Can earth building scale up to the mainstream? 2: Kevin McCabe’s cob citadel
By rob hopkins 15th January 2014
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.
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 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!
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.
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.
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”.
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.
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: