In this video Jacques Herzog describes the concept and design process behind their design for the extension to the Tate Gallery in London. Here is the description according to the Tate Website:
As one half of architecture superstars Herzog and De Meuron, Jacques Herzog has been behind some of the world’s most spectacular buildings – from Beijing’s Olympic Stadium to the original Tate Modern nearly a decade ago. Plans are now afoot for an ambitious new extension to Tate Modern. TateShots was given privileged access to the architects’ studio in Basel, Switzerland, where work is well underway. In our film, Herzog talks about his excitement to be working on the project, and why TM2 (as the new building is currently known) will stand out in London’s busy skyline.
I haven't been to the Tate in almost 8 years now, but I recall being impressed by Herzog and de Meuron's tasteful adaptation of the old structure. Adding an extension is a difficult problem, especially trying to blend a bold new design with the historic image of the turbine hall. Their creative use of brick is elegant and admirable although I am not sure if the angular form quite fits into the context. However, I have loved almost every building of theirs that I have visited, so I will withhold final judgment until it is completed and I have seen it in person and in context.