“It will come again the building of cottages that are knit intimately to their sites and surroundings as of old, cottages consanguineous with the ground they stand on.” – Clough Williams-Ellis
What is cob building?
Cob is an ancient earth building technique using a combination of clayey subsoil, sand, straw and water. These materials are mixed together either manually, by stomping or dancing on the mix on tarpaulins, or with machinery. The mix is then formed into lumps or cobs and compressed together to form the walls of a building. The mix can also be compressed in moveable wooden forms into wet blocks, which are integrated into the wall. This is known as ‘box cob’. The cob building process is rather like building a giant clay pot.
Cob has been used for centuries by many cultures worldwide. Yemen is particularly famous for its cob buildings – with 14-storey examples that have existed in seismically-active areas for hundreds of years. In the UK, there are many thousands of old, still occupied cob buildings – especially in the South-West, Scotland, parts of East Anglia and Wales – some over 400 or even 500 years old.
The Industrial Revolution marked a move to the use of more standardised products and materials, and thus more local, natural building materials were abandoned. There has been a recent resurgence in cob building however, especially along the west coast of the US, due to over-logging and the need to reduce the amount of timber used in builds – but also because of its novelty, and the popularity of its durable and sustainable nature.
Adobe or mud-brick building uses a cob mix to make bricks that are dried in the sun before being used for building. Adobe is a traditonal building method in the south-west USA and Mexico.
What are the benefits of cob building?
Cob is arguably the most environmentally-friendly building material there is, because:
- around a third of the world’s land mass contains soil suitable for cob building, which means that the material can usually be found on or near to the building site – the costs and emissions associated with the processing and transport of bulk materials is reduced or eliminated;
- reclaimed materials and products can easily be incorporated into the design – cob can be moulded around them;
- typically uses 60% less timber than a stud-frame house;
- the flexibility and fluidity of a cob build allows for curvilinear (yes, it is a word) shapes which enclose space more efficiently, reducing the size of building required for a specific use;
- cob is biodegradable – abandon cob walls and they will become incorporated back into nature without a trace very quickly;
- cob has very low embodied energy, is non-toxic, and can be recycled;
- as cob is breathable and flexible, it works well with other natural materials such as timber, stone, straw bales, slate, thatch, lime etc, as part of a natural home.
- Your building material is free (although you’ll need a digger to get it out of the ground and dumped next to your proposed building); however, a cob building will only be cheaper than a conventional building if you do it yourself, as it’s very labour intensive.
- High thermal mass and good humidity regulation results in stable temperatures and good air quality.
- Airtightness in houses is costly to achieve, and has contributed to the huge rise in cases of asthma in children over the last 50 years; a cob house is more eco-friendly than an airtight one – keep it small, build with natural, local materials and heat it with passive solar and wood.
- It’s a fun and creative building method – the nature of the material and the sculptural / mud-pie style of building is inclusive, and can bring together people with diverse backgrounds and abilities who can work together as part of a team.
- Cob has compressive and tensile strength, so your building will be very solid – but it’s flexible, and so won’t crack if there’s any movement.
- It’s easy to repair – just patch it with more cob.
- Cob buildings are beautiful and unique – they’re ‘of the earth’ and have a feel that a bricks and mortar building can never achieve.
What can I do?
See resources: you can go on a practical course to introduce yourself to the material and the techniques to see if it is the right choice for you; and you can buy a book to get a bit more background information. Then, off you go. Here are a few things to think about.
Planning and building regulations
Planning permission is sought in the same way as for more conventional housing. Problems may be encountered around location of the building, access, design and finishes, not specifically with the building material itself. The government are supposed to be promoting sustainable development, which could work in your favour.
Building Regulations compliance shouldn’t be a problem provided the officer is given sufficient detail to make an accurate assessment. Don’t be vague – give them as much detail as you can; impress them. New cob structures with full building regs approval include the RIBA-award-winning ‘Cobtun’ house and Kevin McCabe’s house at Keppel Gate in Devon. See here for more information about building regs and planning permission related to cob.
When considering a cob build, ensure access to water, and suitable clayey subsoil on site or in the local vicinity. It’s also important to consider access onto your site due to the heavy nature of the materials, especially in relation to the precise location of your building – you don’t want to be wheelbarrowing all your materials uphill. If you’re in a flood plain, then maybe cob isn’t the best option, and maybe you could consider something more appropriate (but just as natural), such as round wood timber frame.
