Fashionable living: Designer Savannah Miller is turning her farmhouse into a eco-chic retreat

Fashion designer Savannah Miller has rejected the A-list lifestyle of her film-star sister, Sienna. Instead she's turning her Gloucestershire farmhouse into a eco-chic retreat.

Savannah Miller would like it to be known that she doesn't actually knit sweaters from yoghurt. Nor, she would like to add, does she exist on lentils. And finally she knows nothing about crystal healing. Having said that, she does quite like weaving, her home is full of recycled furniture and she won't use a tumble drier.

Miller, who runs her fashion label Twenty8Twelve with her actress sister Sienna, is, to put it simply, terrified by the state of the world and what we are doing to it, so she is determined to make her house as sustainable and carbon-neutral as she can. Then she intends to sell it for vast amounts of money so she and her husband, Nick, can buy a plot of land and build their own eco-house from scratch.

The plan is to buy a plot of land large enough for wind turbines, ground source heat pumps and a smallholding. They will grow as much of their own food as possible so that if things go completely wrong – and talking to her you can't help feeling that she is convinced it will – she, Nick, her stepson Java, 15, and their two younger children, Moses, five and two-year-old Lyra, can be completely self-sufficient.

That's the plan anyway. The slight hitch is that they can't afford it.

"It's mad that it costs so much to have less," she says. "It's completely upside down but you need an enormous amount of cash – it's very hard to get a self-build mortgage for example. So at the moment we aspire to living like that and hopefully we will make enough money to pull it off."

In the meantime, it is her pretty 1920s farmhouse near Stroud that will, hopefully, enable her to realise her dream. In pursuit of that dream, the Millers have raced up the property ladder. They bought their first house in 2006 for £225,000 with a mortgage of £120,000. With her eye for shabby chic and Nick's building skills, they sold it for £320,000 last year and bought the farmhouse. This too is being revamped in the same style, and on a slightly grander scale.

"We moved in last summer and it was hideous. There were swirly carpets everywhere, a sort of hideous granny annexe built from breeze blocks and plywood and no insulation at all."

The walls were quickly painted in neutral colours, with the exception of the Chinese blue sitting room and the "dirty pink" playroom.

"It's not at all designer showroom. We have used eco-friendly paints and I appreciate that they are expensive, but my husband is allergic to solvents so we had no choice in the matter," she says.

Ah yes, her husband. Nick is an eco-warrior's dream. He can build stuff, indoors and out. He can lay floors and build walls. He's also an eBay addict – great at getting something for nothing. And he's good with goats – more of which later.

When it came to the insulation, Nick managed to source a loft's worth of insulation from the auction site which, of course, he fitted himself. The couple then installed a wood-burning stove and a back boiler so there is a constant supply of hot water and warmth.

"Unfortunately in the summer it's too hot for a fire so we have to resort to the boiler, which is annoying as it's oil run, but it's the best we can do for now," she says. And when it's too wet to line dry the washing, it hangs rather stylishly over the stove.

Ripping up the hideous carpets did not reveal beautiful limestone flags (that only happens in House and Garden) – just concrete. Nick returned to eBay and, thanks to a badly written listing, managed to get hold of around £2,000 worth of reclaimed floorboards from an old chapel for £150, which, of course, he fitted himself. He also bought a whole load of old doors, which he has fashioned into a rather beautiful toy cupboard in the playroom.

"We have also applied for planning permission to knock down the annexe and replace it with an oak-framed triple-glazed kitchen that will have an Aga," says Savannah.

They have also investigated solar panels – "too expensive and not efficient enough" – and wind turbines.

"In order to generate enough power from a wind turbine we need one that can be 75m from the house and we haven't got 75m of land. So we are looking into getting a row of smaller ones on the roof that will do some of the work like power the washing machine."

And what will their Gloucestershire neighbours have to say about that one wonders? Well it turns out that a lot of people in Stroud think like they do.

"It's not all knitting yoghurt and crystal healing but we have a good group of like-minded friends and our neighbour has just asked if we want to share some goats which is fantastic."

And Nick used to run a goat farm in Costa Rica so he knows all about that too. Except that Savannah can't stand the milk.

"Everyone else loves it except me. Nick knows how to make cheese too. We won't eat the goats as Nick and the children are all vegetarian and just eat a bit of fish. I used to be but then I had my second child and I was setting up the business and breastfeeding and going up to London all the time and you can't do that on a lentil so I started to eat a bit of meat and fish now and again."

She would also like to have a vegetable garden but they haven't quite got round to that yet. "The ground is all clay here so we have had to dig that out – Nick has built a beautiful wall with it – and we are hoping to start in the spring."

Along with some more chickens – the fox ate the last lot. In the meantime they have a weekly veg box delivery.

Back inside the four bedroom house, the self sufficiency theme continues.

The furniture has been mainly provided by Savannah's "bohemian" mother.

"We haven't really bought any furniture it's all been inherited or bought from eBay, which is fine as that is just recycling too. It's lucky that that sort of style if fashionable although I have always loved a bit of patchwork.

"It's easy anyway because we can't afford a B&B Italia sofa so it's not an option.

"Although they are very beautiful... " she muses. "But it is just stuff really," she adds firmly to herself.

"We are programmed to believe that if we have lots of money and a fast car and a big house that we will be happy, but the more I have the more stressed I become. We were so happy when we had nothing. When we were doing up the last house we lived in a tent in the garden and it was great.

"I don't want to have lots of stuff. What makes me happy is being outside in the garden with my family. The Italians have got it right. They have a lovely lunch and a siesta and it's a beautiful way of life. I don't want to be working until I'm 80 to pay off a mortgage. We want to be independent and beholden to no one. I like my work but it is not the be all and end all and I am concerned about for my children as the world is in such a terrifying state."

Savannah is aware that being green is often mocked as a middle-class trend for those who can afford it, but she is passionate about the little things that people can do that can make a difference. She has recently signed up as the face of The Future Friendly 'Less Waste, More Reward' Campaign (wwwfuturefriendly.co.uk) and talks passionately about the little things that we can all do to save money as well as the planet.

"We can all turn a light switch off and that will save you money. And turn your washing machine down to 30. And don't use a tumble drier. If you visit the website you will see loads of things that we can all do and we should. We really should be doing them. And just carry a cotton bag in your handbag so you don't need a plastic one. And have a shower every day and a bath once a week. So many little things you can do."

So while she finishes doing up her house, Savannah is concentrating on the little things and is hoping that sometime in the next five years, she and her family can raise enough money to be able to afford to live without needing to spend any.