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Transition Culture - an evolving exploration into the head, heart and hands of energy descent

Can earth building scale up to the mainstream? 2: Kevin McCabe's cob citadel

As part of our month's exploration of the theme of 'scaling up', I recently visited Ottery St. Mary in East Devon to see Kevin McCabe, his wife Rose, and the extraordinary new cob house he has spent the last 3 years building.  In the recent edition of Grand Designs in which the house featured (see below), presenter Kevin McCloud referred to Kevin as the "King of Cob".  "He doesn't want to build a cob house", he continued, he wants to build a cob citadel", or as his son Ben put it, a "Utopia of cob awesome-ness".  Kevin, McCloud continued, is "determined to prove that cob has a future as a 21st century material".  But does it?  Can cob scale up from its present niche status to become a mainstream approach, and what can this building teach us about that process? 

The Cob Citadel

The Cob Cottage Company in Oregon's newsletter, 'CobWeb', describes itself as "a newsletter for people with cob stuck to their souls". I am one of those.  So visiting the McCabes' home, which looks like a cob housing complex, is akin to getting the keys to the sweetshop.  There's the family home, an incrediblely gorgeous cob house, as well another smaller cob "teenager cottage", a cob workshop, cob outbuildings, a recently-built cob farmyard with storage and more workshops, and now, under construction, the largest cob building ever built (probably).  It's that new building that was the subject of our visit.

Looking across the various buildings to the new 'citadel', far right.

The scale of the new building is breathtaking.  It's huge.  The scale was, in part, determined by the route to planning.  With further building unlikely on their plot, they applied to be the first people in Devon to take advantage of the Planning Policy Statement 7 which permits "houses of exceptional merit and contemporary architecture to be built in areas not normally designated for development".  It sets out a number of detailed requirements for buildings in rural areas including use of environmentally friendly resources, materials, overall sustainability and enhancement of the local environment.

The new building taking shape.

The walls are built from 1500 tonnes of cob, all mixed onsite, with subsoil from the site.  Traditionally, cob buildings are meant to only be built during the cob building 'season', traditionally from "when the swallows arrive to when the swallows leave again".  These walls were built during the wettest summer on record, and were still being built, four-storeys high, in December.  One section of wall, at the highest point, 33 feet from the ground, shows deep finger holes in the wall about 8 feet below the top. When I asked why the holes were there, he said that while the last cob was being put on the top of the wall, 15 feet below, the cob was still wet enough to poke.  Kevin likes to push this material to its limit!

The tallest section of wall, 33 feet from bottom to top.

Cob as "a 21st century material"?

Kevin and I sat down for a chat (the podcast of our whole conversation is at the end of this post), and I asked him whether he thought, having built this building that pushed cob so far, he felt it had potential to go mainstream:  

"I think it would be difficult to be a mainstream building material. And I’m not that interested in it becoming a mainstream material, which might disappoint you! It could certainly be a lot more mainstream than it is but it’s always going to have some disadvantages. You need a relatively big site because if you try to use the material off the site, which you always can to a greater or lesser extent, that still means digging a hole somewhere to mix the cob in. To do it efficiently you need to get machinery around the building, as you do with any building I guess.

But for large-scale housing developers there are disadvantages of cob: the volume of material, thickness of walls, that sort of thing, which probably don’t make it ideal in a lot of situations. But where you’ve got a bit more space, the kind of development which I would like to see more of, then it is eminently suitable".  

One of the aspects of this new building that has divided opinion the most has been Kevin's decision to try and push cob to PassivHaus Gold levels of energy efficiency by adding a skin of external insulation to the outside of the building.  On its own, a cob wall, Kevin is confident, could reach Code 6 in the Code for Sustainable Homes, the standard which all new builds will need to meet by 2016. As Kevin told me: 

"I don’t think you need to insulate cob walls. This house (the farmhouse where we did the interview) has got 3 foot thick cob walls and it’s very well performing. Just to put some figures on it, we’ve got 5,000 square feet heated from one 12 kw heat pump which costs about £1000 a year to run in electricity, a ground-source heat pump. If you compare that with any new building, I think you’ll find it’s pretty favourable.

What we did with the new building takes it to the most ridiculous level of any building, i.e. Passivhaus. I thought well, if I'm going to do it I might as well just really go for it and take it to the most extreme level. I wouldn’t necessarily expect that to be repeated. I’m just really showing that it’s possible".

It is perhaps Kevin's choice of insulation that is proving most controversial.  Polystyrene sheets.  

Polystyrene cladding being fixed into place.

