Wallisellen, Zurich

Wallisellen/Bluewin Tower – Zurich, Switzerland
Project overview

The Bluewin Tower, formerly a telecommunications headquarters, stands in the Zurich suburb of Wallisellen. Architects Heinz Zimmermann and Michael Wirth Architects refurbished the building in the early 2000s to create a modern office tower with improved energy performance. The project built upon Zimmermann’s experience with non‑ventilated double‑skin façades (Closed Cavity Façade) previously developed for a mail distribution centre in Wädenswil
retrosolar.us
.

Design challenge

The refurbishment had to upgrade the building’s thermal performance without increasing its weight or altering its external appearance dramatically. The existing façade lacked effective solar control, leading to overheating and high cooling costs. Zurich’s climate features significant seasonal variation, so the façade needed to perform well in both summer and winter. The non‑ventilated cavity had to be sealed to prevent condensation and maintain clear views.

RetroSolar strategy

Initially, Zimmermann utilised RETROLux A louvers in the Wädenswil mail distribution centre. For the Bluewin Tower he selected RETROFlex louvers because of their high visual transmission and low solar heat gain
retrosolar.us
. The louvers are placed horizontally within the closed cavity façade, remaining largely invisible to occupants. Low‑iron glass is used on the outer pane to maximise daylight transmission, while the inner pane provides insulation. The retro‑reflective louvers reflect sunlight outwards and reduce internal heat gain.

Building physics and performance

The closed cavity façade combined with retro‑reflective louvers delivers low SHGC values without the drawbacks of tinted glass. The absence of ventilation in the cavity eliminates the need for moving air and reduces mechanical complexity. The reflective louvers maintain views while providing effective shading. The system reduces cooling loads in summer and retains heat in winter, contributing to the building’s improved energy performance and occupant comfort.

Architectural outcome and significance

The Bluewin Tower refurbishment demonstrates how existing high‑rise façades can be upgraded using RetroSolar technology without major aesthetic changes. The closed cavity façade provides a clean, continuous exterior, and the retro‑reflective louvers are nearly invisible. The project influenced subsequent high‑rise renovations in Switzerland and established the viability of closed cavity systems with integrated shading for improving energy performance.