When the developer Seaforth Land bought the building in 2018, however, it was badly worn, technically outdated, and cluttered with later accretions like partitions and bulky mechanical equipment. Squire & Partners stripped Space House to the bones and refitted it for multi-tenant occupation. The firm’s intent was to reveal the building’s obscured geometries and ensure that any additions were true to the original. But this required what project director Tim Gledstone calls “investigative archaeology.” Many original drawings had been destroyed, sending the project team to search for records in private photographic collections while looking for clues on-site like an undocumented staircase rising from the foyer.

Squire & Partners’ most significant alteration remedies a defect born of use. Bulky air-conditioning equipment that accumulated on the roof has been replaced by two additional stories, reinstating the crisp silhouette that Seifert intended. As the building is now protected, the extension required careful negotiation with heritage authorities.

The new 16th floor is faced in an extra ring of color-matched concrete cruciforms. Looking up, the surgery is imperceptible. To avoid an unsightly elevator overrun, terrazzo stairs complete the journey to the new 17th story, a glass-walled aerie encircled by a terrace. Air-source heat pumps are discreetly concealed above.

At ground level, a mezzanine has been stripped away to restore visibility through the tower’s capacious double-height foyer. Long views through the complex evoke the light and space once promised by lifting buildings off the ground. The landscaped piazza is now a pleasant place to linger, which is encouraged by a glass-walled café below a frilly concrete canopy that projects from the tower and originally sheltered a gas station for tenants. In another sign of changing times, basement parking has been reinvented as exhibition space, bicycle storage, and tenant showers and locker rooms.

The architects also took cues from Seifert’s building and its era for the interior design of shared spaces. “It was a bit monochrome,” says Gledstone, “and we wanted to introduce some of the color and optimism that followed the austerity of the midcentury.” Furniture in the plant-filled foyer includes original Zanotti sofas, and a vintage turntable plays sounds of the 1960s. The tower’s material palette is picked up in terrazzo floors, a ribbed reception desk in speckled concrete that looks almost edible, and even micro-fluted concrete panels on the walls of elevator cars. “This was never going to be a vanilla building,” says Gledstone. “So we could keep adding chocolate sauce.”

On the upper floors, extra space was created by infilling redundant vertical shafts originally required to induce natural cross-ventilation. They now form meeting rooms clustered around the central elevator bank, while broad passages in between lead to the donut of open-plan workspace on the perimeter. Suspended ceilings were stripped out to reveal coffered concrete slabs, with slender downstand beams radiating from the core like the spokes of a wheel. Here, the concrete is workaday, with scraps of plywood formwork embedded in the material. They make a touching connection to the handwork of builders in this supposed product of the space age.

Gledstone imagines that Seifert might have exposed the soffits, if the technology of the time had allowed the neat integration of mechanical and electrical equipment. Even today, finding a workable, high-performance solution eluded the first engineering team. With another, Squire & Partners developed bespoke “micro chilled beams” that run between the closely spaced concrete downstands and use water rather than forced air to deliver cooling. The costly exercise reflects the client’s determination to have the first protected building of its age with an “Outstanding” sustainability rating under the BREEAM assessment method. (Other contributing factors include retaining existing structure, solar shading from the deep facade, and even high-level holes for nesting birds.)

Replacing every window to improve thermal performance was another major challenge, as the architects found significant variance in the openings. “We had to 3D-scan the whole structure and make six window sizes, with a frame detail that could mitigate extra differences,” says Gledstone. The original window units had cement board bottom panels, which were replaced with laminated glass with a mesh interlayer that preserves a solid outward appearance while increasing light levels inside. Floor-to-ceiling glazing, working with the curvature of the facade, now emphasizes exceptional views in every direction, revealing a continuous, lively urban jumble rather than a collection of orthogonal slices. “It’s somehow much more human to be in a round space than a square one,” says Gledstone.

In this robust but comfortable observatory, the confident and sophisticated character of the original building is newly apparent everywhere, from wayfinding signage that picks up on its geometries to the raw concrete backs of the cruciforms. Richard Seifert would feel right at home—and perhaps vindicated.

Seifert led one of Britain’s most prolific practices, responsible for some 500 projects built between the end of World War II and the early 1980s. To the public, however, he was controversial, his structures representing the cavalier erasure of treasured streets during the postwar building boom. (Space House itself replaced the Magnet House, an Edwardian building completed in 1921.) Other architects also viewed him with suspicion. At a time when the profession valorized state-funded work in public housing and education, Seifert specialized in the low-status field of commercial development.

But time has been kind to Seifert, and Squire & Partners’ successful renovation is a big step forward in an ongoing reassessment of his work. A 1968 critic admitted that had Space House been built in Los Angeles, its quality might have been better understood. At a distance of decades, and with a helping hand, it’s now hard to miss.