Why wrap a breathing, as locally-sourced as possible, building material in petrochemicals?  It's a tension Kevin acknowledges:

"The choice of polystyrene is a bit controversial for anyone who’s into natural building. It’s obviously not a natural product, but the natural alternatives had their challenges too:

  • Straw bale might actually be quite a sensible way of insulating on the outside of cob,  but I don’t think it’ll last anywhere near as long. People are always quoting particular kinds of buildings in the States which have been there 120 years or something, but I’m pretty confident that you won’t find any straw bale building in this country still in good health in 120 years’ time. 
  • Rockwool, which would be quite sensible, but would end up costing almost twice as much to get the same level of insulation in a renderable form
  • Wood fibre would be about 4 times as expensive
  • Lime hemp about 7 times as expensive.

That’s how I came to polystyrene. On a project that’s so big, those costs are obviously very significant. We’re on a relatively tight budget for such a large project".

The kind of polystyrene Kevin is using was chosen for its high insulation value, the relatively low pollution value of its manufacture, and its having an A+ rating as a building material.  It's completely recyclable and non-toxic.  The other issue this raises is about the breathability of the walls. He will wait until the walls have dried before cladding them, but is confident that the walls will still be able to breathe enough.  

The existing family home, built from cob about 15 years ago.  Gorgeous.   

Removing obstacles to mainstreaming cob

Kevin is clear that the scaling up of cob building, it becoming more of a feature of new developments, won't happen by accident, as developers tend to do what they know:   

"Council planning departments can’t insist because developers will appeal against it. You can’t insist on one thing in one part of the country if a developer can show in another part of the country this wasn’t insisted upon. And that’s where the planning laws perhaps need to be altered so that you can.

If you put developers in a position where they have to do things, they actually miraculously find ways of doing them. Unfortunately, the way things are structured, if they can show a precedent somewhere else for not having to jump through these hoops then they will. I don’t think there’s a reason why you couldn’t do a large part of that development in cob, but the reasons are all in the planning. A developer who probably is only interested in the bottom line, will make money more easily, more safely, doing a more conventional build".

Kevin brought up Cranbrook, a new town of 2,900 homes being built near Exeter:  

"I know for a fact that East Devon District Council were keen to push for cob or at least some cob building at Cranbrook. But they can’t insist – the planners actually have a lot less power than people sometimes think they have. All the local feeling would have been in favour of some cob there at Cranbrook. It probably would have cost slightly more in the short term, but not much". 

At the moment, both Code for Sustainable Homes and PassivHaus certification fails to take any account of the distance travelled by building materials.  If the government were serious about building new houses, and encouraging innovation and enterprise at the local level, specifying a percentage of local building materials could be a key innovation.  Writing it into legislation would get around situations, like Cranbrook, where people want it, Councils want it, but developers brush it to one side.  If the government is able to, within a short period of time, change tax regimes, subsidy structures, planning legislation and so on in order to roll out fracking on a large scale, surely the scaling up of cob, or other green building measures would be a breeze?  

Another challenge to scaling up cob is the skills gap.  When Kevin started cob building there was only "one old guy in Devon who knew a bit about it.  Aside from a one-day course, Kevin is self-taught.  But how to fill the skills gap?   

"Yes, there is a skills gap, but I think that could soon get filled.  It actually isn’t that difficult to learn. There are quite a few design considerations which are important to understand but I think that learning curve would be quite easily handled. I think the problems are much more in people’s perception than the reality". 

Load bearing cob columns (something I've never seen before!)

Why scaling up cob is about much more than just cob

Can cob building scale up?  This month we have been looking at how Transition might scale up, and there are comparisons with the challenges cob building faces.  What I love about what Kevin's doing is that he is pushing a traditional material and seeing how far it can go.  There are a number of earth building techniques (rammed earth, adobe, clay plasters, clay/straw etc).  What, I wondered, is so special for Kevin about cob?

"I’m probably quite prejudiced. To me, part of the joy of cob, apart from the fact that it is the vernacular material here in this part of the world, is its sculptural nature, which no other earth building technique has to the same degree. It’s also very strong compressively, as I’ve demonstrated with these pillars (see above) – each pillar is holding up several tons. So to me, I would certainly want to put my energies into promoting cob rather than other forms of earth building, particularly as I live in this part of the world. It’s got so much further it could go yet. Yes there are a lot of other things, and people who are expert in them might well have other arguments for how they might be scaled up. I don’t know. For me, cob’s the way forward". 

