German architecture studio Demo Working Group has removed all non-structural walls from this 1970s high-rise apartment in Cologne, creating a utilitarian open-plan interior.

Named Kier after its address on Kierberger Straße, the apartment is set in a housing block built in 1972. Before the renovation, wallpaper covered its concrete shell and a myriad of dividing walls created dark, enclosed rooms.

Now, a structural concrete wall in the middle of the floor plan is the only interior wall that remains, although Demo Working Group used a concrete saw to cut out a doorway and create a direct link between the living space and the bedroom.

"We were interested in how these concrete structures can be transformed to enable new spatial options," partner Matthias Hoffmann told Dezeen. "The new opening between the living and the sleeping area redefines the circulation in the apartment."

Raw concrete perimeter walls work together with the remaining central wall to create an industrial-looking backdrop, consistent throughout all areas of the apartment.

"The high-rise structures of that era are typically built out of concrete," the studio said. "We took off the wallpaper so that the building's structure with its specific texture and character can be experienced inside the apartment."

The newly liberated interior benefits from having windows on two sides, which the designers capitalised on by employing translucent, transparent and reflective surfaces throughout.

Former internal walls were replaced with sheets of transparent and frosted glass, allowing light to penetrate further into the space and providing a contrast with the heaviness of the concrete.

This creates a free-flowing atmosphere in the space, which almost functions as a studio apartment as a result of the minimal, see-through divisions between the living space, kitchen, bedroom and bathroom.

Mirrors and reflective surfaces are applied to other spaces, too. In the kitchen, cupboards are tucked below a window that casts light onto a full-height mirrored backsplash on one side.

The green kitchen counter also reflects light and is made from a heavy-duty plastic, which Demo Working Group says is usually reserved for use in laboratories.

Glossy white tiles line the kitchen and bathroom area while a built-in storage unit in the living space is clad in sheets of aluminium to level up the brightness of the interior.

Furnishings follow a colour palette of blues, greens and purples, with the sofa and window frame in the living area picked out in a deep blue, referencing the accent colour found throughout the wider apartment block.

Metal continues to feature in the furniture and fittings, from the legs of the dining set and bookshelf to a horseshoe-shaped light fixture on the bedroom ceiling.

Demo Working Group was founded in 2019 and works on architecture and interior projects throughout northern Germany.

Other apartment interiors that have recently been featured on Dezeen include a refurbished art deco-style apartment in Milan and a flat in Kyiv that features colourful furnishings and glass bricks.

The photography is by Jan Voigt.