Natural building, green building

Natural building, green building

Building materials have undergone a speedy evolution over the past century. Standard dimensions and shapes, predictable qualities, and manufactured precision make it quicker and easier to design and construct new buildings with laserflat walls, straight and sharp corners, and glass-smooth floors.

For many people, the more crisp, precise, and shiny a building is, the more perfect it is. However, there are those who feel that the increased standardization and predictability of building materials has resulted in our homes becoming sterile, uninspiring, and uninspired.

That’s not really a revelation; half a century ago, Frank Lloyd Wright wrote that “new machine-age resources . . . [do] not require that all buildings be of steel, concrete, or glass.” The symptoms of boring architecture are treated in many ways, often by adding more architecture. In a paper titled “Using Less Wood in Buildings,” architect Ann Edminster wrote that “fussy, trendy, anachronistic rooflines, cupolas, and turrets [in] contemporary suburbs are palliative attempts at endowing these spiritless developments with aesthetic substance.”

Inside, occupants spice up bland interiors however they can. By contrast, the stimulating charms of pre-industrial, “old-world” construction and indigenous architectures include a nonuniform visual character inherent in the materials and processes used. The irregularity of the underlying materials contributes in unexpected ways to both finish and structure. Light catches and plays on hand-plastered walls; subtly imperfect floors offer sensory interest; unusual corners lend variety.

Combining this aesthetic with excellent thermal performance, longevity, occupant comfort and satisfaction, and a keen eye toward deep environmental concerns—and the ability to do it cost-effectively—is a challenge that the natural building movement endeavors to meet. But an aesthetic appeal is certainly not the only driver—many natural buildings are virtually indistinguishable at a glance from normal construction; they have flat walls, distinct corners, normal roofs.

The term natural building has commonly come to mean using local, pre-industrial building materials and techniques whenever possible. These primarily include rough wood, clay and sand, stone, and— the most ballyhooed material of the movement for some time—straw, usually baled. Cob (a monolithic, hand-formed cousin of adobe) captures the imagination of many for its sculptability and earthiness. Earthbags (flexible-form rammed earth using polypropylene sandbags) have increasing visibility and use in the movement. Cordwood construction (using short lengths of unmilled wood as masonry units) is a recognized option with owner-builders in forested environments.

Salvaged and repurposed detritus, such as car tyres, junk mail, and broken concrete chunks (“urbanite”), is sometimes included under the natural building flag as well. The list also includes such natural material systems such as clay plasters, earthen floors, thatch, and dry-laid stone foundations. Traditional techniques that have maintained a contemporary presence, such as timber framing, unmilled logs, adobe, and rammed earth are also considered natural building.

Each material and method has advantages, limitations, and its own set of requirements for appropriate use. Modern materials, products, and tools that can enhance performance, longevity, safety, healthfulness, and buildability are generally incorporated; but the emphasis is on using the lowest and most benign technology to best achieve what needs to be done. Though it causes some members of both communities to bristle, natural building can easily be considered a subset of green building. At the very least, there’s a significant overlap.

Natural building materials and techniques are generally low in cost but high in labor—making them most appropriate for small structures, built with lots of cheap time and muscle, usually provided by the owners.

One of the things that natural building accomplishes is the economics of building with natural materials. The efficiency of mass production is replaced by the efficiency of gathering materials locally. The balance shifts from material expense to labour expense.

Claims that natural buildings are very inexpensive and simple are generally overblown, particularly when those buildings are expected to meet contemporary expectations of housing. Such assertions are less common than they once were. The natural building materials most commonly cited lend themselves particularly to the walls of a house, which typically represent just 7–15% of the cost of a structure—savings in these cases don’t account for the foundation, roof, windows and doors, mechanical systems, or any level of finish.

The natural building movement is evolving rapidly. In many ways, it’s following the path forged by the larger green building movement; in some ways, it goes beyond green building, taking that ethos to its furthest reaches. But, ultimately, those distinctions don’t really matter.

Examples of Sustainable Building Methods

Cob is a very old method of building with earth and straw or other fibers. It is quite similar to adobe in that the basic mix of clay and sand is the same, but it usually has a higher percentage of long straw fibers mixed in.
Instead of creating uniform blocks to build with, cob is normally applied by hand in large gobs (or cobs) which can be tossed from one person to another during the building process. The traditional way of mixing the clay/sand/straw is with the bare feet; for this reason, it is fairly labor intensive.

