A self-builder develops a specialism in earth building

This project demonstrates another low-embodied- energy, heavyweight, alternative method of construction, with a long pedigree in parts of Britain. Here earth is used to build a modern but very sculptural house.

A self-builder discovers cob

Born and brought up in east Devon, Kevin McCabe returned to the area after living a few years in London. He was working as a jobbing builder laying patios and building extensions, and got a job working on the renovation of a farmhouse listed as of architectural and historic interest. The project was grant-aided by English Heritage, who required the foreman on the job to be qualified in the use of lime in building – for mortar, render, plaster and paint. Kevin went on a one-day course organized by the Society for the Protection of Ancient Buildings (SPAB), which is the largest, oldest and most technically expert pressure group fighting to save old buildings from decay, demolition and damage: the SPAB represents a practical and positive side of conservation. Amongst other things, Kevin was responsible for rebuilding a cob wall as part of the farmhouse refurbishment. Cob is the form of earth building which used to be the principal form of construction in parts of Devon. There are estimated to be around 20,000 cob houses still in use in the county, although the building technique has fallen into disuse over the last 200 years or so. Earth mixed with straw is built up in layers around half-a-metre high to form walls around 600 to 900mm thick, which are left to dry for a couple of weeks and then trimmed to form slightly tapered walls, which are then lime-rendered on the inside and outside.

Kevin went on a course organized by the Devon Rural Skills Trust, given by a 70-year-old who had learned the techniques of building in cob from his parents. Kevin rebuilt the wall, and found the work easy and very satisfying. Kevin is a serial self-builder, and has made a career of building or renovating houses. His fourth was a virtually derelict stone barn with planning permission for an extension in stone. Although Kevin could have used stone, in the light of his recent experience of cob construction, he decided to reapply for planning permission for the work to be carried out in cob – and so started a new business as ‘The Cob Specialist’, persuading planners and potential customers that building in traditional cob is not only possible but also a good idea. This has led to a series of cob-built extensions and new houses over the last ten years or so.

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Balancing moisture

Earth building is a very low-embodied-energy way of building, and avoids the use of energy associated with the production of fired clay bricks and Portland cement, which is now one of the principal sources of greenhouse gas production. It is a method of building with a very high thermal capacity; it takes a long time to heat up the building, but stores a significant amount of heat within the structure, which creates stable comfortable conditions in winter because the radiant temperature of the walls is relatively high, and in summer the building remains cool inside during hot weather. Kevin is of the view that a cob house is particularly comfortable to live in because it maintains a humidity level slightly higher than conventional construction. Like Ralph Carpenter describing living in his hemp house, Kevin emphasizes the role of the balance of moisture in the building to explain the thermal performance of the construction in the face of the theoretically poor thermal insulation of the walls – a U-value of 0.45 W/m2 °C for the thick walls of cob with no additional insulation.

Thermal performance

Kevin’s own house, completed three years ago, is designed to achieve the maximum Standard Assessment Procedure (SAP) rating possible at the time: 120. (The energy performance of buildings has been changed with the amendment of the Building Regulations that came into force in April 2006. The SAP is based on the energy cost of heating a house, now on a scale of 1 to 100, but the thermal performance is now linked to the CO2 emissions produced to accord with European Union directives.) Kevin’s house achieves this high rating by incorporating high levels of insulation in the floor (100mm polystyrene below the screed which incorporates the underfloor heating) and 125mm mineral wool slabs below the thatched roof. The thatched roof provides the deep overhang necessary to protect the walls, and a plinth of local stone protects the base of the wall by lifting the earth above the splash zone and incorporating a damp- proof course. The stone is backed by a highly insulated construction consisting of two skins of aircrete blocks with 300mm of polystyrene insulation between. The house has an 11 kW oil- fired condensing boiler driving underfloor heating to the ground floor and providing domestic hot water. The three bathrooms on the first floor are provided with a heated towel rail. The top floor was built without any heating, in the expectation that the combination of warm air rising from below coupled with the high level of insulation in the roof would provide comfortable conditions. However, it has proved uncomfortably chilly on a cold night; the suggestion is that the thatch lets the cold north wind through and so a hole was made through the cob to duct warm air from above the log fire in the living- room but this proved insufficient and so a radiator has been added to the heating system. Cooking is by oil-fired Aga, and a large open fireplace in the living room has a log fire most evenings in winter.