Cob building is labour-intensive and seasonally-dependent (Apr-Nov for the cob part of the build), so start with a small design that can be added to at a later date. This will give you more confidence with the material, and allow you to learn from your mistakes before moving on to a larger structure.
Cob always needs a good ‘hat and boots’ – i.e. solid, dry foundations, and a roof with a good overhang (at least 30cm). Foundations can be a rubble and gravel-filled trench with a perforated land drain to a soakaway to remove excess water.
Cob walls can take driving rain, as long as they have a chance to dry out. The outer walls can have a layer of lime render for protection, or an earth plaster that is re-applied every few years. Earth plaster is a finer version of the cob – sieved earth, finely-chopped straw, plastering sand and flour paste (which acts as a plasticiser and improves flexibility). Cement renders must never be used, as they destroy breathability and flexibility.
Cob doesn’t have good insulation properties, but to compensate, it has good thermal mass. Foundations can be insulated with pumice or vermiculite mixed with clay slip and rammed into cavities in the foundations. Floors can also be insulated with vermiculite, and ceilings can be insulated with recycled newspaper or sheep’s wool insulation.
Thanks to Annabel Cameron-Duff of the Roundhouse Company (formerly Earthed) for information and Linda Royles of Cob in the Community for the main photograph
Whilst you’re here, why not take a look at the other 30+ shelter topics available? And don’t forget to visit our main topics page to explore over 200 aspects of low-impact living and our homepage to learn more about why we do what we do.
The specialist(s) below will respond to queries on this topic. Please comment in the box at the bottom of the page.
Annabel and Alan Cameron-Duff discovered the joys of building with cob on a natural building apprenticeship in the States in 2001. Inspired by the flexible and sculptural nature of building with earth and the inclusive and community spirit it imparted, they returned home to set up ‘Earthed’ in 2003, and in 2015, the Roundhouse Company was born.
The views expressed here are those of the author and not necessarily lowimpact.org's
1Charlotte Eve March 14th, 2016
If you are interested in learning to build your own cob house or cob garden studio check out the cob building courses at http://www.cobcourses.com They are run by Kate Edwards from her own award winning self-built cob house in Norfolk. The course is an excellent mix of theory and hands-on learning, designed to give you all the skills you need to go away and start your building project at the end of the course.
2gailhart June 23rd, 2016
COB BUILDING WORKSHOP IN SOUTHERN PORTUGAL from the 11th July – 21st July 2016. Come and enjoy the sun and the simple nature of the Alentejo region of Portugal. You can do a minimum of 3 days. The cost is 60€ per day to include all food, camping and the workshop. The workshop is being led by Veronica Balfour Paul. Please contact me for more details [email protected]. Gail
3Rhonda Ann Godwin October 20th, 2016
Am remembering how I nearly froze to death in Scotland the winter of 75 and so hoping (any thoughts, advice) the climate in Saskatchewan Canada is suitable for cob building. Occasionally our temperatures drop to minus 30 degrees Celcius now (was much colder 50 years ago). Thanks.
4Jan sexon February 21st, 2017
You talk about wool insulation as far as I have heard, it has a big down side, the moth. It eats it and leaves a dust behind
5gail February 21st, 2017
well we have had ours in the floor and ceiling for 12 years +/-. no probs it was dusted with lime which should help and the wool needs to be ‘raw’ is in with all the lanolin left it. a friend of mine who has built her own cob house put the wool in feed sacks and piled them up all over the ceiling.
6cobinthecommunity January 12th, 2018
2018 brings a whole host of clay, creative and community focussed activities that, London based Cob in the Community CIC would like to see happening over the next 3 years from our brand new base in the heart of Finsbury Park, N4:
? Portable cob oven build – for communities / voluntary groups
? Cob oven – train the trainer / CIC Mud Mason apprentice
? Low impact building, cob and #permaculture
? Politics of mud and mindfulness
? Clay renders workshop
? Medieval mud beehives (skeps)
? Plastic bottles and earth construction
? Live build (outdoor classroom)
? How to repair, improve and get more out of your cob / clay oven
? Cob and enterprise – working to feed and provide employment for hard to reach vulnerable people and marginalised communities
We especially want to hear from
a) Groups wanting clay based structures such as ovens or buildings
b) Skill swap with individuals wanting to learn about cob in exchange for admin, marketing, fundraising or project management
c) Partnerships with sympathetic organisations, visionary thinkers, creative groups and those wanting to collaborate and strategically make the world a better place.