Some of the process can be mechanized by using a backhoe to do the mixing, but that diminishes the organic nature of it. Because of all the straw, cob can be slightly more insulating than adobe, but it still would not make a very comfortable house in a climate of extreme temperatures.The wonderful thing about cob construction is that it can be a wildly freeform, sculptural affair. Cob was a common building material in England in the nineteenth century, and many of those buildings are still standing.

Adobe is one of the oldest building materials in use. It is basically just dirt that has been moistened with water, sometimes with chopped straw or other fibers added for strength, and then allowed to dry in the desired shape. Commonly adobe is shaped into uniform blocks that can be stacked like bricks to form walls, but it can also be simply piled up over time to create a structure.

The best adobe soil will have between 15% and 30% clay in it to bind the material together, with the rest being mostly sand or larger aggregate. Too much clay will shrink and crack excessively; too little will allow fragmentation. Sometimes adobe is stabilized with a small amount of cement or asphalt emulsion added to keep it intact where it will be subject to excessive weather. Adobe blocks can be formed either by pouring it into molds and allowing it to dry, or it can pressed into blocks with a hydraulic or leverage press.

Adobe can also be used for floors that have resilience and beauty, colored with a thin slip of clay and polished with natural oil. Adobe buildings that have substantial eaves to protect the walls and foundations to keep the adobe off the ground will require less maintenance than if the walls are left unprotected.

Adobe is a good thermal mass material, holding heat and cool well. It does not insulate very well, so 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. Another approach is placing insulating materials on the outside.

Rammed Earth
Ramming earth to create walls is at least as old as the Great Wall of China. It is really quite similar to adobe and cob techniques, in that the soil is mostly clay and sand.

The difference is that the material is compressed or tamped into place, usually with forms that create very flat vertical surfaces. Modern rammed earth typically utilizes heavy mechanized equipment to move and compress the material.

The walls are normally at least a foot thick to give enough bulk to be stable and provide the thermal mass for comfort. It is best to apply insulating material to the outside of the building to keep the interior temperature constant. The interior surface can be finished in a variety of ways, from natural oil to more standard surfaces. Rammed earth houses tend to have a very solid, quiet feeling inside.

Building with bales of straw has become almost mainstream in many parts of the world, particularly in Australia and parts of the US.

Straw is a renewable resource that acts as excellent insulation and is fairly easy to build with. Care must be taken to assure that the straw is kept dry, or it will eventually rot. For this reason it is generally best to allow a strawbale wall to remain breathable; any moisture barrier will invite condensation to collect and undermine the structure. Other possible concerns with strawbale walls are infestation of rodents or insects, so the skin on the straw should resist these critters.

There are two major categories of building with strawbales: load-bearing and non-load bearing. A post and beam framework that supports the basic structure of the building, with the bales of straw used as infill, is the most common non-load bearing approach. This is also the only way that many building authorities will allow. While there are many load- bearing strawbale buildings that are standing just fine, care must be taken to consider the possible settling of the strawbales as the weight of the roof, etc. compresses them.

Erecting bale walls can go amazingly quickly, and does not take a lot of skill, but then the rest of the creation of the building is similar to any other wood framed house.

Cordwood construction utilizes short, round pieces of wood, similar to what would normally be considered firewood. For this reason this method of building can be very resource efficient, since it makes use of wood that might not have much other value.

Cordwood building can also create a wall that has both properties of insulation and thermal mass. The mass comes from the masonry mortar that is used to cement the logs together, and the insulation comes from the wood itself and the central cavity between the inside and outside mortars. This method produces a look that is both rustic and beautiful. The process of building is similar to laying rocks in mortar, where the the logs are aligned with their ends sticking out to create the surface of the wall and mortar is applied adjacent to each end of the log. Typically the logs are not coated with a moisture barrier, but are allowed to breath naturally. It is possible to include other materials into the matrix, such as bottle ends that would provide light to enter the wall.

Recent experiments with the use of cob instead of cement mortar to join the logs have been encouraging and this method may provide a somewhat more ecological approach to cordwood building. In this case special care should be taken to have large eaves to keep water away from the wall.