A modern cob house

The house occupies a site with magnificent views. Kevin built the house for sale, but decided to move in with his family when it was finished. He designed the house himself, with help from an architect – who was ‘not too headstrong’, as he puts it – and the structure was calculated by a structural engineer. The 340m2 house is planned on three split-level floors linked by two spiral staircases made of solid cob winding around the solid cob flue. Kevin was able to avoid fitting fire doors to the staircase and create an open plan feel to the interior because the Building Control officer agreed that it was not necessary, as the top inhabited level was less than 4.5 metres above the highest ground level. All the internal walls are cob, creating a massive thermal capacity. There is a cob- built larder in the kitchen ventilated to the outside, which keeps food cool, but not too cold – spreadable butter, for instance. Although built in a traditional manner, the house is very light and sunny and modern in feel. The interior is very colourful, with lime wash on a lime skim coat on earth plaster on the raw cob walls. There are no straight walls, and the interior is very sculptural. The exterior is raw cob at present, a deep red in colour with the texture of straw and stones showing through, but Kevin intends to apply a lime render in the traditional manner.

Local materials

Materials from the immediate locality are used as far as possible: earth from the field outside with a clay content of around 20%, but with straw and some coarse sand and 20mm-diameter stone added to control shrinkage. For cob building, the earth can have a clay content of between 10% and 30%, and about half the soil in the surrounding area and in the county of Devon is suitable. The upper floors are timber, on joists on green oak beams with pegged joints. The green oak lintels to the inside of the window openings have shrunk as the timber has dried out and created gaps which surprisingly have led to substantial air infiltration through the three-feet-thick walls. Oak is used for doors and door frames – local oak where possible – and imported plantation-grown material from France where long, straight and knot- free material is required. Local chestnut is used for the windows. This is very similar to oak; although a little more expensive, it generates far less waste as there is much less sapwood, which is not durable. Chestnut is more stable and not as hard, which means that it can be worked more easily. However, as he says, Kevin is not ‘religious’ about the specification: the ground floor has Italian porcelain tiles, which look terrific.

A cob building business

Kevin just can’t stop cob building, and has completed a three-storey music room, studio and cider house annexe, a workshop-cum-barn and a cob pizza oven. A domed sauna building is under construction. He is building a similar house for sale nearby which incorporates a number of improvements. Firstly, there is an enclosure around the spiral staircase to the top floor to improve the sound separation. The living-room is separated from the stair for the same reason, and the underfloor heating will extend to the shower rooms to make it comfortable on the feet. Cob is not a particularly cheap way of building, and probably costs slightly more than a conventional brick and block cavity wall – whilst the material may cost little or nothing, it is a labour-intensive process to mix it, place it and trim it to form walls, and the building season is limited to between March and September. This new house will cost around £250,000 to build, for a 250m2 building. It is, however, a very low-energy way of building and creates comfortable buildings with high thermal mass – and very appealing sculptural forms. The planning authorities in this part of Devon have been supportive of a sustainable approach to building which is a development of the local vernacular, and there is a market for his high-quality, low-energy houses.

Top left: The next house under construction.

Bottom left: Straw, coarse sand and stones are added to earth from the field to limit shrinkage. This wall will he finished off with a lime render.

Sustainability should become an essential ingredient of design

A large part of the business of sustainable or ecological design is about designing buildings properly: designing for real needs, in a proper relationship with the climate and surroundings, and constructed of quality materials. This means creating buildings that are useful and long-lasting, that can be adapted to changing needs and expectations, that are loved and cared for – not to forget minimizing harmful impacts on the environment.

