Natural Building Techniques - Part # 2 Natural Building Techniques - Part # 2
The Archibio architecture group in Quebec has updated the ancient sod roof of Europe with a concept called the "living roof." This type of roof has several advantages: it is an aesthetic feature, helps the house blend into its environment and provides climatic stabilization. Particularly useful in wet snowy areas, this style of earthen roof has more limited applicability in dry climates.
A living roof is built on top of a sufficiently strong frame with carefully applied waterproofing, as it is very difficult to locate leaks once the growing medium is in place. The living roof itself is a compost based system, usually a base of straw left to decompose within which native or introduced plants can then take root.
The living roof will need ongoing tending, and could be a fire hazard in hot dry climates. It is advantageous in that it protects the waterproofing from damage by ultraviolet radiation, and precludes the need for tiles or other shingles.
Natural Plasters and Finishes
Before the advent of portland cement, most earthen and masonry structures were protected by mud- or lime-based plasters. While still common in other parts of the world, lime and mud plasters are relatively rare in the U.S. The advantages of these plasters include "breathability," softness to the touch, aesthetic qualities, workability and easy reparability, as well as economy of materials. Less brittle than cement-based plasters, those based on lime or mud adhere and "move" with the underlying wall, lessening cracks and often making stucco netting unnecessary.
Because they can erode unacceptably when exposed to rain, exterior mud plasters are generally used in drier climates. Protected from rainfall and other liquid moisture, earthen plasters are viable in any climate. They have fallen into disuse in the U.S. because of their disadvantages of slow setting times, the perceived need to renew them every several years due to weathering, and discrimination against their use by building codes.
However, as the limitations of cement-based plasters become increasingly evident, many natural builders are returning to ancient plastering techniques from around the world. An extensive collection of traditional plaster and paint recipes and application methods can be found in The Straw Bale House and The Earthbuilders' Encyclopedia
Printer Eric Patterson of New Mexico has discovered a use for his (and anyone's) waste paper. He pulps this paper and mixing it with cement, makes lightweight, strong and easily-worked paper blocks. This material can also be poured and used as mortar or plaster. Only a few examples of this system with varying degrees of success currently exist.
While most recipes call for as much cement as is used in a solid concrete wall, some practitioners are experimenting with clay as a binder. Concerns include flammability with some examples having burned, and the effects of freeze-thaw.
Rammed earth is an ancient earthbuilding technique currently undergoing a renaissance in the U.S. and abroad. It has been revived in France by CRATerre, in Australia by Giles Hohnen and others, while its main proponent is the U.S. is David Easton, author of The Rammed Earth House (see Bibliography). These pioneers have updated the technique with improved engineering, sophisticated forms, and innovative design to make rammed earth competitive with conventional construction, even in earthquake-prone California. While rammed earth is in limited use in the U.S., builders in western Australia have captured up to 20% of the housing market in many areas.
Rammed earth has the advantages of excellent thermal mass (which in many climates may be a disadvantage unless insulated), strength, comfort and beauty. Rammed earth can be built with simple forms and tools with less handling than other earthbuilding techniques, as the material cures in the wall. It can be built in a variety of climates. Walls do not need to be plastered and will last for hundreds, even thousands of years (the great wall of China is partially built of rammed earth). It has been used to build structures of up to thirteen stories in Yemen.
First proceeding by setting up forms on top of an appropriate foundation (usually stone or concrete), a soil mixture with a clay content of 20% and a moisture content of 10% is then rammed in layers or "lifts" of 6-8 inches using mechanical or hand tampers. Different soil types can be used to create decorative effects and the whole is topped by a concrete bond beam which then holds the roof. Procedures are discussed in detail in The Rammed Earth House.
To build efficiently for the North American market, David Easton has developed sophisticated forms and tools which decrease time and labor costs. It is, however, still extremely labor intensive, and codes demand intensive reinforcing in earthquake-prone areas.
In an effort to make rammed earth even more competitive, Easton has developed a system called Pneumatically Impacted Stabilized Earth (PISE). In this system moist earth is sprayed against a single form allowing thick walls to be built extremely quickly.
Recycled Building Materials
In an effort to reduce waste, many builders are seeking to reuse materials which would otherwise end up as trash. Many structures, especially in urban areas, can be effectively rehabilitated, saving immense amounts of new construction costs, maintaining important cultural links, as well as avoiding massive amounts of landfill waste. Other structures can be carefully dismantled, saving lumber, bricks and other recyclables for new projects. High quality old-growth timber has been salvaged from old barns which is then used for new homes.
Waste wood can be reused to create a number of board products. Many of these, unfortunately, depend on toxic binders, but efforts to make healthy alternatives continue. Additionally, sawdust and recycled plastic have been used to create long-lasting lumber substitutes. Efforts in these areas have been spearheaded by the Wood Reduction Clearinghouse.
