Q&A: Zero-carbon homes

What makes a home zero carbon, and what is the government doing about existing housing stock?

What is a zero-carbon home?

A home that produces zero or even negative CO2 emissions by maximising the use of energy efficiency and renewable energy. All new houses must be zero-carbon from 2016 onwards. While such houses conjure up futuristic images, the reality is they can just as easily look the same as traditional houses.

How does a zero-carbon home live up to its name?

Three words are key in the zero-carbon world: insulation, insulation and insulation. And maybe "airtightness" too.

Most of Britain's housing stock is what's called "leaky" in the sense that buildings lose heat through badly insulated walls and roofs as well as through draughty windows. In zero-carbon homes all that changes – walls are heavily insulated, floors and roofs keep heat in, and triple-glazed draught-proofed windows stop warmth flooding out.

Isn't the air stale in such an air-tight building?

No. Many have heat exchangers in the loft through which the warm, stale air from in the house is expelled while fresh air from the outside is drawn in, picking up the heat on the way to avoid wasting it. This means the building can pretty much heat itself from the body warmth of its inhabitants, cutting heating bills virtually to zero. This is all in winter, of course. If the house feels too warm in the summer, you just open the window.

What role do renewables play in a zero-carbon home?

Renewable energy technologies such as solar panels and wind turbines can mean a house generates more energy than it uses – potentially making it a "carbon negative" house. Homeowners will be paid for any green electricity they feed into the grid by the government's Clean Energy Cashback scheme, due to launch in April 2010.

What are the legal requirements for a home to qualify for the zero-carbon label?

The government hasn't decided. Gordon Brown and then-communities secretary Ruth Kelly announced in 2006 that all new homes would be "zero-carbon" by 2016, but no standard was set. The government consulted on the standard between December 2008 and March this year, and a final definition of what constitutes a zero-carbon home was expected this July – but that's now been delayed until later this year.

The finished standard will specify what percentages of a home's CO2 savings should come from energy efficiency, renewable energy generation such as solar panels on the building, and what share can come from other savings such as wind farms and community combined heat and power plants.

When will zero-carbon homes start appearing?

The first officially recognised zero-carbon home, a prototype by Kingspan Off-Site, was built in 2007. Since then, several demonstration new-builds have been considered "zero-carbon", but the first serious wave of zero-carbon homes is unlikely to appear until 2016 when housebuilders are forced by the government to meet the new standard. All homes in the new eco-towns will meet the zero-carbon standards.

How do UK plans compare internationally?

Sweden and Germany already have standards that match the UK vision of a zero-carbon house. Over 2,000 "passive house" homes – buildings that require little or no heating because they're so well-insulated – have been built in Germany, and Sweden has made the passive house standard mandatory.

What is the government doing about existing housing stock?

Zero-carbon houses are the houses of the future, but most of us will remain living in existing buildings – hence the government's drive to insulate cavity walls and lofts, install more efficient boilers and double-glazed windows. In 2010, the government will also launch a new "clean energy cashback" scheme, which will encourage consumers to fit solar panels, wind turbines or heat pumps. None of this will make most existing houses zero-carbon, but it could reduce their carbon emissions hugely.