 Some easy measures will make you greener and save you money: laying down more insulation in the loft and putting panels behind radiators on external walls.  But as you follow the hints you are likely to start wondering: when will all homes automatically be built in a planet-friendly way that's also kind to the wallet?  In Kettering, Northamptonshire, outline planning permission has just been granted for a 5,500-home eco scheme, which will also include new schools, offices and transport improvements. Kettering Council is keen that the developers, Bee Bee Development and Buccleuch Property, consider CarbonLight homes, designed by HTa architects, as green housing for the mass market.  Some prototypes have already been built on the site. My wife, son Freddie, daughter Jemima and I spent the weekend in one of the CarbonLight four-bedroom semis to test the experience.  as we discovered, this was authentic eco-living, complete with grey water harvesting, by which water from showers, baths and washing machines is recycled to flush lavatories. Paul Hicks, CarbonLight's design and construction co-ordinator, enumerates the home's green credentials: "The houses are largely energy self-sufficient, using solar heating combined with air-to-water heat pumps for hot water and space heating, and natural ventilation for cooling. as a result, fuel bills are expected to be at least 70 per cent less than the average for a similar-sized new home."  The first striking point about the house is the number of windows. Velux, the window giant, is very involved in the CarbonLight project. Plenty of windows means plenty of natural daylight, another thing that saves on energy bills. The houses are part of Velux's Model Home 2020 initiative, based on the European Union energy policy to reduce total energy consumption and CO2 emissions by 20 per cent by 2020, with 20 per cent of energy consumption to come from renewable sources.  Inside the house, a climate-control system opens and closes all the windows, blinds and shutters automatically when the weather changes.  Before long Freddie, 5, who has enough energy to power 5,500 new homes east of Kettering, was playing with the WindowMaster system and calling himself a WindowMaster Jedi knight.  a building management system monitors the temperature and ventilation levels in every room along with solar energy and heating and water consumption. The open-plan design, which includes a triple-height atrium, produces a natural "stack" ventilation effect, which allows fresh air to move in and replace stale overheated air.  During our mild winter sleepover the house temperature hovered at about a comfortable 20C, but should the outside temperature have plummeted,the wood-burning stove in the living room had "Plan B"' written all over it.  The drawbacks were the need to dance around in the shower in order to get wet and the fact that I had enough time to sink a bottle of wine while running the water for the kids' bath - the hot water courtesy of the solar system. During supper the lights in the dining area kept going out as they responded to body movement. Romantic mood lighting is one thing, but pitch darkness is another.  In March two families will move in to a pair of semi-detached CarbonLight homes and live rent-free for a year to monitor long-term the carbon emissions, water use and air quality of the properties before they are sold on the open market at an estimated price of between ?275,000 and ?300,000.  CarbonLight homes aim to reduce onsite carbon emissions by 80 per cent, with the other 20 per cent to be offset by making energy-efficient improvements to council homes in the borough - so in effect the homes are carbon neutral. Velux believes that CarbonLight will conform to level 5 of the Code for Sustainable Homes - the likely future carbon compliance level. It currently stands at level 6.  Hicks says: "CarbonLight, rather than the specific architecture or build solution, provides the basis for a viable  