Building a Cob Home In Asheville
Building a cob home or structure in Asheville or anywhere else involves using a combination of natural materials, traditional techniques, and modern modifications for comfort and efficiency. Cob is a type of building material made primarily of clay, sand, straw, and water, mixed together to create a moldable, sculptural substance that can be used to form walls, foundations, and even floors. Here's a comprehensive guide on how cob homes are typically constructed, materials used, the history of cob building, and some other essential aspects to consider.
Cob Builders / Resources / Workshops Around Asheville
| Location | Details | Link |
|---|---|---|
| Ashevillage Institute | Features a cob dwelling in its permaculture demonstration site, showcasing natural building techniques. | Ashevillage Institute |
| Earthaven Ecovillage | An eco-village with multiple cob structures, including the 'Leela House' and the Council Hall, demonstrating various natural building methods. | Earthaven Ecovillage |
| This Cob House | Documents the construction of a cob house, providing insights into the building process and materials used. | This Cob House |
| Mud Dauber School | Offers workshops on building with cob and other natural materials, led by experts in the field. | Mud Dauber School |
| Cob Cottage in Murphy | A project where students built a 10-15m² cob cottage, emphasizing hands-on learning in natural construction. | Cob Cottage in Murphy |
Step-by-Step Process of Building a Cob Structure
Site Selection and Preparation:
Choose the site: Cob buildings work best in areas with access to good-quality clay and sand. In Asheville, this might involve selecting land with good soil quality for mixing, as well as a flat area for foundation work.
Excavate for foundation: The first step in cob construction is preparing the foundation. A trench is typically dug for a foundation footing, which might be made of stone, concrete, or recycled materials. This will help prevent moisture from wicking up into the cob walls.
Making Cob Mix:
Gather Materials: Traditional cob is made from three basic ingredients:
Clay: Binds the mix together.
Sand: Gives the cob its structure and prevents cracking.
Straw: Provides tensile strength and helps the cob hold its shape.
Water: Activates the clay and binds the mix together.
Mix the Ingredients: Traditional methods involve stomping barefoot to combine the ingredients in a large pit or on a tarp. For more modern cob builders, a cement mixer or mechanical means may be used.
Building the Walls:
Layering the Cob: The cob mix is applied in thick layers. Builders form small mounds of cob and press them onto the wall structure. Each layer is built on top of the previous one and shaped to create curves and design features. As the walls rise, the cob is sculpted into forms, arches, and niches, with windows and doors cut as the walls cure.
Drying and Curing: The cob must dry between each layer and over several days or weeks to harden completely. Proper drying and curing are crucial to ensure strength and stability.
Roofing and Final Touches:
Construct a Roof: Cob walls are strong but require a solid roof for weather protection. Typically, a wooden frame, often with a thatched roof or other eco-friendly materials, is used. In Asheville, you might see green roofs with vegetation.
Finishing and Insulation: Interior and exterior finishing might involve plastering with lime or clay plaster to give a smooth or textured finish. Insulation materials can be added between walls or in the roof structure.
Materials Used & Where They Likely Came From
Clay: This is the key ingredient, and it is typically gathered locally. Clay is abundant in various parts of the U.S., including areas near Asheville. Clay sources can be tested on-site to ensure they're appropriate for cob construction.
Sand: Like clay, sand is usually sourced from the site or from nearby regions. The right type of sand (often fine, clean sand) is essential to ensuring the strength and texture of the cob.
Straw: Straw is used to reinforce the cob mix. It is generally locally sourced from farms in or near the Asheville area, often from wheat, barley, or oats.
Water: Clean, fresh water from nearby sources is used to mix the cob. The quality of water can influence the consistency of the mix.
Disclaimer:
Cob construction, while environmentally friendly and deeply rooted in history, requires expertise. If you're considering building a cob home or structure, it's crucial to consult with a professional experienced in cob construction to ensure structural integrity and compliance with local building codes. The advice provided here is general and should not be considered a complete guide for actual construction.
The History of Cob Building
Cob construction dates back thousands of years, with evidence of its use in ancient civilizations across Europe, Africa, and the Middle East. In ancient times, cob was used for everything from homes to religious buildings. The technique was especially popular in the UK and parts of the Mediterranean. Cob homes are known for their durability, thermal mass (ability to retain heat), and ability to regulate indoor humidity.
