The original glass proposals were awarded planning permission in March 2007. Structural consultants Ramboll Whitbybird were appointed to the Herzog & De Meuron led design team in February this year.
The Tate museum said that a number of changes have been made to the design in response to a revised brief and consultation with artists and curators.
At the heart of the updated plans are the oil tanks of the former power station which will be retained as spaces for art and from which the new building will rise. In the previous scheme the oil tanks were occupied by an auditorium and other facilities.
The oil tanks lead directly into the Turbine Hall and these interconnecting spaces will become the foundation of the new Tate Modern.
This closer relationship between the buildings is also expressed in the façade; a perforated brick screen through which was the building will glow at night.
The building is more compact than in the previous scheme which built up of stacked boxes and the configuration is more flexible to allow for future changes in the programme.
The new building rises 65 metres above ground in 11 levels and will add an additional 21,500 sq metres to Tate Modern's existing 35,000 sq metres. A sweeping ceremonial route rises up through the floors providing a connecting path through the galleries and offering stunning views over London.
Overall the project will also address some of the strains on the current building. The gallery was originally designed for 2 million visitors. With current visitor numbers exceeding 5 million, there is serious overcrowding particularly at weekends. Changes in contemporary art practice mean that different kinds of spaces are required and additional space is needed so works can be brought out of storage and shown on a more permanent basis.
The project is due to be completed in 2012 at estimated cost of £215 million at 2012 prices. To date Tate has received £50 million from Government, £7 million from the London Development Agency and £13 million from the private sector towards the overall costs.