How green is your house (and the rest of your life)?

As any 4×4 driver will tell you, the British are becoming more eco-conscious. Piloting your gas-guzzling Chelsea tractor through the streets is no longer a lofty joy, but a guilty pleasure as you try to ignore the accusing glares of other road users. Indeed, it's almost impossible for anyone to remain oblivious to climate change with extreme weather in the news daily and scientists queueing up to announce impending armageddon.

But few of us know exactly how our lifestyles affect our surroundings. The truth is, everything you do that uses energy generated from burning fossil fuels causes carbon dioxide to be released into the atmosphere. This raises temperatures, sparking off an unpredictable chain of potentially disastrous reactions. Globally, we're currently producing twice as much CO2 as nature can absorb and unless we make dramatic changes to the way we live, very soon the climate change process will develop its own momentum and become unstoppable.

It's a terrifying prospect, but help is at hand in the form of Building's carbon coach, Dave Hampton, aka Mr Sustainability.

On our website, you'll find a carbon footprint estimator that will work out the number of tonnes of CO2 you produce every year through the biggest sources of emissions - domestic energy use, driving, using public transport and flying.

Dave's purple balloon represents 1 kg of CO2 - every tonne you produce is the equivalent of 1000 of these balloons being released into the atmosphere. The bigger the balloon, the bigger your footprint is and the harder you'll have to work to reduce it.

It can be a sobering experience. Nevertheless, Building found three willing victims prepared to throw open their homes, their cars and their wine cellars to the carbon coach - and to take up the challenge of giving their lives a eco-makeover over the next 100 days. Read on to find out how they did. Our three guinea pigs will also update you on their progress with weekly blogs on the website.

Gary France: Range Rover bad, low-energy lightbulbs good

Langans Brasserie is not the most obvious venue for a carbon coaching session. With its opulent French-style decor, it looks more like Marie Antoinette's sitting room than the set of The Good Life, full of captains of industry enjoying red meat, fine wines and cigars. It's a fair bet they're not thrashing out how to save the planet.

Neither is Mace board director Gary France, on paper, a natural environmentalist. He owns three cars, does the 58-mile round trip to work in his Range Rover and flies frequently to destinations as far flung as Singapore, China, Dubai and Seattle.

Carbon coach Dave Hampton, on the other hand, showers in solar-power-heated water, burns logs in his stove and his home is lit by piped-in sunlight. He is gamely wearing a T-shirt knocked up by Building's art department bearing the legend: CO2ACH.

Dave starts with an easy question: How big does Gary think his carbon footprint is?

Gary isn't sure and, more pertinently, doesn't really know what a carbon footprint is. "I don't understand the concept of a carbon tonne. How can gas weigh a tonne?"

Dave explains that it relates to the amount of carbon dioxide produced by burning fossil fuels to generate power, and he begins to fill an A4 sheet with diagrams of the earth, chemical equations, graphs and numbers.

Gary doesn't seem entirely convinced. "It is difficult to understand," admits Dave. He tries a more down-to-earth tack: "If you think of releasing CO2 into the atmosphere like pissing in a swimming pool, the concentration in the pool has gone from 280 parts per million 100 years ago to 380 ppm today. Beyond 400 ppm, a lot scientists believe we will have floods, hurricanes, extreme weather." And he drops in his trademark analogy: "If CO2 was purple, we'd have seen the sky change colour in our lifetimes."

When it comes to the actual diagnosis, it turns out Gary is a lot more eco-conscious than it might at first appear.

Apart from the undeniable eco-sin of the Range Rover, which he says he needs to ferry his three children around, his other cars are small - a Mini and a VW Beetle. This means they do more miles to the gallon so produce less CO2, and all three are second-hand. "Recycling," Dave notes approvingly.

All but one of his flights last year were for work, which under Dave's criteria makes them Mace's problem, but Gary's holiday to see his wife's family in Seattle has added a hefty 5 tonnes of carbon onto their footprint.

This prompts a bout of soul searching. "I think it's really important for children to be exposed to other cultures, but how can you get anywhere without flying?" objects Gary. This is something with which Dave is also wrestling. His four children are clamouring to be taken somewhere more exotic than France on holiday: "They're, like, ‘Dad, can we go to New Zealand?' It's the biggest issue for me."

Dave is also pleased that Gary uses mainly low-energy lightbulbs, which he buys on the internet, and is impressively well versed in the workings of a ground water heating pump that he is considering installing to cut his fuel bills.

