Eleven storey glass extension will add 60% more space to the museum and will open by 2012

London’s Tate Modern has announced plans to build a £215m glass extension.

Designed by architect Herzog & de Meuron, the 11-storey building will add 60% more space to the museum to accommodate the 4m visitors the gallery receives each year.

The 23,000 m2 space will house several galleries and performance zones, as well as cafes, shops and offices.

It is hoped the extension, which will be funded by private investors and grants, including £7m from the London Development Agency, will be open in time for the Olympics in 2012.

The design is the latest by Herzog & de Meuron, who converted the Bankside power station into Tate Modern in 1995. The firm also designed the Olympic stadium in Beijing.

Architect Jacques Herzog said the extension was a ‘unique opportunity’ for the firm.

‘We don’t have a strategy to make it a spectacle, we just tried to discover what made sense [for the Tate],’ he said.

‘We are at a different point of our career [from when we first converted the power station]. It’s a unique opportunity to work on the same building at a different point of our lives.’

Tate director Sir Nicholas Serota said the extension would be a ‘counterpart’ to the Olympic developments in East London, as well as creating a cultural quarter in London.

The tower will be subject to planning approval later in the year.