With street names such as Temperance and Hygiene and plenty of green open spaces, the 1920s Bon Air (Good Air) housing estate in a working-class district of Brussels was meant to provide a healthy "garden city" way of life.

Now 21st-century planners are striving to turn it into a modern ideal with the kind of renovations EU policymakers sitting in their shiny offices across the city want to see throughout the European Union.

Work starts in Bon Air in September to transform a prototype from damp and dingy into a light, well-ventilated and very low-energy home.

It is the model for 86 social houses in Bon Air and La Roue (the Wheel), another housing estate in the same Brussels district of Anderlecht, with a budget of 17.4 million euros ($19.7 million).

In the European Commission, meanwhile, policymakers have begun a review of EU buildings law.

The aim is to work out how to enforce requirements that all new buildings be nearly zero-energy by the end of 2020 and to transform existing property, including through deep renovation, meaning tackling 80 percent or more of a building and cutting energy use by a similar amount.

As a bloc, the 28-member EU spends more than a billion euros a day on importing fossil fuel, much of which is used by buildings, chiefly for heating and cooling.

The Commission says buildings consume 40 percent of EU energy and the potential for savings is vast as three quarters of property is inefficient.

Smarter building, it says, creates millions of jobs, fuels growth and cuts health bills: insulation cures the damp that causes asthma, while using less energy lowers emissions and improves air quality.

The industry says it is Europe's answer to the U.S. shale gas revolution, which has greatly reduced U.S. energy costs.

"This sector is ready and waiting to eclipse shale gas as the biggest source of energy saved in this case," Barry Lynham, director of strategy for German firm Knauf Insulation, said.

Fuel charges for the Bon Air prototype will shrink from an estimated nearly 6,000 euros per year to 580 euros after the renovation, its architects say.

A major obstacle is the initial outlay, which has limited deep renovation to barely 1 percent of buildings per year versus a non-binding EU goal of 3 percent.

Those behind the Anderlecht project say the cost - which in this case includes extending the property, as well as insulation, a new heating system and new windows - is not the sole consideration.

Demolishing the houses and replacing them with zero-energy homes was not possible because the garden city estates are regarded as part of Brussels' heritage.

For VELUX of Denmark, which has teamed up with the Brussels civic authorities, it's the chance to deploy technology on a scale that makes it more competitive and to check it is user-friendly.

In return for financing the prototype, VELUX is allowed to monitor it for two years, once tenants move in sometime in 2017.

To quote the company's founder on the wisdom of testing theory - or EU policy - on real people: "One experiment is better than a thousand expert assumptions."

The International Energy Agency says making the relevant technology widely available and competitive will take a decade. As both a world leader in smart building and home to historic property that is the most wasteful on the planet, the EU therefore must forge ahead.

"The European Union needs to be pro-active in addressing deep energy renovation," IEA analyst Marc Lafrance said.

The potential losers are the utilities.

Sabine Froning, head of public affairs and communication at Sweden's Vattenfall [VATN.UL], said the company sought to become more of a service provider, while retaining a supply role, notably as a specialist in efficient district heating.

"A building is never going to be zero every hour of the day. It will always need to export and/or import energy," Froning said.

($1 = 0.8852 euros)