When it comes to ordering the food, however, Gary admits that he has never considered the carbon tonnage of his dinner. Once Dave has explained that every £10-worth of food you eat a week that's had to be flown in adds a tonne to your carbon footprint, though, he's away. All of the components of his seafood salad are local, he reckons, bar the prawns and the squid, which would have been flown in from the Mediterranean. When Gary's steak comes, he mounts a vigorous defence, despite the meat production process being highly carbon intensive. "The steak's from Scotland, the vegetables are homegrown - I reckon this is 60% local."

Even Dave can't fault it: "It does look good." One day, he muses, menus might display the amount of carbon involved in the manufacture and transport of each item.

The carbon coaching process not only focuses on an individual's lifestyle but also their perceptions of how it affects the environment, which means Dave has to tackle some difficult questions head on. Gary, for example, questions the difference that his tiny contribution to carbon neutrality can make in the face of China's growing energy use. This is something that also bothers Dave, but he does have an answer in the form of a graph showing how nations can converge their energy needs over the next 100 years. The only way to get all nations to participate is to give each an equal share of emissions. It does, however, depend on global political will - and that is a big if.

Credit: James Cant

Dave calculates the carbon tonnage of Gary’s steak and vegetable lunch – only 60% of it may be locally sourced but he admits it ‘looks good’

Graham Watts: He'd be greener than the carbon coach, if only his kids would turn off the TV.

Our second carbon coaching session takes place on a very cold January morning in north London. I encounter Dave on the way to the home of CIC chief executive Graham Watts. Dave rather sheepishly offers me a lift in his red Mini Cooper but is at pains to point out that it is a diesel and does about 50 miles to the gallon, which makes it almost as saintly in carbon terms as celebrity eco-favourite the Toyota Prius.

Dave is rather dispirited this morning. James Lovelock, the originator of the Gaia theory that hypothesises the earth is like a living organism, has just been on Radio 4's Today programme saying we might as well give up on low-energy lifestyles and reinforce our flood defences instead. This is a key debate in the eco-community but Dave is more optimistic.

It doesn't bode well for the coaching session. Graham, however, has already seen the light. He wins immediate eco-points by having all the lights turned off - the rooms' natural light is complemented by candles.

Over tea, Graham continues to impress with his commitment to low-energy lightbulbs, recycling, unplugging electronic devices rather than leaving them on standby and almost wholly organic diet, which uses fewer chemicals and so requires less energy to produce. "We try and balance the demands of lifestyle and two teenage kids with our interpretation of what's green." He adds that he doesn't drive and his wife doesn't like flying so they always holiday in Norfolk.

It is becoming apparent that the challenge will be not to convince Graham to do more, but to find things that he doesn't already do. As he leaves the room to fetch a gas bill, Dave confides that he's getting worried. "You know that feeling at the pit of your stomach. I think this guy's going to have a lower carbon footprint than me!"

He's reassured when Graham returns with his annual energy spend of £1000, about eight tonnes - the total footprint for Dave's household is only nine. "Energy use in the home is probably our Achilles heel," says Graham ruefully. "I'm constantly moaning at my youngest daughter about her PlayStation, her TV - she leaves everything on standby." Luckily, Dave's heard this before and he rummages through a holdall of eco-gadgets before extracting a meter that monitors the amount of electricity you're using at any one time and hopefully shocks you into remembering to switch off, which he presents to a delighted Graham. "My kids are the same," he reassures, "but you can't argue with a wattmeter."

Graham also promises to invest in some window sealant to tackle drafts and prevent heat loss, which should reduce his heating bills. His boiler isn't a super-low energy condensing model but since it's only six years old and he's not having problems with it, Dave can't in good conscience recommend a replacement, though he shows Graham where the internal thermostat is and suggests he turn it down a degree in summer - this can cut 10% off your gas bill.

So Dave broaches the subject of solar panels. "Would you be up for anything like that?" "It would depend on how much it would cost," replies Graham. Dave says you could get one for £1500, if you were prepared to do a bit of DIY yourself to install it. "You'd save a couple of hundred quid in the first year and, over four years, you'd get your money back," he promises. "And you'd have a talking point, and in summer, every bath or shower you had would be free!" They even go outside to have a look at the roof, but Graham doesn't seem convinced.

