. Bamboo grows quickly without pesticides or fertilizers so it has low environmental impact. Its strength and renewability make it a excellent sustainable building material.
Hemp: Hemp is a variant of cannabis that is grown for its strong fibers rather than its psychoactive compounds. Hemp grows very densely and absorbs more CO2 than trees. It has high tensile strength and can be used to make durable, environmentally friendly concrete blocks that are strong enough for load-bearing walls. Hemp fibers mixed into concrete or plaster improve acoustics and fire resistance of the finished material. The blocks are very energy efficient to produce with minimal embodied energy or waste produced.
Straw bale: Straw bale construction involves stacking tightly compressed straw bales and plastering them with a lime-based plaster to form walls. Straw is an agricultural byproduct that would otherwise be burned as waste. The bale walls have outstanding insulation properties, keeping buildings naturally cool in summer and warm in winter without requiring much energy for heating and cooling. They are non-toxic, pest resistant and fire retardant. Their texture also has natural beauty. Over time the plaster eventually petrifies the straw into an almost stone-like material.
Rammed earth: Rammed earth construction uses gravel, sand, clay and natural pigments that are densely packed into molds or forms to create load-bearing walls. The materials are all locally sourced, providing thermal mass for natural temperature regulation. Rammed earth has a low embodied energy and sequesters carbon in the building materials. Unlike concrete, it is breathable and allows moisture to evaporate so does not trap damp. With a smooth finish the walls resemble adobe and the technique has been used for centuries worldwide.
Mud/cob/adobe: These traditional earthen building techniques utilize the same locally excavated sand, clay, gravel and straw but form the walls differently than rammed earth. The wet mixture is either hand-formed into blocks called adobe or compacted into walls called cob or mud building. The natural materials are all renewable and sequester carbon as the walls dry. Thermal performance is outstanding with respiratory walls. Earthen walls also have anti-microbial properties supporting healthier indoor air quality.
Lime/limecrete: Lime is a binding agent made by heating limestone, a abundant natural material. Mixed with sand and gravel it forms the ancient building material limecrete or lime concrete. Lime has self-healing properties allowing cracks to close over time, improving longevity. It regulates indoor humidity and has antibacterial properties. The heat-curing process sequesters more CO2 than Portland cement curing. Lime also has a lower carbon footprint to produce than cement and allows structures to breathe naturally.
Wood: Sustainably harvested and certified wood is a renewable resource if sourced responsibly from managed forests. Wood provides excellent warmth, beauty, flexibility and has a low initial embodied energy to produce compared to other materials. New technologies also allow the use of agricultural waste wood fibers that would normally be burned as fuel. Cross-laminated timber (CLT) made from these fibers provides a strong, flexible building system suitable for multi-storey construction that sequesters the carbon stored in the plant fibers.
There are a growing number of additional sustainable construction materials in development as the industry innovates to reduce its environmental impact, such as mycelium-based materials like mushroom brick, agricultural waste fiber composites, and carbon sequestering geopolymer cements. Using locally available renewable and low-embodied energy materials wherever possible supports green, healthy construction practices that minimize waste and operational energy demands. The materials described can form the basis of structures that have smaller ecological footprints through their production, use and eventual reintegration with the biosphere at end-of-life.