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Abrazo House

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Guides & tutorials

Ideas and information for people interested in ecological design and construction


Cob is a mixture of clay, sand, fibre (usually straw) and water in controlled amounts, which is used to build with while wet and dries to form an amazingly strong, durable and quite well-insulating building material. It can be used to create walls, floors, arches, shelves, buttresses, domes, sculptures… practically any shape you can imagine, you can build with cob; it’s a bit like making a house out of plasticine. Cob is extremely pleasant and healthy to work with, and encourages creativity. It’s also very flexible and recyclable: just re-wet it and re-work it into a different shape! In fact, it is the world’s most sensual building material.

You can mix cob with your feet, bare or otherwise, but we normally use a rotavator (rototiller) to save time.

Earth, as a building material, is downtrodden and overlooked, yet ubiquitous, free, stable, non-toxic, sensual, and just fun to use. Some people think earth is the building material of the past; we think it’s the material of the future.


One of the most popular and fastest-growing forms of ecological building is the use of straw bales as a wall material — which can be load-bearing (carrying the weight of the roof) or can be used as infill in a wall with a wooden frame to support the roof.

Straw bales are inexpensive and quick to build with (though the finishing work can take longer than with other materials), but their principle advantage over other building materials is their excellent thermal insulation.

But beware of the big bad wolf — as embodied in the forces of wind and water. We have learned from bitter experience that in a climate as damp as ours, it is vital to protect your straw bales from the weather; we had to tear out and rebuild the first story of our house because of damage to the straw bales during an exceptionally wet winter.

Waste treatment

The waste we generate at Abrazo House is mostly dealt with on-site.

Nuestro food and garden waste gets composted or eaten by our chickens. Wood, paper and cardboard are either burnt to heat the house, composted, or used as mulch in the garden

We also deliberately import some waste materials in order to recycle them, such as old beams and windows for building, wood shavings for composting, wine bottles – which formed a translucent bathroom wall, and old car tyres for use in the garden.

We treat all grey water from our sinks, showers and washing machine on site, as well as the human waste from our toilets.

Reciprocal roof

Our first natural building project, Snail Cabin, has a reciprocal frame roof inspired by the spiral of a snail’s shell. This is a type of roof in which three or more beams provide mutual support, avoiding the need for a main beam or central post.

It’s a self-supporting structure, in which each beam rests on the previous one, and the last beam fits underneath the first one. While building it you need to support the first beam temporarily; when the support is removed the whole structure should neatly lock together.

Reciprocal frame roofs are beautiful and strong but rather fiddly to build — especially when it comes to cladding the roof structure with boards. We liked the finished structure so much that we went on to build a smaller reciprocal as a cupola over the top of the first, to make a double reciprocal frame roof.

Solar energy

The main house is designed according to the principles of passive solar design. Where we live, in the northern temperate zone, this means having a well-insulated building with a lot of double-glazed south-facing windows to let in the sun and a large amount of thermal mass to store and release heat, so the house stays at an even temperature day and night, sunny days and cloudy days.

In winter all our supplementary heat comes from a wood burning stove. We burn a mixture of firewood cut from our own trees, leftovers from building projects, and waste wood that we scavenge — all obtained for free. Essentially, we’re still using the sun’s energy, stored in the form of wood.

To heat water for baths, showers and washing up, we do have some solar panels — but not the kind that generate electricity. These are much simpler: they are more like anti-radiators that sit in the sun, heating up. The water that runs through them then circulates (by gravity, no pump required) to a storage tank that sits upstairs in the main house, and stores the hot water ready for use.