No we're not talking about corn cob homes...not yet anyway.
are another variation of earth homes. Cob and adobe are identical in composition, the difference being in the way the material is used.
Like adobe, cob has a very long history, probably one of the oldest of any building material on Earth. In fact it predates history by a long shot, probably going all the way back to the Paleolithic Era. In more recent though hardly contemporary times, it has been widely used throughout recorded history in Britain and Ireland.
In it's present incarnation it is presently enjoying a renaissance, particularly in
Canada and the US, a number of countries in Europe and Australia and New Zealand. The main reasons, I suspect are the almost universal availability of the materials, mostly earth, clay and straw and the fact that almost anyone with a little practise can learn to be a cobber. This is a definite plus if you're assembling large work parties from a pool of friends and family, which is the way your typical cob house seems to get built.
Cob construction is definitely labour intensive and a real workout. The somewhat quaint and outdated concept of work bees is the best way to build a cob house and for that reason cobbing has a bit of a fringe reputation, I think. When's the last time you successfully organized a large volunteer work party to engage in dirty heavy manual labour in your neighbourhood? Not to say it can't be done but it would be a good idea not to be stingy with the cold beer.
Building cob homes does involve an awful lot of mixing, carrying and hand packing the stuff on top of your walls. There are mechanized means of aleviating these tasks to some extent and I would highly recommend most of them. On the other hand if you enjoy dirty dancing, then cobbing might just be for you. From most accounts, the most popular way to mix cob is dancing barefoot in a big vat of the goo with a partner. Some of you boys might be rolling your eyes at this point but you never know... maybe you should try it.
Anyway, indiosyncracies aside, a well-built cob home is strong as the proverbial brick outhouse and provided it is either finished with a weather resistant plaster or protected with ample eaves, these places can last a very long time. There's plenty of cob homes in Britain that are hundreds of years old and still going strong.
Cob construction lends itself well to the organic "hobbit house" look with lots of free form curves and sculptural features. This in part evolves from the need to make cob walls thicker at the bottom than the top. And also in part I suspect from all the beer or other inducements you need to ply your volunteer help with. My own opinion is that the creative impulse should be tempered by at least some consideration of a possible resale down the road. Kind of like that tattoo of a long gone girlfriend you wish you'd never got.
Insulating cob homes in colder climates can be problematic. Despite the straw content dried cob has a very low R-value as you'd expect. Since most folks would probably want an earth or lime plaster on the interior walls rather than the spray-in-place foam look, the only option is to build some form of insulation into your walls. This could be done by adding higher R-value material like vermiculite to the mix or perhaps by integrating rigid foam board into the walls. I have heard it suggested that straw bales be used on the exterior. But if you're going to do that why not just go straw bale in the first place? A combination might be the answer with cob on south-facing walls that can absorb daytime solar energy and radiate it back into the house on cold nights.
Cob does have high thermal mass and because of the thick walls would in theory work best in climates with relatively high daytime temperatures and cool nights, just like adobe. Ideally we like to see the heat migrate slowly throught the walls during the heat of the day in time to radiate warmth at night and then the whole process repeats in a cycle.
Why exactly cob construction has caught on more in cooler climes where it's not as energy-efficient is a bit of a mystery. I guess maybe in Britain they have a long and time-honoured tradition of freezing in their cob homes but it's a tradition I for one wouldn't want to emulate. Happily, more insulative material such as sawdust or vermiculite can be added to the mix to increase the R-value of the walls.
Undoubtedly, resourceful cobbers have and will continue to overcome these problems. However, cobbing is clearly not for everyone and you'd be well advised to do your homework carefully before taking the plunge.
Now that I've finished being a stick-in-the-mud (mud-in-the-stick?) I've just got to add that the cobbers I've encountered have to be some of the nicest people around and sure do enjoy themselves. And the craftsmanship on some of these places is second to none.(see also "Cob Gallery" on this site)
So if you've got lots of fun-loving friends and neighbours who don't mind getting dirty helping each other out then a cob house might be just the way to build. Under the right circumstances, a beautiful and cosy cob house can be built on the proverbial shoestring and chances are you'll have a good time doing it.
Finally, it is interesting to note that in Australia, the word "cobber" is used synonymously with buddy, pal or mate as in "G'day, cobber." It is believed that the derivation of this usage comes from the early goldfields when the leftover clay-soil from the gold pits was used to make huts for the miners.
Images courtesy of Patrick Hennesy of
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