Some may argue that Kevin's house is too big to possibly serve as a model for anything, especially those for whom the most exciting, empowering aspect of cob is how it makes small, mortgage-free, locally sourced, collaboratively-built homes a possibility for people.  Some may argue that wrapping cob in polystyrene undermines the mainstreaming of cob, as it represents a public acknowledgement that it can never attain the insulation levels required (as one green building expert suggested to me "I wonder if he didn’t just set cob building back 100 years in a desperate attempt to prove a point").  

But for me what matters is that it is happening.  While you may not like the polystyrene cladding (it's not something I'd do, but then I wouldn't ever build that big nor feel confident enough to) it introduces cob to a new audience, gets people talking about it, changes the story, challenges orthodoxies and rigid thinking about possibilities.  

Where two buildings meet.

Scaling up cob though, like Transition, is not about one-size-fits-all.  Traditionally, each part of England had its own vernacular building traditions, determined by the materials available locally.  In Devon it was cob, in Shropshire oak timber frame, in Yorkshire stone and slate, and so on.  It's not about building cob everywhere, but about reconnecting to those vernacular materials and techniques as being key to local economic regeneration, rather than reshaping the nation in cob.  As a 2010 report by the Prince's Trust for the Built Environment showed, there are very real benefits to local economies of doing so.  

Scaling up also needs pioneers prepared to put their heads above the parapet and to take risks.  It requires people who push and educate the authorities, building inspectors and so on, introducing them to new thinking and inspiring them with new ideas.  It requires stories, things that get people talking about "did you see?" and "I heard about this amazing project the other day", and as Transition shows, you never know where those stories can go.  It also needs people who contribute to building an evidence base, as Kevin his, using moisture sensors and other ways of monitoring how the building behaves.  

As Kevin told me: 

I’ve got an experimental mind. I’m still experimenting 20 years later. I’m quite brave, I don’t mind taking risks, because you don’t really push the boundaries unless you take risks. I’ve always found that worthwhile.

I headed home with a bit more cob stuck to my soul than previously, awed by what Kevin has achieved thus far in spite of the wettest summer on record, ongoing extreme weather and financial worries.  The future needs pioneers who are always aiming higher and looking to the next thing.  The really awesome thought is one he's finished this one, and got twitchy again for another project, where he'll take it all then...

In case you want to hear our conversation in full, here's the podcast:

Arts & Crafts


Robert Alcock's picture

Cob is inherently anti-mainstream

Hi Rob

Well, I could hardly refrain from commenting on this!

I think most cob self-builders would agree, the really great thing about cob is that it is an inherently anti-mainstream material. By that I mean that it lends itself to working in ways that are inimical to the specialized, professional, capital-intensive, alienating conventional building industry.

Unfortunately, what Kevin McCabe has done here, in order to get around the absurd English planning regulations, is to take cob into a territory where it is about as far from its roots as the self-builder's material _par excellence_ as can possibly be imagined.

It doesn't surprise me that he decided to wrap his building in polystyrene. Once you have decided that the way forward is towards monumental scale, you're already firmly in the territory of the alienated building industry. Don't know about the costs he lists, but wood shavings are free (a waste product of sawmills) as an additive if you want to improve the insulation value of your cob. We did this in the main wall of our house. (We did use polystyrene in the foundations, however -- we're not purists.)

Yes, cob is labour-intensive the way it's normally done. But what kind of labour? Throwing balls of mud and kneading them into a wall with your bare hands? Getting in close contact with earth, the mother material? Most people would consider that play, not work. More than 200 people (volunteers) worked on our house and i think most of them had a great time doing it. There's no need for huge machinery. We used mainly a rotavator and a wheelbarrow. It doesn't just build a house, it builds health and community. Unlike the conventional building industry which is one of the most unhealthy to work in.

I could go on... In fact I'm currently trying to write about the experience of self-build with cob. The trouble is, doing it is so much more fun than writing about it, it makes it kind of difficult to stick your bum to the chair...



Philip.Barnes's picture

One concern

So I have a concern about "scaling up" cob in this instance because it seems to me, on an admittedly very superficial level, that what Kevin has done is scale up the size of his house.  If the objective of this envelope-pushing experiment is to demonstrate the feasability of utilizing cob for the construction of gargantuan single-home housing structures, then I'd consider this a rousing success.  But this is incompatible with the ecological and social philosophy of using this appropriate technology to live simply.  Real questions need to be asked about what we want cob technology to enable - and how we want it to "scale up".  Do we want it to enable widespread construction of huge single-use homes like Kevin's, or do we want it to enable the widespread construction of structures of similar size but of alternative use - theaters, community centers, and other civic spaces?

I also think we should take away a lesson from this story.  Kevin got himself in trouble by trying to do too much, by pushing the limits of what was possible.  He ran out of money and his "citadel", militaristic metaphor aside, is still incomplete.  The lesson that I take away is that when you need to be very cautious not to lose resilience when you apply a small-is-beautiful appropriate technology in a somewhat antithetical context because you will likely find yourself up against limits - in this case financial limits.

Rob Hopkins's picture

You're one step ahead of us there!

Hi Philip... good points... Robert, whose comment is above yours, is going to do a piece for next week that will address some of the very points you are making here.  I think there is still a place for the the odd one off thing that just pushes things to an extent that takes the breath away....

Thanks for commenting. 


Marian van-der-Veen's picture

Cabe's Cob in St. Ottery and the nature of building with cob

Thx for this post and valuable comments! I smilingly feel the same drive to work with the stuff, rather then writing about it! After reading the comments here, I guess the choice is in living conditions that are characteristic for building with cob, when no alternative was present at that time..... or merging it with present day materials and scaling up in size or ambition. Before leaving Holland, spring 2012, to live and work as a volunteer in communities, I consulted a holiday-tips-and tricks booklet, found a note on the use of cob houses in the UK, mentioning "There's one left in the countryside, in Mary St. Ottery" it said. I visualized a Zoo with otters, to be honest, with animal cob housing, otters playing with cob maybe...  ?? (my imagination is very vivid)

In april 2012, during my stay at Monkton Wyld Court Dorset, on a day off, I went by bus for a visit, expecting to find "the one cob home that was left" as a museum/curiosity.   After consulting several villagers, I was instructed to walk out of the village and to my surprise, I found the cobbuilding-project of Kevin McCabe. He allowed me to make pictures from the street, but I wasn't allowed to make any on the building site, which I understood completely. I had the impression, that his wife was weary of curious eyes, who knows.... much more happy with working the cob? Kevin told me, there are many cob houses in Devon, over 200 years old. Also he accepts volunteers to work with him, when I asked him about it.

From then on, I found many cob houses, sometimes derelict with the material showing clearly. When lived in, they're the ones with off white, brownish, pinkish painted, somewhat irregular wall surface and a black painted part at the bottom, all along the   outside of the house. All natural material is ever lasting, if you know what I mean, but that doesn't count for its form-creations and maintenance of its form is inherent, while living with it. It's a matter of lifestyle, if that aspect is being welcomed or not, I guess. The fine conditions of these ancient cob homes proves the value of cob, as a buiding material, to me.  

Climate change is a condition to be reckoned with though, considering the increase of rainfall in Britain! Changing from "historing" to "restoring" old ways of living, I guess that's part of the planning/decision making: acceptance of the change in living conditions, on the long run.

Robert Alcock's picture


After watching the Grand Designs programme, some of the reasons for Kevin McCabe's design choices became clearer to me...though not the original decision to build at this massive scale.

Given that he's decided to build on a pharaonic scale, the decision to go for Passivhaus standard by wrapping the building in polystyrene is partially clarified... The huge scale of the building makes any kind of heating system a non-starter in both capital and running costs.

Still, I wonder if avoiding a heating system couldn't have been achieved using a combination of:

(1) south facing glazing (has this been incorporated into the design at all? the programme doesn't make it clear)

(2) earth sheltering (not easy with a 3-storey building, true)

(3) unheated buffer spaces (barn, storage, etc.) to the north of the building, and

(4) natural insulation -- including but not limited to the types he mentions.

But I'm still scratching my head about how anyone could be mad enough to WANT a house this big...

Philip.Barnes's picture

Design principles as a function of scale

Robert, Rob,

I also do not have a problem with Kevin using polystyrene insulation simply because he is trying to demonstrate the possibility of using cob to achieve Passivhaus standards.  But again, we need to ask the question why there is even a need for a Passivhaus demonstration project at this physical scale, which, to me, is counterintuitive.

Robert, I'd like to follow off of what you just wrote to try and make a broader point: The design principles that were used to build this house are a result of the physical scale of the project.  Kevin cannot utilize earth sheltering because the house is so big.  Likewise, the effectiveness of unheated buffer space on the north side would be limited unless it is the same height and width of the structure.  It seems to me that Kevin's decision to super-size compelled him to focus on ways to capture efficiencies (heat exchanger, polystyrene insulation, etc.).  Now, there is nothing inherently wrong with efficiency, but we might want to consider whether prioritizing efficiency as a design principle comes at the expense of sufficiency - a design principle that is more closely aligned with small physical scale.  In this instance, I believe Kevin traded sufficiency for efficiency.  And this circles back to my earlier comment about the relationship between scale, limits, and resilience.  When efficiency is prioritized as a design principle because a project is scaled up, limits are pushed and resilience is lost.  On the other hand, when sufficiency is prioritized because a designer self-imposes a modest scale, limits are respected and resilience is gained (or maintained).  The point I'm making is certainly up for debate but if this is true, which I believe it is, then it shifts the way we approach and evaluate our development decisions.

