Most of us are aware of the need to minimize fossil-fuel use, and limit the emission of carbon dioxide into the Earth's atmosphere. The construction industry produces an enormous amount of carbon emissions from the synthetic building materials produced by highly-industrialized processes, and the energy consumed in the construction of the built environment. There is a growing need to transition to methods of building, and construction materials, that are responsible for less carbon emissions in their manufacture and use.
Using a natural material when constructing new buildings or restoring old ones is 'low impact' in terms of eliminating or minimizing any lasting effects on the world in which we live. There is a growing interest in using natural materials and techniques that are based on old technologies, but tailored to meet future constructions needs. Unlike synthetic building materials, natural materials contain no harmful chemicals and can be vapor permeable; making it increasingly evident that these materials can not only maintain the structural fabric of the building, but also help keep its occupants in good health.
What are these natural building materials?
Hempcrete is a natural material comprised of chopped stalk of the hemp plant (shiv) mixed with a lime-based binder. It can provide a natural, healthy, sustainable, and low-embodied-energy building that creates a negative carbon footprint.
Hempcrete is not used as a structural element, but can be used for walls, wall insulation, flooring, roofing, and more. It is water-proof, fire-retardant, and rot-proof when used above ground, and is 100% recyclable. All loads must be carried by internal framing - wood stud framing is most common.
Hempcrete regulates the temperature and humidity of a building, making it an ideal building material for all types of climates, and potentially eliminating the need for heating and cooling systems. Hempcrete has been installed at temperatures that fall below freezing with no adverse effects, but working with hempcrete above 40 F is recommend.
Adobe is one of the oldest and most versatile natural building materials still in use today. It is made from primarily clay, sand and dirt. Other organic materials such as straw and dung can be added to improve the insulation properties of the structure. Typically, the mixture is formed into blocks, left to dry, then stacked like bricks to form a structure.
Adobe is a good thermal mass material, but does not insulate very well. Walls made of adobe need some means of providing insulation to maintain comfort in the building. Sometimes this is accomplished by creating a double wall, with an air space, or some other insulation in between.
Adobe is recommended as a building material in mostly warm and dry climates, but can be used colder climates with careful construction techniques. The constant freezing and thawing affiliated with colder climates can cause the bricks to crumble as they shrink and swell with the weather.
Rammed earth buildings start as form work - plywood structure that established the outline of a wall. A mixture of soils is then packed tightly between the forms by hand or machine. Once the soil is in place, the forms are removed, and a solid, stable wall remains. It is important that the soil mixture does not have too much clay or the finished wall will shrink and crack.
When completed, rammed earth walls can be left just as they are, or they can be finished with plasters, paints or siding. If left unfinished, the earth provides a natural, breathable wall, in comparison to artificial sidings with chemicals.
In desert climates the thermal mass of the walls can provide the sole means of heating and cooling, but in other climates, additional insulation or energy sources may be needed.
Straw bales were first used in construction over 100 years ago by homesteaders in the Midwest who had limited building materials. Today, some structures over 75 years old are still inhabited. Straw bales are a low-embodied-enery, natural building material made from an agricultural waste product. Straw is used in landscaping and animal bedding, but because of the large quantities produced, grain farmers typically burn much of their stalk waste. Burning this waste releases CO2 into the atmosphere creating pollution and poor visibility. Grain farmers are searching for more environmentally sound way to discard their stalk waste - straw bale structures are a great alternative.
The two basic types of straw bale construction are load-bearing and non-load-bearing. Load-bearing structures support the weight of the roof on the bales themselves without any frame work, and are limited to small one story buildings. Non-load-bearing structures typically use post and beam framing with straw bales filling in between. Buildings using the non-load-bearing method can be multiple stories if need be.
Straw Bale construction creates thick walls with good insulating properties, resulting in highly energy efficient buildings. The structures are also fire resistant due to the tightly compacted bales that deprive the flames of oxygen, and stucco/plaster finishes used specifically as fire-proofing.
Straw bale structures are ideal in mostly dry climes, acceptable in wet climates, but difficult to deal with in humid climates.
"A bale house can stay dry from rain and still be saturated with moisture inside the plaster due to the acclimation of the bales to the area’s relative humidity. Everything eventually settles on a moisture content that is in direct relation to the relative humidity of its surroundings." - StrawBale.com
Hempcrete, adobe, rammed earth, and straw bale buildings are the four natural material structures that I find the most viable and interesting. There are numerous other natural materials that are used in building applications all over the world.
Here are a few, check em' out: