The decision to build a third greenhouse follows the popularity of the scheme, which has surpassed expectations. The Eden Project firm originally expected 750,000 visitors a year when it opened in March, but that figure has now been raised to 2 million.
Further extension plans include an education resource centre, a hotel and a conference centre. The education centre and hotel will be designed by Nicholas Grimshaw & Partners.
The new 10,000 m2 biome will stand on its own at the southern end of the site, next to the ornamental lake. It will include plants from Mexico, Namibia and Botswana. Work is not due to start on site until at least next year, according to project team members.
Keith Titman, deputy project manager of the Alfred McAlpine/Sir Robert McAlpine joint venture that built the original centre, said the scheme would be similar in style to the first. He said: "It certainly has the same sort of flavour as the existing biomes."
A funding document is currently being put together for the extension and a source close to the project said businesses were keen to support it. He emphasised, however, that the Eden Project believed that any backer must be sympathetic to the wider aims of the scheme.
An application for planning permission for a £1.5m educational resource centre has been submitted. If accepted it will be sited to the south of the warm temperate biome.
A feasibility study is also being carried out for a 200-bed hotel by QS Davis Langdon & Everest. Outline planning permission is being sought to site the hotel on the rim of the clay pit at the southern end of the site. Work on the original project began on site in late 1998 following a lottery grant of £43m.