Mud, glorious mud

Using mud as a house building material had its origins in cheaper homes for the poor, says Graham Norwood. But its environmentally friendly credentials means it's first choice for wealthy housebuilders with a conscience

These days there are wooden homes, pre-fabricated steel homes and, of course, plenty of brick ones. But why, you may ask, are we still building mud ones? The answer is that mud, or Cob as it is known to architects and specialist builders, is the new black for growing numbers of environmentally-conscious buyers. "The clients tend to be very committed to historical and environmentally-sound methods of building so they want the whole package," according to builder Chris Brookman of Back To Earth, a specialist cob construction company based in Devon.

These days there are wooden homes, pre-fabricated steel homes and, of course, plenty of brick ones. But why, you may ask, are we still building mud ones? The answer is that mud, or Cob as it is known to architects and specialist builders, is the new black for growing numbers of environmentally-conscious buyers. "The clients tend to be very committed to historical and environmentally-sound methods of building so they want the whole package," according to builder Chris Brookman of Back To Earth, a specialist cob construction company based in Devon.

The 'package' can often consist of thatched roofing, original material like lime putty and limestone renders, recycled water systems and traditional wooden windows - but it is the Cob that marks out a property as truly distinctive.

Cob walls consist of hardened mud and straw, usually mounted on a stone plinth to try to stave off rising damp. Cob came into widespread use in the 14th century and its buildings are most common in south west England - where the clay is strong and does not expand or contract too vigorously - although some cob homes are also found in Wales and along the south coast and north east of England, where heather and animal manure was added to the mix.

"I started building with cob at the end of my university degree. It was only going to be for a few months but I enjoyed it and thought I'd see if I could make a living. It beats being in an office," says Brookman, whose firm is seven years old and builds cob properties from scratch - including some at The Eden Project - as well as repairing period homes made from the substance.

One of the material's drawbacks is dampness. Most of those still standing (and all new-build ones) are coated with flexible lime plaster; cement render was used on some but because this is inflexible it tends to crack, allowing dampness to penetrate.

Unsurprisingly, because of this potential for dampness, surveyors and house insurers are not fans of the material.

"It's been a problem in the past. People want an old property and get a survey on somewhere we find for them but they then worry when they're told it's got cob walls - especially when they're told precisely what cob is" admits Nicola Oddy of the Cornish branch of Stacks, a property finder service.

"Some buyers used to back out but there have been so many examples of successful cob properties just being built that the material is getting a more positive image," she says.

An additional disincentive is the high insurance premium required to cover rebuilding. If a cob property is listed - and many are - its walls will have to be rebuilt from the same material, which costs two to three times as much as modern bricks.

But one owner who swears by the stuff is public relations consultant Nicky Checkley, who for 12 years has lived in an 18th century cob cottage in the Cornish village of Lezant. "You can't beat it. It's cool in the summer and warm in the winter. We need very little heating even during the coldest days" she claims.

"The windows are a little ill-fitting - that's pretty typical of cob buildings - but there's never been a major problem. It is as economical and as comfortable and efficient as the modern bungalow which our neighbours have next door," according to Checkley, whose home also includes a listed cob barn.

The return to the rural skill of cob building has been championed by Plymouth University which now run courses on using, repairing and conserving the material.

"We also ran awareness courses for home owners. We'd go to village halls and tell owners who didn't really know much about the construction of their homes exactly what was in cob and how important lime putty was," recalls Sue Harding who now helps run the Cob Construction Company but used to be assistant co-ordinator at Plymouth University's splendidly named Centre of Earthen Architecture.

Harding says such courses are largely unnecessary these days because current and would-be owners are better informed about cob. This is because of the emergence of advice websites like www.periodproperty.co.uk and even up-market TV makeover programmes such as the BBC's Restoration series, on which Harding has appeared.

"Modern owners are very willing to source materials. Also people with the skills and know-how are also much more available today, although they come at a cost" she says.

Ironically, cob - which originated as a cheap way of creating homes for the poor who could not afford early bricks - is now a building material of choice for the wealthy with a conscience. Estate agents say the presence of the material can add a premium to attractive period properties, such as cottages or former workers' longhouses.

"It's not a cheap material because it's very labour intensive to construct so people who have it know they possess something special. But it's sustainable, economical to run once constructed and perfect for the environmentally conscious" says Harding. "Ironically, it's become the ideal 21st century building material".

Back To Earth (01363 866999); Cob Construction Company (01392 834969); Stacks ( www.stacks.co.uk)

COB PROBLEMS

'Wall spread' as old ties around the cob walls break or decay, allowing the material to spread

Rising damp caused by soil building up around the stone plinth over centuries of use

Decaying old thatch allowing rain to penetrate at the top of cob walls