Windows, doors and other fixtures can be refurbished and reused, saving valuable architectural heritage and creating unique resources for owner-builders. Others use "junk" in innovative ways (see Earthships.)
The advantage of this approach is the obvious environmental benefits and aesthetic possibilities. Disadvantages include the time, labor and cost to build with old treasures because of refurbishment, special detailing necessary, and the time spent to find, dismantle and transport these resources.
Straw Bale Construction
The use of baled straw to create superinsulated walls has become an extremely popular method of construction in recent years. Most common in North America, bale buildings have been built around the world. Originally used by the pioneers of the Nebraska sandhills, straw bales are cheap to buy and easy to build with, lending themselves to "barn-raising" parties where structures and community are created at the same time.
Straw is an annually renewable crop, available wherever grain crops are grown. It is indeed a waste product, much of which is currently burned in the field. The thick walls offer superior insulation value when appropriately built. Bales are easy to work with, lightweight and require a minimum of tools. With a natural plaster, straw bale walls "breathe," and together with the sound absorbing qualities, provide a quiet, healthful interior environment. Straw bales can also be combined to great effect with other natural building systems. Straw bales are used either as infill in a post-and-beam structure, or as a load-bearing system where the bales themselves support the weight of the roof. The bale walls are commonly wrapped with stucco netting and plastered with mud, lime-sand or cement plaster. In many cases, the netting has been found to be unnecessary, and plaster is applied directly to the bales.
Structural, fire, and moisture tests have been done on the system with great success, leading to easier code approvals. Several insurance companies have insured bale buildings, and bank financing is becoming available. The system is also gaining acceptance with HUD and Fannie Mae, as well as with large home building organizations as Habitat for Humanity.
Straw bale construction has a few drawbacks; the walls tend to be "organic" and if not carefully built, can use excessive amounts of plaster. Appropriate bales can sometimes be difficult to locate, and if inadequately stored can be susceptible to damage by rain. Current code restrictions demand "overbuilt" systems which can increase costs, and a contractor-built straw bale house can be slightly more expensive than its stick frame counterpart. Straw-bale buildings have been built with code approval in every climate from New Mexico to Minnesota.
Because straw bale construction is still so new, innovations are continually being developed. An external pinning system shows great promise, as do the possibilities of vaulted and domed roofs entirely of straw bales. Straw is also being used to create compressed panels to replace plywood and as interior partition walls. Ongoing innovations are recorded in The Last Straw, an essential journal for the field.
The use of reeds, grasses or palm fronds as a roofing material is still common in Europe and many southern countries. This natural roofing material is of increasing interest to builders seeking an alternative to industrial roofing methods. Thatched roofs, if well built, can last up to sixty years or more, and provide a pleasing counterpoint to many of the wall systems mentioned here. Thatch breathes, can use local materials, is highly insulating, and is extremely beautiful.
Thatch, however, is a highly skilled and time-consuming craft, with only a few practitioners left. This can lead to excessive costs. If a thatched roof is not well built, it will need to be replaced within a few years, and is prone to leaks. Thatch can provide a home for undesirable pests, and fire danger is also a distinct disadvantage for improperly thatched roofs. In many countries in Africa, thatching grass is increasingly rare and expensive, and the desire for "modern" roofs has led to its decline.
Wattle and Daub
The technique of weaving branches (wattle) as a support for mud plaster (daub) is perhaps the oldest of earthbuilding techniques and is still used for traditional architecture in many parts of the world. Uncommon in the U.S., it can be used in mild climates to create thin earthen walls, but lacks the thermal mass or insulation desirable in other climates. An intriguing use of wattle and daub is to create interior partition walls.
Wood is an ideal building material: strong, easily worked and beautiful. Its major disadvantage is that current rates of use are unsustainable, leading to widespread deforestation. Natural builders are seeking alternatives to conventional stick-frame construction where wood is used indiscriminately, and have begun to use wood in new ways.
Building with exposed timber-frames surrounded by materials such as straw-clay or straw bales can take advantage of the beauty and structure of wood while eliminating unnecessary use. Innovations in bentwood truss construction in Nova Scotia shows ways to create strong members using smaller diameter trees. Other builders are finding uses for driftwood, and irregularly shaped trees which would otherwise go to waste. Innovative use of scraps and sawdust make the best use of wood for panels, hybrid products, etc. In addition, increased popularity of non-wood construction systems can lead to reduced wood use and ecosystem rehabilitation.
Appropriate timber use is closely tied to sustainable forestry practices. Selective cutting can provide ongoing sources of material while saving delicate ecosystems. Using smaller diameter or unmilled lumber can save large old-growth trees, innovative uses of non-traditional species or young, second growth trees can also be an effective strategy.
Courtesy of Natural Building Resources
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