Spanish studio Office for Strategic Spaces has refurbished a 19th-century housing block in Barcelona, unlocking a previously neglected yard space with a new public courtyard linked by criss-crossing metal walkways.

The block, called La Carboneria, sits within Barcelona's Eixample district, known for its famous gridded urban plan designed by Ildefons Cedrá.

During the design of the housing block, its location was subject to plans by the city to cut through the district with large, wide boulevards, similar to the urban plans implemented in Paris in the middle of the 19th century.

When plans for some of these grand boulevards were scrapped, La Carboneria was left with a "ghost facade" that was later enclosed by new buildings to form a dark, triangular courtyard at its rear.

Madrid-based Office for Strategic Spaces, led by architect Ángel Borrego Cubero, was tasked with reconfiguring the somewhat awkward urban condition of the apartment block, which had been left empty following the eviction of squatters in 2014.

"[The original architect] was forced to plan facades to all four sides of the building, unsure where the main streets would be and which one his building would face," explained the practice.

"Over a century and a half later, the facade that faced the never-built boulevard had to be recovered, its larger windows unblocked, even if they now overlooked two intersecting party walls instead of Barcelona's version of the Champs Elysées," it continued.

Creating a new public space at the rear of the building, the block's stairwell and lift core was relocated out of the building and connected back into the newly opened facade by metal walkways.

This organisation creates a new double-aspect condition for the flats that now face the public courtyard to the rear and the street at the front. A bathroom and storage block aligned with an existing load-bearing wall sits at the centre of the building.

"The building seems to have been turned inside out. Its most striking facade is hidden inside a triangular courtyard and, to make it accessible, its stairwell and elevator have been moved from the inside of the building to the furthest corner of this patio," explained the practice.

"The walkways that join both elements make the patio work as a surprising, tridimensional public space for the neighbours," it continued.

As much as possible, the original structure of the apartment building was retained and reinforced, with only the roof needing replacing.

Inside the apartments, traces of the old building – such as wood beam ceilings and exposed brick walls – have been refinished and painted. These are juxtaposed against contemporary elements including wooden panelling and brightly tiled floors in the kitchens.

"Although the heritage regulations applicable allowed us to gut out the entire building except the facades, the original structure of the building was preserved as much as possible," said the practice.

Other renovation projects completed by Office for Strategic Spaces include the transformation of a former industrial building in Madrid into a workspace for creative startups.

Elsewhere in Barcelona, Parramon + Tahull renovated an apartment in the city's Gracia neighbourhood and added birch plywood joinery and ceramic tiling

The photography is by Simona Rota.