Two eco-houses with bat boxes, wildlife ponds and wild flowers planted on the roof are to built in a back garden.

They are the latest examples of a new style of environmentally-friendly house-building which is becoming increasingly fashionable in Sussex.

The modern white cubes will be dropped a storey underground and floor-to-ceiling windows on the first level will let in more light and heat than in normal homes.

An energy-efficient boiler will be installed and used water will be channelled back into the bathroom to be reused when the toilet is flushed.

Developer Peter Brynin said: "The city needs more housing without a shadow of a doubt and environmentally friendly houses seem to be the way to go."

Mr Brynin, 57, is knocking down part of his house in Preston Park Avenue, Brighton, to make way for the three-bedroom houses.

He said: "Our children have grown up now and we don't really use the garden so we thought it would be lovely to have some houses there.

"Making the houses eco-friendly will cost a bit more but it is worth it."

John Turner, architect for the project, is close to completing a similar eco-house in the same road.

He said: "I think this is a cultural thing. People are becoming more aware of individual responsibility for the environment. It comes down to things like choosing your car wisely or using public transport and if there are opportunities to live in environmentally sustainable housing then that goes hand-in-hand.

"I think Brighton and Hove is a politically-aware city and there is more demand for this type of housing then there may be in other parts of the south."

An increasing number of eco houses are springing up around the county. Designer Duncan Baker-Brown won last year's Ibstock Downland Prize for best new build for his environmentally-friendly house in Windover Crescent, Lewes.

The ultimate eco-house was built by woodsman Ben Law, who built a house in Prickly Nut Wood, Lodsworth, using the trees around him and coppiced them so they would regrow.

Brighton and Hove city councillors unanimously gave the Preston Park project the go-ahead at a planning meeting yesterday.