In the U.S., cob construction saw a revival during the late 20th century, particularly in eco-conscious communities. Asheville, with its strong focus on sustainability, is a prime example of a location where cob homes and buildings are gaining popularity.
How Long Do Cob Structures Last?
When properly constructed and maintained, cob structures can last for centuries. Famous examples of ancient cob buildings, such as the mud brick homes of Morocco or the historic cob cottages in the UK, have withstood the test of time. However, cob walls need to be protected from heavy rainfall and moisture, which can degrade the material over time. Proper roofing and periodic maintenance, such as patching cracks and reapplying plaster, can greatly extend the life of a cob structure.
Costs of Building a Cob Home
The cost of building a cob home can vary greatly depending on the location, size, design, and labor involved. On average, the materials themselves can be inexpensive, particularly if clay, sand, and straw are locally sourced. However, labor costs can be significant if you hire skilled professionals. It's also important to factor in the costs of permits, tools, and roofing materials.
The cost of a basic cob house can range from $20,000 to $80,000, depending on size, complexity, and location. This is a rough estimate; in some cases, the cost could be much higher, particularly for larger homes or homes that need custom-built roofing and infrastructure.
Tools Used in Cob Construction
Modern Tools:
Shovels, buckets, and wheelbarrows are commonly used for transporting and mixing the cob.
A cement mixer (for larger projects) can be used to help mix the cob ingredients quickly and thoroughly.
Hand tools such as trowels and carving tools for shaping and detailing the walls.
A plastering tool, usually a wide trowel, is used for smoothing out cob surfaces and adding plaster finishes.
Tools in Ancient Times:
In ancient times, cob builders likely used rudimentary hand tools such as wooden spatulas, sticks, and basic stone or metal tools for mixing and shaping.
The primary tool was the human foot—builders often stomped the clay, sand, and straw mixture to mix it thoroughly before applying it to the walls.
Asheville’s Building Codes in Relation to Cob Structures
Permitting:
Before starting any construction project, whether with cob or traditional materials, a permit is typically required. Asheville follows the North Carolina Building Code, which governs all residential and commercial building projects.
Cob homes, being an alternative building material, may not be explicitly mentioned in the building code. As such, cob structures might need to go through a more rigorous permitting process. The project may need to be reviewed by local authorities or an expert in alternative construction to ensure it meets safety standards.
Compliance with Safety Standards:
Structural Integrity: Cob homes need to be designed and built to handle the local climate, especially considering heavy rain, high humidity, and occasional strong winds. The walls must be stable and capable of supporting the roof and other loads.
Fire Safety: In some cases, fire resistance might be an important consideration. Since cob is a natural, fire-resistant material, it may meet these requirements, but local inspectors might require additional documentation to ensure it passes fire safety codes.
Insulation and Energy Efficiency: Cob provides good thermal mass, helping maintain indoor temperatures. However, building inspectors may require additional insulation for energy efficiency, especially in cold months. Insulation methods might be added to cob homes to meet modern standards.
Historical Preservation and Zoning:
Asheville is home to a rich history of architecture, and in some cases, certain areas may have zoning or historical preservation rules that affect what can be built. This may be relevant when constructing a cob home in or near historically significant districts.
Additionally, zoning codes in Asheville can affect where alternative homes, like cob houses, can be located. For example, a rural zone may be more flexible with construction types, while a residential or urban zone may have stricter building regulations.
Building Codes Specific to Alternative Construction:
North Carolina’s code includes guidelines for alternative and natural building materials, though many of these materials (such as cob) may require special inspection or approval from a licensed architect or engineer to ensure the design is safe.
Some cob builders in Asheville and North Carolina may consult with an engineer who specializes in natural building techniques to verify the integrity of their designs and satisfy building code requirements.
Inspections:
During the construction process, inspections will be required to ensure the project complies with building codes. In cob construction, this might involve periodic checks of wall thickness, foundation integrity, and roof support.
Once construction is completed, a final inspection ensures the home is habitable and safe for occupancy. As cob is a less common material in modern construction, this might take longer and require more paperwork.
