The London-based studio has completed the first stage of renovations at the Grade II*-listed Economist Plaza , adding a cafe on the ground floor and refurbishing six-storeys of the complex's tallest tower.
The Smithsons completed complex, home to the offices of The Economist Magazine for 52 years, in 1964.
Comprising three towers, of 15-, eight- and five-storeys, arranged around a raised plaza in Mayfair, the cluster of buildings are recognised as a significant example of the brutalist style.
The architectural pair went on to design social the housing complex Robin Hood Gardens in London's Poplar, which is controversially currently being demolished. The V&A museum acquired several chunks of the building, shipping some pieces over to Venice to display in an exhibition at this year's biennale.
Developer Tishman Speyer acquired the buildings in 2016 and appointed DSDHA to renovate them. The studio has previously worked on several other buildigns in the capital, including an apartment block in nearby Fitzrovia and a jewellery workshop near Tower Bridge.
Here, the brief was to emphasise the historic importance of the complex, while increasing its lifespan and making it more environmentally sustainable.
The renovated buildings have now been collectively renamed Smithson Plaza, in honour of the original architects.
"Having considered the impact of incremental changes since 1964, we have assessed what might be preserved and what can be changed," said Deborah Saunt, founding director of DSDHA.
"We have developed a phased restoration framework to create sustainable, flexible and contemporary workspaces whilst preserving public amenity.”
The 15-storey Economist Tower is renamed te Smithson Tower, and now features a 1,500 square foot cafe at plaza level.
Above, six floors have been delivered as part of the first phase of renovation works. Double glazing has been added to the windows, along with new lifts and amenities.
A planned 4,600 square feet of retail space will be added at street level, which the developers hope will be occupied by an art gallery.
The masterplan will gradually see all three of the buildings on the site renovated, accommodating the current tenants while staying true to the Smithsons' original vision. The Twentieth Century Society and Historic England have given their support to the proposals.
Several historic postwar brutalist buildings have recently been renovated, for instance, Richard Seifert's Centre Point Tower in London's West End has been transformed into apartments by Conran and Partners.
Elsewhere in the UK, the BDP-designed Preston Bus Station has just been restored and modernised by John Puttick Associates.
Photography is by Grant Smith.