What is a Cob House you might ask. Cob construction uses sand, clay and straw, mixed well this special mud is applied to the foundation in continuing layers. Each layer must dry so that it can support the next, and the wall is tapered in as you build up. When it is dry, the walls are very hard and load bearing. The roof is built directly on to the walls, as the walls themselves are the support structure. This technique requires almost no money or skill, and involves very little environmental destruction while at the same time allowing for creative and organic designs which blend into the surroundings.
One Cob House that has caught the public’s attention is that of Architect Féile Butler and her husband Colin Ritchie’s in County Sligo. Having trained with the Cob Cottage Company in 2005, in 2006 they attended the school of Natural Building in Coquille in Oregon which is run by Cob Cottage. Two years later, in 2008 Féile and Colin embarked on building their own 130m2 hybrid cob and timber frame home. The house was completed in 2011 and was built from soil which was excavated on their site and over 80% of the other building materials were salvaged.
Colin Ritchie is a carpenter by trade, having completed his apprenticeship under his father in 1987. Originally from Scotland, he moved to Ireland 1999. He has also worked in Australia and New Zealand. While renovating old stone cottages, he became interested in natural-edged woodwork. He is a true craftsman when it comes to wood. During the construction of the house, Colin made many of the components from scratch: milling up windfall trees to make door frames, door leafs, window boards, stairs, kitchen units; mixing cob and making earth plasters.
Colin built his timber frame workshop first, as a base for the main project. During this time they lived in their 11m x 3.5m (36ft. x 7ft.) mobile home on site, basically a glorified caravan. In January 2008, Mr Ritchie started working on the house and at this stage himself and Féile had added two dogs and a small child to the caravan.
It took a while for Colin and Féile to work out their system. In the beginning, Colin built what he thought it should look like. Féile, being an architect, knew what it should look like and asked Colin to change it. Colin refused and sulked for a few days and told Féile to do it herself. By the third day, Colin had changed it. Féile was once asked how had she managed to have such tight control over the builder. “It’s simple,” she replied, “I’m the wife!” Eventually, Colin figured out that if he asked Féile to look at the task in hand, before he carried it out, everything went much more smoothly. So Féile was called over to the house up to twelve times a day. It’s handy when the architct lives on site. And when she could, when the baby decided to act like all those other natural building kids, she helped a little bit with the build too.
The winter of 2009 was pretty grim, the caravan was on its last legs. Colin and Féile thought they may be ready to move in for the arrival of baby number two , due in the summer of 2010. But almost-single-handedly-built-houses have a habit of taking longer that you’d expect so baby number two and the caravan was not only bursting at the seams but it was literally disintergrating.
As Autumn 2010 set in, Colin and Féile and the two children and the two dogs waited for their mud floor to dry. They waited and they waited and they waited. At last, they could wait no more. So with a slightly sticky sensation underfoot, they left the caravan and, joy of joys, moved into their new home. The floor around the dining table is pocked with chair-leg dents, the price of moving in before the floor was fully hard. Colin says it adds character.
They tried to give away the caravan, for free. Nobody wanted it. Colin stripped it of all its re-usable and recyclable components. In the spring of 2011, with his son on his knee, Colin broke up what remained of the caravan with a very large digger after living in it for six and a half years.
Cob allows itself to be shaped and moulded while you build, allowing shelves, alcoves and even furniture to be built right into the walls. Cob being earth, is totally fireproof, so even a fireplace can be built into the design. Regular working windows and doors are embedded in the cob along with their lentils while you build the layers up. If you want a fixed window you can use any kind of glass embedded directly into the cob. This allows for using broken windows (you cob over the broken part) or creative things such as glass bottles or a car windshield.
As cob walls are between 1 and 2 feet thick they are nice and warm. The cob has a high thermal mass which allows it to absorb the sun’s energy during the day to keep the interior cool and radiate the energy back at night to keep the interior warm. In this way cob acts as a temperature regulator. A cob house needs very little additional heating in winter.
The word Cob comes from an Old English root meaning ‘a lump or rounded mass.’ It’s a traditional building technique using hand formed lumps of earth mixed with sand and straw which is easy to learn and inexpensive to build. When the cob hardens it is similar to lean concrete and it is used like adobe to create self supporting, load bearing walls. It has been used for centuries throughout Western Europe as far North as the latitude of Alaska, even in rainy and windy climates.
This ancient technology doesn’t contribute to deforestation, pollution or mining, nor depend on manufactured materials or power tools. Cob is nontoxic and completely recyclable, which is important in this era of environmental degradation, dwindling natural resources and chemical contaminants.
Cob is one of many methods for building with raw earth, the world’s commonest construction material. It surpasses related techniques such as adobe, rammed earth pise, and compressed earth bricks both in ease of construction and freedom of design.
Unlike its counterpart adobe, cob can be built in cool damp climates that Irish home owners are accustomed to. Since you don’t need straight forms or rectilinear molds, cob lends itself to organic shapes: curved walls, arches and vaults. Building with cob is a sensory and aesthetic experience like sculpting with clay. You can add on, cut out, or reshape at any time, even after the cob is dry.
Cob is very resistant to weathering. Because of its porous nature, it withstands long periods of rain without weakening. However, too much exposure is best avoided by the “boots and cap” strategy: wide roof eaves to protect the walls and an impervious foundation. In windy areas a lime-sand plaster is traditionally used to protect exterior cob walls.
Cob is earth used as a building material. Straw is mixed in with it to improve its strength. If your soil is too sandy, you add a little clay. If your soil has too much clay in it, you add a little sand. If you are lucky, your earth may be just right. This is ‘ready-mix’.
From an environmentally-friendly point of view, it does not get much better. You source your raw material yourself, right where you want to build. No tree is cut down, no rock is quarried, no metal is mined, no oil is extracted. The raw material does not require any melting or heating at high temperatures, or the addition of any chemicals or massive quantities of water, to turn it into a building material.
In generations to come, if your home is no longer occupied, cob will eventually disintegrate back into the earth and it will leave no trace. At the end of the day, a cob home should not cost any more than a standard-built house. It is possible to build it cheaper than a standard house. A curved cob wall is actually stronger than a straight one, as it becomes self-buttressing; it supports itself. This opens up so many possibilities for a completely individual building, full of personality and free from the 1.2m x 2.4 (4ft. x 8ft.) module dictated by so many modern building materials.
Cob buildings are built as monoliths – huge, thick, solid walls. Traditionally they were built approximately 600mm (2 ft.) wide, up to a storey-and-a-half or more.
They need ‘a good hat and good boots’, large overhangs and stone or block plinths to minimise the amount of rain reaching the cob walls. They need to be finished with compatible materials, which will protect the cob but also allow it to breathe.
If you maintain your cob building well, such as renewing your external limewash every few years, it will last for generations.
Cob does not have a ‘good’ u-value. The current building regulations in Ireland require that the maximum u-value for a wall should be 0.21 W/m²K. A 600mm wide cob wall will only achieve values from approxiamtely 0.4 to 0.65 W/m²K, pretty far off the mark. This implies that cob walls need to be heavily insulated to achieve current standards of thermal comfort.
In Ireland, there is a long tradition of earthen buildings, although most people don’t realise it. If the cob walls are well maintained and the plaster is still intact, most people assume the building is stone. They have no idea that they may be living in a ‘mud hut’.