How Cob Can Meet Building Codes In Asheville NC
Despite the lack of widespread adoption of cob homes in traditional building codes, cob homes can often meet or exceed most modern building standards. To ensure compliance with building codes, cob builders should:
Work with an architect or engineer: This will help design a home that adheres to local codes, including aspects of structural safety, energy efficiency, fire resistance, and environmental impact.
Submit for approval: Submit the plans to the city’s permitting office for review and approval before construction begins.
Document materials and techniques: Ensure that the materials (e.g., clay, sand, straw) used in the cob mix are well-documented and that the construction methods are clearly outlined.
A Nearby Case Study Of Getting Natural Building Approved In NC
Turtle Island Preserve, a well-known eco-community located in Boone, North Carolina, faced a significant legal challenge related to its alternative building methods, particularly with the use of cob and other natural materials. The conflict centered around zoning regulations and building codes, which initially did not accommodate the unconventional construction methods Turtle Island embraced. However, the community ultimately prevailed in their legal battle, which highlighted both the challenges and successes of using alternative building techniques in a modern regulatory environment.
Background of the Conflict
Turtle Island Preserve was founded by Eddie and Barbara Bowers in the 1980s as an ecological retreat and permaculture farm. The community's main goal was to demonstrate sustainable living practices, which included building homes using natural materials such as cob, straw bale, and earth-friendly construction techniques. This approach was at odds with the traditional building codes and zoning laws of Watauga County, where Boone is located.
In 2003, the county's building department issued a stop-work order on Turtle Island’s projects. This was due to concerns that the structures being built on the land did not comply with local zoning laws, especially in regard to the use of cob as a primary building material. Cob construction, which uses a mixture of clay, sand, and straw, was not recognized in the county’s building codes at the time, and the homes were not built to conventional standards such as fire safety, structural integrity, and energy efficiency.
The Legal Battle
The legal conflict escalated as Turtle Island sought to continue its building practices and preserve its eco-community. The Bowers and their supporters argued that their alternative methods were not only sustainable but also safe and effective, and they emphasized that their structures were designed to work with nature, rather than against it.
The community's supporters included architects, engineers, and sustainability advocates who argued that alternative building methods like cob were both environmentally friendly and structurally sound. They also pointed out that these homes could be built with much lower energy consumption and environmental impact compared to conventional construction methods.
The legal battle was complicated by the local government's resistance to alternative building methods and the difficulty in getting building codes updated to recognize cob and other non-traditional materials. Turtle Island was forced to halt construction and deal with fines, while the community advocated for changes to local building codes to allow for alternative construction.
The Resolution and Victory
In the end, Turtle Island won a significant victory after years of fighting. In 2006, the community reached a settlement with the county that allowed them to continue building with cob and other natural materials, provided they met certain criteria and safety standards. This was a groundbreaking moment for the alternative building community, as it set a precedent for other projects using non-traditional materials.
Key to the settlement was the agreement that Turtle Island would work with engineers to ensure that their homes were structurally sound, energy-efficient, and fire-safe. The community agreed to a more detailed inspection process, including working with experts who could demonstrate the safety and longevity of their methods. In exchange, they were granted the freedom to continue building their eco-friendly homes.
Turtle Island’s success was a combination of legal strategy, expert testimony, and community support. It showed that while alternative building techniques can face significant legal and regulatory hurdles, it is possible to find a middle ground where both traditional building codes and sustainable practices can coexist.
Impact on the Building Community
Turtle Island’s legal victory had broader implications for the use of alternative building materials in North Carolina and across the U.S. It helped set a precedent for other communities and individuals who wished to pursue natural building methods but feared running into legal and zoning issues. The case brought attention to the importance of updating building codes to accommodate sustainable construction techniques, such as cob, straw bale, and earth-sheltered homes.
Additionally, the Turtle Island case inspired many other eco-communities and sustainable living initiatives to push for changes in local building codes, as it demonstrated that advocacy, expert collaboration, and persistence could lead to success.
Conclusion
Turtle Island Preserve's struggle in Boone, NC, over its use of cob and other natural building materials highlights both the challenges and successes of pursuing sustainable, alternative building techniques in a conventional regulatory framework. By working with experts, advocating for change, and engaging in the legal process, Turtle Island was able to preserve its vision for eco-friendly living while complying with local building codes. This victory remains an important milestone for those interested in natural building and sustainable living practices.