It is crucially important that environmental issues are considered right from the start: it is no good merely adding technical fixes as you go along – which will cost more, and will never be satisfactory. If an environmental strategy is in place from the start, your building should have a much enhanced performance at little or no extra cost. We must get to the point where green issues are as much part of designing buildings as considering the structure or safety in case of fire – in the same way that it is automatic that fire safety is considered throughout the building process.

You may very likely be employing an architect to help with the designing and obtaining the necessary permissions, and it is vitally important that he or she understands your aims and has the experience necessary to put them into practice. Ways of ensuring that the people that you employ will be able to realize your vision are discussed in the next chapter.

The process of design

The process of design is complex and difficult to define, but can be summarized as considering the many factors that a building has to take into account – practical needs, aesthetic judgements, personal preferences, costs, regulations, environmental impacts, structural adequacy, comfort – and manipulating them until they are in proper balance.

This process proceeds from the general to the particular, just as the patterns of the Pattern Language do.

Each aspect is considered in turn in the most general terms, and an initial synthesis is made which defines the overall limits of the project. With the broad outlines established, you will move on to give some definition to the outlines, to begin to quantify sizes and costs to the point of having an initial design. It is an iterative process, with more information and detail added at each turn of the circle. The next iteration will define matters such as the materials to be used, and will be firm and detailed enough to obtain a planning permission. Another turn of the circle will provide more detail on the structure, for example, and provide enough detail about the construction for Building Regulations approval to be sought. This will then form the basis for detailed orders for materials and components which define the size, specification and colour of the parts of the building. The design process continues throughout the construction period, with detailed decisions being made from day to day about how parts join together and what equipment to order, for instance. Conventionally the builder makes many of these decisions – sometimes consulting you first and sometimes doing what he thinks best, sometimes making the right choice and sometimes not.

As a general pattern emerges, opportunities are revealed for the next range of decisions, which when taken allow yet further developments to flow from them. It is an organic process and does not rely on the ability to conceive an entire, perfect concept at the outset.

Designing a green building

What differentiates the design process for a green building from any other is that the issues of siting, house layout, construction, structure, materials specification, heating, ventilation, landscaping and so on are all looked at from the perspective of reducing energy consumption, emissions, water consumption and waste, avoiding threats to health and allowing for adaptability in addition to the conventional aspects of cost, appearance, strength and so on. These issues have to be assessed at all stages – it is no good if, after your taking care to specify a certain detail or product, a contractor or subcontractor goes down the road and buys something else which is not environmentally sustainable because it’s easier or cheaper.

This adds yet another layer of concern to the already complex process of design. It is also necessary to take care over design and specification, because standard tried and tested solutions are often not available, and low-environmental-impact buildings may have additional systems to design for water recycling, rainwater harvesting, wind generation or solar power.

The initial idea

The first idea may be no more than an estimate of the size of the building and a scribbled diagram showing how it might fit on the site, considering its shape, slope, outlook and access. Consider orientation, which will affect the degree of passive solar gains that you will be able to make use of. This initial analysis may have to be applied a number of times to different sites as the process of site acquisition proceeds. At the outset you will have to consider what the main aims of the project are – how important is cost, and how much you want to spend; what is your feeling about appearance (modern or traditional); whether you have a preference for a particular way of building (e.g. in timber, because it has a warm appearance or because it is relatively easy to work with hammer and saw). Visit completed buildings, and measure rooms which you are familiar with when planning the house.

Developing the diagram

Once there is some certainty about the site and the budget, diagrams can be refined to show the spaces required and how they relate to one another. What goes upstairs and what downstairs, how the inside spaces relate to outside spaces, where should the windows go, whether there should be balconies, a patio, a veranda, where are the views and existing trees. You should make an initial assessment of the environmental strategy concerning siting, layout, materials, energy, heating, hot water, ventilation and renewable energy. You will have to consider the basic choices for the structural system and form of construction. Finally, you must make an estimate of the cost of this preliminary design.