Graham inspects an energy-saving wind-up radio, and Dave tries to convince him that battery-free TV remote controls are the way forward

Dominic Helps: Boy's toys, new world wines and solar panels that don't work

Dominic Helps, a partner at solicitor Shadbolt & Co and Building columnist, declares himself "a bit of an ignoramus, a CO2 virgin" when it comes to living a low-energy lifestyle. "I've taken no steps whatsoever to become eco-friendly," he laughs. Nevertheless, I catch him turning the thermostat right down before Dave arrives.

The carbon coaching process involves not only changing people's lifestyles but challenging their perceptions of the dangers facing the planet. Given Dominic's legal background, Dave is expecting this to be his toughest call yet. Why, he wonders, did Dominic agree to take part? "I suppose I was interested. I'm aware of environmental things generally but more in macro terms rather than in terms of one's own house."

So on a scale of one to 10, how much does Dominic believe in manmade climate change? He thinks about an eight. Dave says he's a 10, but that there are still a few people who believe it's all a myth. "You can't exclude nature altogether," argues Dominic. "I'm a lawyer - eight is the equivalent of a 10 for me. We're usually five or six on everything."

So, one to 10 again, how important does Dominic think it is? "I think it's probably the most important thing," he says. "Poverty and inequality are a consequence of environmental factors."

Dominic has a cause of his own: he wants to save the tiger. In December, he fulfilled a lifetime ambition to visit India and see the animals in the wild, and now he's planning a campaign to stop the government-tolerated decimation of their population by poachers. Despite the harm done by the 10-hour flight to Rajastan, his commitment clearly forges a bond with the carbon coach.

"Put it there!" exclaims an overjoyed Dave, shaking him by the hand. "You're a fully fledged environmentalist, aren't you?"

Dominic has lived in his cosy Reigate bolthole for 10 years. Until he married last year, he considered it his "bachelor pad" - not difficult to imagine from the Arsenal memorabilia pinned up everywhere.

Dominic suspects his carbon footprint has recently expanded with the replacement of his creaking, inefficient central heating system. First port of call is the cupboard under the stairs. Dominic flings the door open: "We had to strip out the entire system - it was like Heath Robinson in here," he says with obvious relish. Above the boiler cupboard in the kitchen, a relic of the chaos remains in the shape of the control panel, a baffling array of dials, coloured buttons and lights. "This is a unique piece of equipment," says Dominic proudly. "Nobody has ever seen anything like it - you can press all the buttons, it makes no difference to anything."

But the best is yet to come. We venture outside and stand shivering on the lawn, and Dominic gestures expansively upwards. "You've got solar panels!" says Dave.

They were installed when Dominic bought the house, they don't work and he's been having the devil of a time trying to find someone to sort them out. "I looked through the Yellow Pages. I must have phoned 15 or 20 companies locally and not one of them wanted to know. I ended up talking to someone in Wales." The confusion didn't stop there. "I thought, there must be something in the loft space, so I sent my gardener up to have a look around but he reported that it had been partitioned off." Dave suggests that the control panel in the kitchen might be something to do with it. "Brilliant!" exclaims Dominic. "The man's a genius! Can I have him full-time, living in the shed?"

We return to the warmth of the house. Back in the kitchen next to Dominic's impressive wine collection (unfortunately much of it flown in from the new world), Dave explains his trademark purple balloon. "This is 1 kg of carbon dioxide, the amount you produce if you leave the television on for 24 hours, drive four miles in your car or have the boiler on for 15 minutes."

"Are you serious?" asks a shaken Dominic. "Picture 10 binbags filled with soot," says Dave, "that's how much CO2 you produce for every binbag or wheelie bin of rubbish you throw away." "Oh my god!" says Dominic. "But how does leaving the TV on convert into CO2?" Dave explains that it relates to the amount of fuel you need to burn to produce the electricity. "What if I leave it on standby?" asks Dominic.

It's a pertinent question, given the number of devices that he has in his front room. There are no fewer than seven remote controls on top of his giant flatscreen television and a spaghetti junction of plugs concealed behind. "Plugs are not one of my strong points," he admits. "This is pretty good compared to what it was - I had to get an electrician out to sort out the wiring."

Dominic is a complete naif in the field of low-energy lightbulbs too: "Do you mean using a 40 W instead of a 100 W?" Dave extracts 20 W and 13 W versions from his trusty holdall and explains that they last five years and can save almost half a tonne of carbon over their lifetime. "Good god!" says Dominic. "I've never seen these in Morrisons or Tescos." "You're a pioneer now, you have to go on the internet. If you change the whole house in one go, you'll get a real shock," promises Dave.