The Ecology Building Society has started laying the foundations for its new £950,000 head office in Silsden.

The building, which is being built by Otley-based Lotus Construction, aims to showcase the environmental principles of the country's youngest building society.

The 205 metre-long site lies above the Airedale flood plain to the south east of Silsden town centre, on the Belton Road Industrial Estate.

The building will only occupy a small part of the site, which includes mature trees and a community garden area with dog walking facilities.

The company, which was set up 21 years ago in Cross Hills, Keighley, promotes the concept of sustainability through its mortgage lending. It also provides a range of ethical savings schemes.

To coincide with these principles, a level of sustainability had to be achieved in the new building, which was designed by Mark Hodson of Hodson Design of Grimsby.

Wherever possible, use has been made of traditional materials such as rendered straw bales, stone and timber.

There will also be a planted nature roof, and systems will be put in place for rainwater harvesting.

A heat exchanger will recover waste heat from equipment and people, while energy for the premises will be supplied by a combination of 'photovoltaic cells' and 'green electricity' from the Society's current supplier Ecotricity.

The firm also wants the new building to be used by members of the local community. The meeting room, which will be made from a circular rendered straw bale structure detached from the main building, will be made available to local community groups and schools.

The premises will also house a study area and library specialising in 'green' issues, which the firm says it will let others use.

Gus Smith, The Ecology Building Society's chairman, said: "The new building is a major milestone in our evolution from a small group of concerned ecologists with reserves of £5,000, to one of the fastest growing building societies, with assets now exceeding £42 million.

"The new building showcases what is important to us in terms of sustainability and active community development."