Anyway, great discussion and I thank you for stimulating it!



Robert Alcock's picture

push that envelope

Yes, agreed on all points. But I think the person we really need to thank for stimulating this discussion is Kevin McCabe for his bonkers house. There's pushing the envelope and then there's pushing the envelope -- maybe it's in the wrong direction, but he bloody well pushed it.

Anyway, I'll try and expand on some of the ideas in these comments in my upcoming post...

Philip.Barnes's picture

I stand corrected


You are correct, I should acknowledge that Kevin initiated this discussion by deciding to build his utopia of cob awesomeness.  It would be interesting to hear from the man himself about the points we've raised here.  I wonder what he thinks of our discussion.  In any case, I look forward to reading your post.

Somewhat related to this thread, one of my favorite homes featured on Grand Designs incorporated reusable materials (tires, wine bottles) and earth sheltering/passive solar heating techniques.  If you've got an hour to kill, you can watch here:



Thanks for your comments.  Yes, sufficiency is absolutely a subjective term and as you point out is as malleable as cob.  I love the comparison!  Addressing the flip side of your thought about how "sufficiency is embodied and applied", I think it is quite clear that despite the subjectivity of the word, very few people could seriously argue that Kevin's house "embodies and applies" sufficiency as a design principle.



Marian van-der-Veen's picture

Sufficiency, a subject as mallable as cob?

Hello discussion group! To me, searching (in books and internet, not by traveling) for architecture in all sorts of cultures and of mostly natural material, living with the question "How to live together?" this is an interesting discussion. I'm looking at it in a feminine way, amongst the men here, if I'm right ;)

The comment of Robert Alcock, made me wonder how subjective "sufficiency" is embodied and applied, nowadays. Here's the meaning of that word:

Often the size of a building, like an office or church, is associated with the organisation's/architect's/deity's ego and the need for making an impression (as I've noticed from remarks by people looking at such an object). I don't mean to imply  that this is the case with Kevin Cabe's plan and building structures, it might be that he's simply trying to find out what works for him and what not, while working with cob.           And other materials. Maybe he envisions a village on his land, an impressive estate in his own style, for whatever reasons, who knows? He certainly sticks his neck out, above the haycutting level, or how you call it in England..... Which, to me, is a very brave thing to do.

And sometimes people start big projects, in fear for the moment of completion.         Once it's finished...... then what? Believe me, I have no reason to imply this in Kevin Cabe's case, it's just an observation of how people choose their projects in general.       At least once I've noticed this clearly in a person, building his own strawbale home, postponing the completion by finding all kinds of non-sensible-reasons, in order to NOT finish it. I'm still sending supportive energy for him and his family, so that one day they enter the house and make it their HOME!    

And now, I feel my post needs something substantial. I give you the titles of 2 books Shelter I (1973) and II (1978) by Shelter

Part I  ISBN 978-0-936070-11-7  $ 26,95

Part II ISBN 978-0-936070-49-0  $ 19,95

Great books to marvel at architecture from all over the world, excellent pictures, drawings (also of technical details) and good stories from builders and travelers/explorers.

Shelter I was a book I found in a collection of papers and magazines, the "never-ever-getting-there-person" offered to his volunteers, for reading. I've enjoyed it thoroughly at that time (summer 2012) and ordered the 2 parts last December 2013 at the American Bookshop in Holland. If you decide to order them, I really hope you will enjoy them too!



KesterRatcliff's picture

what's actually the problem with polystyrene? 

When they eventually run out of polystyrene from petroleum to recycle, by then the biotech replacements using algae and sunlight to make hydrocarbons which can be processed into polystyrene will probably be ready. 

If BRE is even nearly right, the amount of energy saved is well worth it. 

Even photovoltaic solar panels currently require indium and gallium, which are too rare to scale up to replace enough electricity from fossil fuels. (I'm aware there are new semiconductors using much commoner metals in development, so it'll probably be fine, but it's a similar kind of problem to polystyrene, i.e. not a very bad problem.) 

Also that polystyrene's going to stay there for centuries. Worth it.