7adrian March 16th, 2018
Hi Chaps, Adrian here (roundwood guy, wholewoods) we met years ago during the lili shows at the grand designs exhibitions. Anyway one of our builds for an educational charity has subsequently had some cordwood and also wattle and daub walls put in which are starting to get some blown-in rain damage. The charity are looking for the cheapest solution for weather protecting those walls. They are asking is there a cheaper solution rather than using lime. Is there anything you’d recommend or does it have to be lime? I hope that life is treating you well and that our paths cross again some day. xx
8Annabel Cameron-Duff March 21st, 2018
Hi Adrian, good to hear from you. How funny, we were just talking about getting in touch with you about an oak shingle roof. Hope you are well. You could use an earth plaster and when this is dry apply a few coats of linseed oil and beeswax or a litema (cow dung/clay coat). However, I would really recommend applying a lime plaster as this will last longer and although more expensive in the short term for materials it won’t have to be re-applied a few years down the line which the earth most likely will have to (depending on how exposed the walls are). The other quicker option is applying a few coats of lime wash and then reapplying a new coat each year ( it will still have to be protected with hessian like a lime plaster though during the initial carbonation process). I’ll send you an email re the roof through your website. Best wishes xo
9fiona McGeough May 3rd, 2018
I have purchased a grade 2 listed cob house near Aberystwyth and I am looking for some help with renovation and saving the oldest house in the village.
I understand you do sustainable work with cob and wonder if you have any contacts that could help me?
Thank you for your time
10Annabel Cameron-Duff May 13th, 2018
We would be happy to discuss your build in more detail. If you would like to get in touch with us by email theroundho[email protected] we can either help you ourselves or point you in the right direction of others who can help. Do you have an architect on board with plans for the renovation of the build, a budget in mind, a time frame of when you are looking to get the work done?
11Lua July 24th, 2018
What would it take to have an instructor go to a rural farming village near Kampala, Uganda and teach/supervise the construction of some cob houses? There would be plenty of people to help.
12Annabel Cameron-Duff July 31st, 2018
We would be happy to discuss your project in more detail. If you would like to get in touch with us by email [email protected] we can either help you ourselves or point you in the right direction of others who can help. Do you have funding in mind to cover the project as you would need to be able to cover things like travel expenses, materials, training fees, design fees? Do you have designs in place for the builds or are you looking for someone to also design the cob houses? This is something we could also provide. Do you have a time frame in mind, when would you be looking to start and complete the project? How many cob houses? We could train up a core team of people for one build and they could then go on to continue building the others with support from us via email and skype.
We look forward to hearing from you.
13Paul Peche November 2nd, 2018
We have a field in West Wiltshire and wanted to offer it as a venue for running cob building courses
We wouldn’t charge for the venue but would hope to end up with a usable structure to offer the community a place to run therapeutic activities.
In the area is access to food, parking and raw materials for cob building.
So, we look forward to replies and discussions to explore possibilities and options.
14Bikram August 27th, 2019
I am planning to build a cob house in Nepal, though in the plains where its quite hot during summer. Due to limited land size I was thinking of keeping the wall width at 18 inch. Do you think that’s okay ?
Also, we dont get commercially packed lime powder here but I think we can buy raw lime stones. How to use them in case I find them as limestones ?
Thanks in advance for your support and keep up your good work.
15Annabel Cameron-Duff August 27th, 2019
Hi Bikram, 18″ would be ok if it is one storey but if it is going to be 2 storey then you want to start with a wider base wall of 2’/ 600mm tapering (on the outside) to a narrower top wall of no less than 12″ if it is a curvilinear wall design but wider if you are doing straight walls.
It is not necessary to use lime if this is not something that is locally available. The same earth that you use for the cob can be used to make earth mortars for the stone/ brick foundation and for renders/plasters (they can be mixed with cow or horse dung to make a harder wearing exterior finish (called a litema).
Best of luck with your build.
P.S If you are interested in having some support with different stages of your build we would be happy to get involved in some way. Check out our website http://www.theroundhousecompany.co.uk to see a variety of builds we have done.