Five new classrooms will be provided at the school in a £1.3 million eco-friendly development which will open in September.

It will include a green roof constructed from a grass-like plant which, with its run-off design, will allow rainwater to be collected and used for flushing the school's toilets.

Pupils at the school, in Wistow Way, Peterborough, cannot wait to start learning in their new extension, which is thought to be the area's best example of minimising a school's carbon footprint.

Managed by Peterborough City Council's property design and maintenance team, the project will replace three old mobile units and see a glass atrium fitted to the inner courtyard.

The green roof, which is constructed from a plant called sedum, will cover a waterproof membrane to give improved insulation and reduce the speed of rainwater run-off.

It will allow more rainwater to be collected and used for flushing toilets, reducing mains water consumption by 15 per cent.

The roof is also expected to improve air quality by absorbing carbon dioxide and releasing oxygen.

Year 4 pupil Lorcan Elliott (9) said: "I think it is great that the school is using environmentally friendly ideas in the new building.

"The under floor heating will stop heat loss, while the green roof will act as an insulator and help the sedum to grow.

"We are always being encouraged to think green, and are looking forward to using the new building after the summer holidays."

Headteacher Simon Eardley said: "The construction of the building has been a fascinating process and clearly demonstrates how all buildings can be designed to have a minimal carbon footprint. We hope this innovative approach will be replicated nationwide and become the standard to be imitated."

The new extension has also been fitted with a ground-sourced heat pump system, which will extract natural heat from the ground for use in under-floor heating.

The system, which received a Carbon Trust grant, is expected to cut running costs by 50 per cent compared with a conventional gas-fired boiler system.

Head of property design and maintenance with City Services at Peterborough City Council Robert Griggs said: "The installation of the roof marks a significant milestone in this project and, while some of this technology has been adopted in other buildings within the city, these features are now standard specification for the city council's in-house design team."

Green roofs were first used in Germany in the '60s.

More green ideas at school extension
Solar panels will pre-heat mains water to deliver a 10 per cent saving and light tubes will provide magnified natural daylight into some internal rooms.

The whole building will have high insulation levels and classrooms will have high level windows to optimise natural light and provide natural ventilation.

Photovoltaic cells will convert sunlight into electricity to power ventilation in the toilets and intelligent lighting controls will manage artificial light demand according to external light conditions.