Triple Towers, Sofia

Triple Towers – Sofia, Bulgaria
Project overview

The Triple Towers project comprises high‑rise towers for pharmaceutical companies Sopharma and Litex in Sofia. The buildings provide offices and laboratories and are recognised for their high daylight quality and sustainability. The towers were designed to achieve BGBC and DGNB Gold certification, reflecting their advanced environmental performance.
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Design challenge

Sofia’s continental climate features strong sunlight and cold winters. The towers’ deep floor plates required daylight to penetrate up to 10 m into the interior to reduce reliance on artificial lighting. At the same time, the façades had to achieve a very low solar heat‑gain coefficient (around 0.05) and prevent glare for occupants working at screens. Achieving these goals with conventional shading would have been difficult.

RetroSolar strategy

The towers use a double‑skin façade with RETROLux louvers featuring high reflectivity (approximately 95 %) and a visible transmittance of 78 %
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. The retro‑reflective louvers are positioned to send direct sunlight back towards the sky and redirect 3 % of the remaining light onto the ceiling
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. This ensures a deep, uniform distribution of daylight. The double‑skin system also allows natural ventilation, further reducing energy consumption.

Building physics and performance

The reflective louvers drastically reduce solar heat gain, achieving an SHGC of around 0.05 while maintaining high daylight transmission. The resulting interior spaces have a high colour rendering index (around 96 %), meaning that colours appear natural under the daylight. The system provides daylight autonomy up to 10 m from the façade, reducing the need for artificial lighting. The building’s energy consumption for cooling is significantly reduced thanks to the shading and ventilation strategy. The combination of high reflectivity and clear glazing creates bright, comfortable interiors.

Architectural outcome and significance

The Triple Towers stand as a benchmark for sustainable high‑rise design in Eastern Europe. The use of RetroSolar technology allows the towers to project a transparent and modern appearance while meeting strict energy targets. The deep daylight penetration enhances occupant wellbeing and productivity, making the buildings attractive to tenants. The project underscores the capability of mirror‑optic louvers to deliver both aesthetic and performance excellence in tall buildings.