BOB AG - Airport City, Düsseldorf

BOB Balanced Office Building – Germany
Project overview

BOB (“Balanced Office Building”) is a family of sustainable office developments pioneered by BOB AG across Germany. Each BOB building follows a holistic energy concept that targets low operating costs, high occupant comfort and DGNB Gold certification. The concept emphasises balanced proportions of glazing and opaque surfaces, thermal mass for passive cooling, and advanced daylighting strategies. BOB buildings are typically mid‑rise and are designed to be replicable across different sites.

Design challenge

Typical office buildings require external blinds or louvers to prevent overheating, but such systems are exposed to wind and weather and demand regular maintenance. BOB AG sought an interior shading solution that would offer comparable performance while reducing construction complexity. Additionally, the daylighting strategy needed to complement the building’s passive cooling system, which uses water pipes in the concrete ceilings to absorb and dissipate heat.

RetroSolar strategy

Interior RETROLux 75 mm blinds are installed behind the façade, spanning from floor to ceiling
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. The slats have a reflective upper surface that acts as a light shelf, bouncing sunlight onto the ceiling, while the lower surface remains translucent to maintain outward views. The blinds are manually operable via a hand crank, allowing occupants to fine‑tune glare control without complex automation. This simplicity reduces the risk of malfunctions and minimises maintenance. The blinds work in tandem with the building’s window‑to‑wall ratio (~50 %), which is optimised to provide sufficient daylight while limiting solar gains
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.

Building physics and performance

The reflective slats minimise solar heat gain by sending direct sunlight back towards the exterior, while the remaining diffuse light is redirected onto the ceiling. This results in a bright yet glare‑free interior with daylight reaching up to 5–7 m from the façade. By reducing the reliance on exterior shading, the façade remains clean and unencumbered by moving parts. The internal placement of the blinds also protects them from wind and weather, leading to lower maintenance costs over the building’s lifespan. The integrated cooling in the concrete ceilings further moderates temperature swings, enabling the building to operate with minimal mechanical cooling.

Architectural outcome and significance

The BOB Balanced Office Buildings present a coherent architectural language characterised by rational façades, generous daylight and comfortable interiors. The use of RetroSolar blinds underscores the developers’ commitment to durable, low‑maintenance solutions that prioritise user comfort. The success of the BOB concept has led to its replication in multiple German cities, demonstrating that energy‑efficient commercial architecture can be both cost‑effective and pleasant for occupants. By providing a replicable model, BOB supports the wider adoption of mirror‑optic shading technology.