First view: a new angle to the Tate Modern extension

A plan for a glass ziggurat to house the £215 million extension to the Tate Modern has been dropped.

Under a radically revised design unveiled today, instead of a series of glass-covered cubes the new building will be a part-pyramid covered in a brickwork lattice. The brickwork is designed to make it greener, while vast oil tanks underneath the building are to be converted into exhibition spaces.

The changes, made in response to pressure from artists and Tate trustees, mean the gallery must reapply for planning permission from Southwark council, which approved the original idea last year. Tate director Sir Nicholas Serota called the initial designs "spectacular" and the scheme got a boost in December when ministers awarded it a £ 50million grant.

The new plans were drawn up by Herzog & de Meuron, the Swiss architects responsible for turning Sir Giles Gilbert Scott's original Bankside power station into the Tate Modern.

The most visible change is in the use of brick, in the shape of a perforated screen to allow light in and make the extension more heat-efficient. The extension, 11 storeys and 65 metres high, will increase Tate Modern's floorspace from 35,000 to 56,500 square metres.

Originally designed to cope with two million visitors a year, the gallery now has more than five million, which leads to crowding at weekends.

Two of the three oil tanks, 60 feet in diameter and 20 feet high, will be used to showart and will link to the Turbine Hall, with interconnecting spaces forming the backbone of the new Tate Modern. There will be two new public spaces: a square modelled as a city piazza and gardens for families and children.

The project is due to be completed in 2012. Apart from the government grant, the Tate has so far received £7million from the London Development Agency and £10 million from the private sector. More fundraising will begin in autumn.