What’s red-brick, but green all over?

At first glance, there is nothing especially odd about the three-storey (plus basement) brick house on a hill in the Chilterns, about an hour’s drive west of London. The windows and lights look typical, as does the slate roof, the five bedrooms and even the gym and home cinema in the basement. True, the field next door is full of llamas rather than sheep, but these things happen this close to London and otherwise, all seems unexceptional. But this is by no means a typical new British home.

A closer look reveals the tiles are not made of slate but recycled plastic. “That means they are half the weight of conventional slate tiles,” says lead designer, Tim Fenn, founder of the Oxfordshire sustainable building consultancy, Green Factory. Some are not even plastic but solar tiles, a smarter-looking version of the standard photovoltaic panels.

“It’s a hemp house, too,” says Fenn, striding over to inspect a block of insulation made of “hempcrete”: waste hemp mixed with lime that is much less carbon-intensive to make than other insulation materials. The windows are triple-glazed. The lights are all LED. There are two huge water tanks in the basement for storing heat that is then distributed to the house through a series of coils. “We only have underfloor heating on the ground floor, which saves installation costs,” says Fenn. Other heat comes from what he calls the “sun space”, an area with south-facing windows, and a wood-pellet boiler connected to the water storage tanks in the basement that acts as a back-up for the system.

The home cinema in the basement

The giveaway that this is an unusually green home is the muddy area down in the front of the house that is being turned into a wetlands bog, and the pond taking shape just below it. This is a natural water treatment system through which the house’s waste water will be filtered (by the bog) and stored (in the pond) before being pumped back up to the house where it can be used to wash the car or water the garden.

“You don’t need any sort of chemical treatment, it’s all done naturally by the bog,” says Fenn. “And you’ll get frogs, toads, newts and waterbirds.”

The bog in front of the house filters waste water – and will attract wildlife

The owners, a retired local couple, are at the forefront of moves to make Britain’s new homes smarter, greener and more energy-efficient. That means they are adventurous and, in this particular case, wealthy.

The house under construction

This is the first new-build eco-home Green Factory has done and it is not cheap. Tim Fenn estimates it will end up costing just under £2m. “The wealthy are the first-movers on these eco-houses,” he says, but perhaps it won’t remain that way for long. Fenn predicts rising fossil fuel prices and shortages of resources such as water means that the concept may soon become more mainstream.

Even now, he says, it is possible to make homes much more energy-efficient without adding too much to their cost. “Everyone says it’s unaffordable for the masses – bollocks. We’re building £130,000 two-bedroom houses in Bicester [Oxfordshire],” he says.

The wood-burning stove in the entrance hall

The Bicester houses are each 947 sq ft, about one-sixth the size of the Chilterns home, but have also been designed to reduce the amount of energy residents need to use, and are made from natural or recycled materials wherever possible. Like the house in the Chilterns, building materials include hempcrete, engineered timber and recycled plastic slate tiles, while solar units provide heat and electricity.

And even if there are high initial outlays for some of the low-carbon items in these homes, they can represent good value over time. Each of the nine-watt LEDs going into the house, for instance, cost £60. “But they have a lifespan of 80,000 hours, compared to 1,000 hours for halogen,” says Fenn. The solar thermal system is about twice as expensive as conventional oil or gas heating, but it will never generate fuel bills.

The woodchip boiler

And because the house is about 10 times more insulated than a conventional new home, and has been designed to trap and circulate warm air, it should require far less electricity for heating. “The owners’ power bills should be low,” says Fenn. “It depends on how they end up using the house, but they will have the choice.”

To help them understand exactly how their use of energy works, the house will have a £3,000 energy monitoring system – viewable on an iPad or iPhone – that will let its owners see which appliances or devices are consuming more power than others, and adjust their usage accordingly. “They’ll be able to see what happens when they turn the thermostat down one degree, for example,” says Fenn, explaining such a step may not make any difference to their comfort levels, but a great deal of difference to their power bill.

Chains function as a rainwater pipe

Energy-efficiency building standards around the world

There is nothing terrifically new about the idea of a low-energy house. Homeowners and office builders have been beefing up insulation, sticking solar panels on roofs and putting LED lighting in ceilings for years, all the more so in countries with rising electricity bills and limits on greenhouse gas emissions.

But these are minor modifications compared with the Everest-like effort required to meet some of the more exacting energy-efficiency building standards spreading around the world.

In Canada, there is the Super E. The Swiss have something called Minergie, but perhaps the best known is the Passivhaus, a building standard developed in Germany in the early 1990s.

Buildings meeting this standard are so carefully designed and insulated that proponents say it is possible to reduce conventional sources of warmth to the equivalent of a heated electric towel rail.

They also offer energy savings of up to 90 per cent compared with a typical central European home, or more than 75 per cent compared with an average new house¸ according to Germany’s Passivhaus Institut. And they are said to work just as well in hot climates.

There are more than 40,000 of these buildings around the world, mostly in German-speaking countries and Scandinavia, but numbers are increasing in countries such as the US and UK.

In Britain, the number of Passivhaus buildings has jumped from just one in Wales in 2008 to more than 100 in 2012, says Jon Bootland of the Passivhaus Trust, a UK organisation that promotes the standard.

That number could grow to “more than 500” in 2013, he says, assuming those now under construction are eventually certified.

Though they can be more expensive to build than conventional homes or offices, this need not be the case, says Bootland, explaining that many of the Passivhaus homes in the UK are being built for housing associations that provide low-cost accommodation.

This is hardly surprising, given their impact on energy bills. Figures vary according to individual use, but according to Bootland, the average annual energy bill for a typical two-bedroom home can be whittled down from around £800 to as little as £80 in a Passivhaus home.

Pilita Clark is the FT’s environment correspondent. Additional reporting by Peter Leggatt

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