London has never grown up. Unlike most major cities around the world, modern blocks of a mere eight storeys seem to dwarf the Victorian terraces that surround them. In the heart of the capital the complete redesign of the penthouse of such a block uses the benefits of its position to the full. The project - which involved the creation of a whole new structure - was the first, large joint commission for its architects, Ian Chee and Voon Wong, who were both born in Singapore and trained in London at the Architectural Association. The owner, an international businessman, had few specific ideas at the initial stage of the design process. "The client just asked us to come up with proposals," Chee recalls. "He didn't even tell us if he wanted two bedrooms, three bedrooms or whatever," adds Wong. "The brief was so open that it wasn't the easiest thing to do," concludes Chee. The first task for Chee and Wong was to rethink the space to create a greater feeling of structure and purpose. Now, looking in from the solid marble front door, the geography of the flat is clear. To the left of the entrance hall is the kitchen; to the right is a low and relatively dark wood-lined corridor, which contrasts with the wide space of the living area. This area, in turn, formerly an uncomfortable L-shaped space, is now welcoming and open, with expansive views out onto the surrounding rooftops. Initially, everything in the apartment had seemed low and flat; now the heights of the ceilings vary, helping to define the space and guide the eye through it. The dropped ceilings and raised voids also create a play of shadows that break up the otherwise monotonously dull plane of the ceiling. This goes to the core of their approach, the architects explain, finishing each other's sentences. "I guess we try to reorganise the space so that it's?" "Lucid?" "Clarity..." "...in the juxtaposition of the spaces, the feeling as you move through them from one to another." Different textures and finishes help to delineate the spaces even further: dark and warm aspen wood in the corridor, which adds to the drama of the light bedrooms, where Indian sandstone complements the grain of the American blackwood flooring. Light has played a great part in helping to shape the ambience, with indirect and concealed lighting creating a play of shadows on the walls. The need to bring natural light right into the heart of the flat has inspired the use of acid-etched glass for some internal walls. Space is enhanced by the choice of colour and finish - grey marble with reflective surfaces in the guest bathroom; pale green tones in the master bathroom - and by suspending wardrobes and beds just above the floor. Concealed fixtures throughout the apartment ensure that all lines are uncluttered. A temporary, disused structure that had previously been built on the roof has been replaced by a new room, which provides sweeping views of London's landmarks. This new space is reached by a spiral staircase - not Chee and Wong's original preference, but the only practical solution. An unexpected benefit was the effect on the main living area below of the natural light filtering from above through the newly opened-up roof. The construction of the staircase itself is unusual, with the stairs and balustrade made as a single free-standing piece. As Chee explains: 'The top balustrade is part of the staircase, so you read it as part of the structure, as though it was all dropped in, which it literally was - by crane!' The penthouse "box" has three seamless glass walls, which show off the panorama to the best possible effect. "We wanted the idea of a curtain - literally a sheet - of glass," say the architects. "The sheets are coated so that they cut down a lot of glare and heat. Light changes the mood dramatically: when it is dark outside the walls become mirrors." Careful thought went into the surrounding terrace garden. Since no permanent structure could be built, removable decking provided a practical and decorative solution. The plants were set into shallow trays - also easily removed - and are maintained by a computer-controlled irrigation system. At the end of an intensive six-month construction period the result is a unique home which has adapted a 1960s framework to new millennium style.