This article gives you a crash course in the terminology and basic concepts of Natural Building, providing a glossary of common terms, a materials and methods reference guide, and descriptions of natural building materials and finishes.
Common Terms in Natural and Green Building
‘Natural building’ and ‘green building’ have their roots in the broader subject of ‘sustainability.’ Sustainability means harvesting or using a resource so that the resource is not depleted or permanently damaged. Even renewable resources can be used in a way that is unsustainable, such as harvesting trees faster than the forest is able to regenerate itself. Sustainability can also be applied to the subjects of energy and water use in a building, and to the waste products of that building.
‘Green building’ focuses the principle of sustainability on reducing the impact that our built environment has on the rest of the planet. Green building reduces environmental impact both in terms of the energy that is required to operate and maintain a building, as well as reducing the ‘embodied energy’ of the materials that go into building it. The embodied energy of a building material includes all of the energy that goes into extracting it from the environment, the manufacturing and processing of that material, its transportation costs, and the costs of recycling or disposal of that material at the end of its useful life.
Green building utilizes renewable and lower impact materials, renewable energy and reduced energy use appliances and design, water and waste recycling, rainwater collection and climate-tempering and climate-appropriate landscaping. It also makes use of some highly processed manufactured products; however, they are lower in environmental impact than their more commonly used contemporary counterparts.
Natural building is green building that places particular emphasis on using materials which are found locally in nature, and used in a raw or minimally processed state. Natural building places a higher value on human labor, craft and creativity rather than specialized skills, capital and technology. Natural building also places a high value on the ongoing health and well-being of the building’s inhabitants, as well as the surrounding environment. This concern also extends to the builders.
A Handy Reference Guide for Common Natural Building Materials and Methods
The most common elements used in natural building are: subsoil (various combinations of clay, sand and silt), grasses (including straw and bamboo), stone and gravel, wood (often rough-milled, and used sparingly unless you have a plentiful supply), and building lime (from limestone). The local availability of these particular elements, along with climate-specific design needs and the skillsets and sensibilities of the builders, are major factors in determining how and of what materials a natural building is made.
The following is the beginning of a glossary of common terms, techniques and materials used in natural building. These building blocks are composites of the above earthen materials, and some of the ways they can be used most effectively to meet different needs. In future articles we will talk more about the specifics of how these materials are used.
Natural Building Materials
Adobe: sun-dried mud bricks made of clay, sand, silt, straw and gravel, set in mud mortar to make massive walls which can be planar or curvilinear, and which can be structural or non-structural. Adobe can also be used for the roof of a dome or vault, eliminating the need for wooden roof framing.
Rammed earth: a moist mixture of clay, sand and silt which is tamped into forms to make massive, planar structural walls.
Cob: a wet mixture of clay, sand, silt and long straw which is hand-formed in place to make massive structural walls and other sculptural elements.
Light-clay, slip-straw or straw-clay: long straw that is coated with a clay slip and packed into forms to make planar, lightweight, insulated non-load-bearing walls used to infill between structural vertical elements of another material. Light-clay can also be used to insulate roofs and floors, and can be formed into insulated bricks.
Straw bale: Large compressed bricks of straw, bound with twine or wire, which are stacked to make planar or curvilinear walls. Straw bale walls can be either load-bearing or infill, and are highly insulated. Straw bales can also be used to make vaults or dome structures in areas with little rainfall.
Earthbag: Polypropylene or burlap grain sacks which are filled with damp earth and tamped to make linear or curvilinear foundations and load-bearing walls. Earthbags can also be used for the roof of a dome or vault.
Stone masonry: raw or cut stones which are dry-stacked or set in mortar to make linear or curvilinear foundations and load-bearing walls.
Compressed earth blocks: a mixture of dampened clay, sand, silt and gravel which is compressed by a machine into bricks, and used much like adobe.
Cordwood: short logs cut to uniform lengths which are set in mortar to make massive and insulated structural or infill walls.
Wattle and daub: A framework of stiff vertical sticks woven horizontally with thin, flexible saplings or split bamboo and covered with plaster to make thin non-structural walls and partition panels. Wattle and daub walls can also be left unplastered for ventilation, or used to create a double wall construction in which an insulative material is stuffed between the two wattle and daub walls.
Thatch: long stalks of water reed or straw which are tied into bundles and attached to a roof structure for an insulated and rain protected roof covering. Large leaves such as fan palm can also be used for thatch.
Papercrete: waste paper mixed with water into a pulp slurry, with sand and a small amount of Portland cement or lime added to make a lightweight, insulated material which can be formed into blocks, poured into forms, or used as mortar for non-structural walls, domes and vaults. Clay can be substituted for the Portland cement to make ‘fidobe’ (fibrous adobe).
Bamboo: the most useful plant on earth, bamboo is a fast-growing giant grass capable of spanning large distances and resisting large structural loads. Timber bamboo can be grown in temperate climates to replace structural lumber.
Natural Building Finishes
Earthen plasters: mud made from a screened mixture of clay, sand, chopped straw and/or manure; trowelled, hand-applied or sprayed onto earthen walls for protection from the elements.
Lime plasters: a mixture of building lime (made from limestone that has been burned and crushed), sand and sometimes fiber; trowelled or sprayed onto earthen walls for a weatherproof and durable coating.
Earthen paints: a coating made of either wildcrafted, screened colored clay or white pottery clay with pigments added, mixed with aggregates such as sand or mica and often wheat paste and powdered milk (to increase durability); applied like paint over earthen plasters, drywall or other surfaces to seal and beautify them.
Limewashes: a wash made of building lime and water, colored with natural pigments which can be painted onto an earthen wall to seal, protect and beautify them.
Earthen floors: durable and beautiful floors can be made using various combinations of earthen materials, poured or moist-packed into place, trowelled to a fine finish and sealed with oils or non-VOC sealers.