Historically, cob has had substantial use in building homes in England, particularly in the South West regions where the required materials are readily available.
Cob houses have appeared in England since at least from the 1200s. Cob’s popularity rose in the late 18th and early 19th centuries as a reaction to the high cost of bricks and the scarce availability of proper quality stones in certain areas. Cob cottages from this time that have been well maintained still stand today, a testament to the durability of the material.
The peculiarity of cob is evidenced by the unique historic building styles in the regions where they were used. This includes the “Cob and Thatch” cottage style, noted for its deep-set windows and doors, and generally rounded vernacular structure.
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What is Cob?
Cob material, the main constituent in cob building, is a mixture of sand, clay, and straw. Sand serves as an aggregate, providing strength and structure. Clay acts as a binder, allowing the material to stick together and hardens when dry.
Straw, on the other hand, adds tensile strength to the mix, preventing it from cracking while simultaneously adding insulation to the building. The general rule of thumb for the mix is 1 part clay, 1-3 parts sand, and straw to taste.
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Cob has some unique properties that make it desirable for building. It is notably fireproof, bug-resistant, and provides excellent insulation against temperature fluctuations, keeping homes warm in winters and cool in summers.
Cob is an environmentally-friendly material because it is abundant and requires little energy to process. It is also biodegradable, reducing the impact on the environment when buildings are eventually demolished.
However, it is essential to note that cob is not without its pitfalls. Chief among these is its low resistance to water, especially in its raw form. Without proper treatment, cob can erode in intense or prolonged periods of wet weather. Though cob structures are durable, they also require regular maintenance to ensure their longevity.
Medieval Origins of Cob Cottages
The exact origins of cob building in England are unclear, but records show that cob houses were being constructed as early as the 13th Century. It’s possible that cob developed from older methods like wattle-and-daub, where a framework of branches was plastered with mud.
One theory suggests that mud initially served as a filler between double wattle walls, and over time, it was discovered that the structures remained intact even after the wattle deteriorated.
Another hypothesis is that cob evolved from the mud mix used in medieval times for binding stone walls and filling cavities between stone layers. When the outer stones were removed or eroded, the durable cob core often remained.
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By the 15th Century, cob houses had become widespread in many parts of Britain, particularly in the Southwest and Wales, where resources like stone and wood were limited, and the subsoil was ideally composed of sandy clay.
Oxen Played Their Part
The typical English cob mixture consisted of clay-based subsoil, straw, water, and occasionally sand or crushed shale or flint. The clay content varied from 3% to 20%, with 5-6% being the most effective proportion. The mixture was prepared either manually, with workers shoveling and stomping, or by having heavy animals like oxen trample it.
The prepared cob was then layered onto a stone foundation using a cob fork and compacted by workers standing on the walls. Each day, a layer or “lift” of cob, ranging from 6 inches to 3 feet in height but typically around 18 inches, was added. This layer would then dry for up to two weeks before the next was applied.
Additional straw was sometimes incorporated into the top of each layer. As the walls dried, they were trimmed back significantly with a paring iron to ensure they were straight and typically measured between 20 and 36 inches thick.
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Cob walls could reach up to 23 feet in height, though they were often shorter. Door and window openings were either integrated during construction or carved out later, using stone or wooden lintels embedded in the wall.
Sir Walter Raleigh
Cob cottages, often constructed by poor tenant farmers and laborers, were a testament to cooperative effort and resourcefulness. With a small team working collectively one day a week, a cob house could be completed within a single season.
A cottage started in spring would typically be ready for its thatch roof and interior whitewash by autumn, allowing its occupants to move in before the onset of winter.
External plastering with lime-sand stucco was often postponed until the following year to ensure the walls had sufficiently dried. Cob outbuildings like barns were sometimes left without plaster.
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However, cob wasn’t exclusively a material for modest homes. Many large townhouses and manors, built from cob before the widespread availability of fired brick, still stand in excellent condition. Notably, Hayes Barton, the birthplace of Sir Walter Raleigh, is one such cob structure.
Raleigh himself had a deep fondness for his childhood home, once offering to purchase it for “whatsoever in your conscience you shall deme it worth.”
In Devon alone, an estimated 20,000 cob homes and an equal number of outbuildings are still in use. A well-constructed cob home could typically last a hundred years without significant repair, highlighting the durability and quality of these traditional structures.
Export of Cob Construction
British emigrants spread the technique of cob construction to various parts of the world, including Australasia and North America. In New Zealand, early settlers found the local clay soil and tussock grass ideal for cob construction, leading to the creation of at least 8,000 cob houses on the South Island, several hundred of which still stand.
In Australia, cob was less common, with mud bricks and rammed earth being the preferred methods of earth building, but a number of cob structures still exist in New South Wales, Queensland, and around Melbourne. In North America, cob buildings from the same period are rare, but they do exist, including a house built in 1836 in Penfield, New York, and a church in Toronto.
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By the end of the last century, cob building in England was seen as outdated and was losing its appeal. However, public perception shifted throughout the 20th century, and now traditional cob cottages with their characteristic thatched roofs are cherished for their historical and aesthetic value.
Due to a near absence of new cob construction in England from World War I until the 1980s, much of the specialized knowledge associated with this craft was lost. Nonetheless, sufficient information remained to spark a revival of cob building in the 1990s, driven largely by historical interest and the real estate appeal of historic cob homes.
The Appeal of Cob Cottages
Cob houses are appealing for several compelling reasons. Firstly, cob walls act as natural insulators. The material absorbs heat, which helps maintain cooler interiors during hot days. At night, as temperatures fall, it releases the stored heat, leading to a stable indoor temperature with minimal fluctuations compared to conventional buildings.
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From a sustainability standpoint, cob is exceptional. The high thermal mass of cob contributes to the energy efficiency of these structures. Its components—earth, water, and straw—are naturally available and often sourced locally, reducing both financial costs and environmental impact.
Furthermore, the absence of synthetic materials in cob construction means it’s free from toxic emissions both during the building process and in its existence thereafter. This eco-friendly aspect extends to the end of a cob structure’s life too; if a cob building is demolished, it does not contribute to environmental pollution.
Possessing a cob house goes beyond merely owning a property; it’s preserving a piece of time-honored heritage.