Adding the detail

This can now be elaborated by revisiting these issues and firming them up, adding dimensions, making a preliminary layout for critical areas such as kitchen and bathroom so that you can allocate the right amount of space, and then accurately plotting the building on the site, checking overlooking and the relationship of the inside to the outside, considering new dimensions to the building – what will it look like in elevation, what materials, where are the openings. Consider the building in section to create volumes, not just spaces; stairs, galleries, doubleheight rooms and so on. Consider the structural alternatives in more detail and make choices for the construction of the floors, roofs and walls. Make initial choices for materials, particularly where they affect the appearance of the building, which will be a matter of interest to the planning authority; and for the heating and other systems in the building. Check the Building Regulations for the rules for Means of Escape in case of fire, energy performance, and other requirements. Pull all this lot together and check the cost estimate again.

Submitting a planning application

Once you are satisfied that the design achieves your objectives – provides the necessary accommodation in rooms that are delightful, light with good views and that the building has the required energy and environmental performance, relates to the site and its surroundings, meets the Building Regulations, can be built for the budget, looks great and possesses that quality without a name – then accurate drawings can be prepared and a planning application submitted. You may wish to refer to one of the other books around which give good advice on how to obtain planning permission.

The Building Regulations

Once a planning permission is obtained you will have to develop the design in more detail to show how it is constructed, to calculate the structure and energy performance, and to show how it complies with the Building Regulations. Detailed drawings will show how the main elements (the roof, walls and floors) are constructed, how they meet at the main junctions at the eaves and so on, and also how the special details where a roof abuts a wall or where a floor changes level are to be carried out. Everything now needs a dimension so that it can be built. You will need to obtain the technical details of materials, components and equipment, and assess their performance from an environmental point of view as well as the usual issues of strength, maintenance, cost and so on. Visit the showroom when deciding on bathroom fittings and so on. You will be obtaining quotations for alternative products and specifications and checking the cost again.

You will now be deciding who will be carrying out the building work – if you are planning to carry out most or some of the work yourself, employ subcontractors directly for each stage of the work, or get a general contractor to carry out all or most of the work. The issue here is that most contractors and subcontractors are not familiar with the issues involved in green construction. There is no point in specifying an airtightness membrane, for example, if the builder does not understand its purpose and how to install it and make the joints airtight. Employing a builder is discussed in the next chapter.

Designing has not stopped by this stage, because there will still probably be details of bathroom and kitchen layouts, boilers and ventilation systems, finishes and colours that need to be decided. In some ways, if you are employing a builder it is desirable that as many decisions as possible can be made before starting building, because this makes the time and cost more certain. However, there are real advantages in leaving things until as late as possible so that you can see things in situ and make decisions with the building in front of you. This really only works if you are in full control of the process and if you are aware of the lead-in times from placing an order to materials arriving on site.

What is it that makes buildings survive well?

An important aspect of designing sustainable buildings which have a long-term future is to make adaptable to suit people’s changing needs and aspirations, and ways of achieving this are discussed in Chapter 6 on building for longevity. Another essential ingredient is for buildings to remain wanted. They must be loved and cherished, for then they will be looked after, defended, changed and improved over the years. So green buildings need to remain useful – but what is it that will make them cherished and loved? Is there a special quality that makes a good building, and does it make some buildings survive while others are disposed of before their time?

The quality without a name

Christopher Alexander is an architect, teacher, thinker and writer who has developed a way of thinking about such a quality that makes places cared for, and makes them come to life. Although often ‘we know what we like’, we have not much exercised our minds as to why we like it. We may respond with pleasure to an old Cotswold village street with a great timber-framed barn, or a tile- hung cottage sheltering beside a copse, but we cannot put our finger on precisely what quality it is that moves us so. Alexander says: “It is easy to understand why people believe so firmly that there is no single, solid basis for the difference between good building and bad. It happens because the single central quality that makes the difference cannot be named.” In his book The Timeless Way of Building he devotes himself to identifying that nameless quality, and at the end we realize that we knew all along what it was but were afraid to say so in case we seemed foolish in the eyes of the experts.

