Chinese architecture studio Neri&Hu sliced away the rear wall and replaced it with glass for this renovation of a 1930s townhouse in Shanghai.

The three-storey building is located in the Tianzifang district of the Chinese city, where it originally functioned as a house for a single family. Neri&Hu's redesign converts the building into three divisible apartments, each with a combined living and dining room at the back and a bedroom at the front.

A bulky metal staircase replaces the old timber steps that previously connected the floors. Sandblasted glass (completed after photography) separates the stairway from the corridor of each apartment so that residents can see the outlines of neighbours passing by.

A 45-degree skylight brings daylight into the stairwell, while a shared laundry room and terrace are positioned at the top.

"The blurring of both the private and the public acts as the central concept that binds the split level together, and at the same time, bring life to the middle and darkest portion of the house," says Neri&Hu.

The building is arranged over split levels, so the architects have also inserted a second set of stairs within two of the apartments. Unlike the main staircase, both are constructed from timber to match the flooring.

Bathrooms stretch along the southern side of each apartment and are enclosed behind another layer of sandblasted glass. Showers feature a west-facing window, offering a view down into the shared lobby below.

New windows were added to both the front and rear elevations, while the rest of the exterior has been coated in black paint. "The colour black was selected to make the building disappear," add the architects.

Although the building was designed for three separate tenants, it is currently being used as one large house.

Lyndon Neri and Rossana Hu have worked on a number of renovation projects in Shanghai, where their studio is also located. Past projects include a design gallery in a former colonial police station and a hotel in a disused army headquarters building, which was the overall winner at the inaugural Inside awards in 2011.

Dezeen interviewed the architects in November, when they told us that Chinese architects need to develop their own design manifesto to stem the tide of "half-assed" building projects in the country. See more stories about Neri&Hu on Dezeen.

See more recent architecture in China, including an asterisk-shaped restaurant and winery near Beijing.

Photography is by Pedro Pegenaute.

Here's a project description from Neri&Hu:

Rethinking the Split House

The magical lane houses, which were once the dominant fabric that made urban Shanghai the intoxicating place that it was in the 1930s, are now slowly being demolished, taken over by high-density developments all over the city. Neri&Hu was commissioned to reconstruct a dilapidated lane house left with almost nothing except its glorious shell in the historic and artistic Tianzifang area in Shanghai, and the mission was to transform it into three separate apartment units.

Neri&Hu's strategy was to rethink the typology of the lane house - keeping the split level formation, a typical trait to lane houses in this city, and add spatial interest through new insertions and skylights to accentuate the architectural integrity of such a typology, contemporising it for today's lifestyle.

Historically the lane houses are separated with two distinct spaces - a longer and often rectangular space with a smaller room half a level above that creates a split section connected by a winding stairway in between. These lane houses which were often occupied by single families during the turn of the century, have changed over the course of the city's economic history. They are now typically occupied by three or more families, sharing the public staircase and landings, so that neighbours living on different levels or rooms have a chance to interact as they move in and out of their personal units.

To keep the spirit of this typology alive, a new continuous metal stair was inserted to replace the old decaying wooden stair that was not to code. It also serves to act both as a vertical connection to the three levels and at the same time a lock for the frontal room and room half a level above to be intact in its configuration. To keep these spaces pure and rigorous, all toilets were inserted into the stair spaces. The bathrooms, conceivably the most intimate spaces of each apartment, are inserted next to the most public stairway separated only with a sandblasted glass divider. Above this stairway, a clearstory skylight was added to bring light to the darkest space and also to the frontal room, the room half a level above, and the staircase space itself. The blurring of both the private and the public acts as the central concept that binds the split level together, and at the same time, bring life to the middle and darkest portion of the lane house.

Architecturally, the decorative elements added over the last 60 years were stripped off, and large openings were created on the frontal section to improve light qualities to the public spaces of each apartment. The colour black was selected to make the building "disappear", in hoping that one would experience the split-section connected by a public stairway that is so vital to Shanghai's urban life in the 30s. By capturing the spirit of the historic past and making new abstract insertions to meet modern needs, Neri&Hu infused life into a lane house in a neighborhood whose original fabric is dissolving too fast, too soon.