A Pattern Language

Having grasped the nature of the quality without a name, it is another thing to devise buildings that encompass it. Alexander and his team spent years researching and tabulating the universally recognized features that are common to the buildings we love. They uncovered a language of patterns from which these places were assembled. For instance, of one pattern, ‘Light on Two Sides of Every Room’ (number 159 in his book), which he claims “perhaps more than any other single pattern determines the success or failure of a room”, he says: “Almost everyone has some experience of a room filled with light, sun streaming in, perhaps yellow curtains, white wood, patches of sunlight on the floor, which the cat searches for – soft cushions where the light is, a garden full of flowers to look out onto.”

His next book, A Pattern Language, identifies and lovingly describes 253 such patterns (to be going on with, as it were, because the language grows as you use it and more patterns suggest themselves – it is an open way of thinking, not a closed system). Every time Alexander identifies a place that lives and takes us to the patterns that went into it, we recognize it. “If you can search your own experience,” he says, “you can certainly remember a place like this – so beautiful it takes your breath away to think of it.”

These patterns are the building-blocks that go to make the rooms, buildings, places, towns and cities around us. They make explicit those invariant features and attributes of places and buildings that work well and which we like, often without being able to articulate why. These patterns can be used to create an infinite range of examples, all different but all sharing those essential features that make them function well. A pattern language gives each person who uses it the power to create an infinite variety of new and unique places, just as everyday language gives a person the power to create an infinite variety of sentences.

Finding our own pattern language

In some form, every person has a dream to make a living world, a universe: whoever you are, you may have the dream of one day building a beautiful house for your family, a garden, a fountain, a fishpond, a big room with soft light, flowers outside and the smell of new grass. Alexander invites us to employ a pattern language whenever we aspire to build: “You can use it to work with your neighbours, to improve your town and neighbourhood. You can use it to design a house, for yourself, with your family …”

I commend these two books to you warmly as they are truly enlightening: The Timeless Way of Building for insights, and A Pattern Language as a practical reference book to help you make the right decisions in sequence, going from the general to the particular, from the broad sweep to the fine detail.

An example of the Pattern Language in action

Brian Richardson, former colleague and co-author with me of the original Self-Build Book published in 1991, recalls the design process that he and Maureen went through for their house in Herefordshire.

The Alexander books are a wonderful way of ordering your thoughts and deepening your insights, but are not a set of formulae that will of themselves produce design solutions. Having considered the appropriate patterns, you still do the actual designing yourself. Your decisions will come out of your own experience: Alexander helps you to recognize things you find you already know.

The books are delightful reading and easy to comprehend. The pattern language has the structure of a network – each pattern connects to the one around it. As you move through it you select appropriate patterns and develop them for your particular situation.

With the overall concept of the project delineated this way, construction can be embarked upon with confidence. As the building takes shape and work progresses, adjustments can be made by the self-builder to take into account unforeseen factors. This is in contrast with the orthodox architect-supervised building contract where the design is frozen at the moment the documents are signed and any subsequent variation provides excuse for a practically unstaunchable financial haemorrhage. The job thought out in the ‘Timeless Way’ can be a happy blend of careful planning and last-minute improvisation. True freedom!

To demonstrate its application, this is a brief selection from the range of patterns that Brian applied to his self-built environment in Herefordshire. He gives the name and number, and quotes the core description of the patterns used (not necessarily in Alexander’s sequence), and then describes how he expressed it.

Old Age Cottage

Old people, especially when they are alone, face a terrible dilemma. On the one hand, there are inescapable forces pushing them towards independence: their children move away; the neighbourhood changes; their friends and wives and husbands die. On the other hand, by the very nature of ageing, old people become dependent on simple conveniences, simple connections to the society about them. . . . Build small cottages specifically for old people. Build some of them on the land of larger houses, for a grandparent. . . .

In our particular circumstances, this pattern took a slightly different form. The ‘small cottage’ was already occupied by my widowed mother, and became a suitable habitation for an old person by our building the family home adjoining it. It was to our mutual advantage. She would be looked after in her old age and be able to stay in her own wellloved, cosy surroundings instead of going into a ‘home’. We would have a superb building site with space, sun, a view and fertile land.

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