Unicredit Tower

Milan, Italy

Studying stack effect to ensure safe conditions in Italy’s tallest building

Porta Nuova is the main business district in Milan. In the heart of this district is Porta Nuova Garibaldi, a masterplanned development consisting of three skyscrapers; the largest of these, Unicredit Tower, is the tallest tower in Italy at 231m. 


  • The Challenge

    The design team recognized that one potential concern with Unicredit Tower was stack effect. Common in tall buildings, stack effect is caused by differences in relative heat and humidity inside and outside a structure; the intensity of the effect can vary with the seasons and according to a building’s systems and design.

    Stack effect’s central feature is the movement of warm air up through the building; left unaddressed, this movement can have a range of unwanted results, including problems with the operability of elevators and doors. The tower’s design team approached RWDI for analysis that would help them ensure that stack effect would not make it difficult for the building’s doors to open during cold weather. Stubborn doors are generally undesirable, but when it comes to emergency exits, operability issues can present major safety concerns. The designers needed to be totally confident that the exits would be functional during all seasons and conditions.

  • Our Approach

    We analyzed the design of the building, looking specifically at the locations of the emergency exits. RWDI has conducted stack effect studies on a wide range of buildings in diverse climates – and our experienced team recognized after a brief review of the designers’ drawings that the doors in question, which opened outward, would indeed be subject to additional pressure due to stack effect. Our next step was to develop a numerical model that would quantify the pressures on the doors and answer the designers’ question as to whether the pressure was enough to cause a safety concern.

    Our team studied the full range of interior and exterior conditions that would affect the doors – considering seasonal fluctuations in temperature and the local wind environment. Once we’d generated a detailed picture of the pressures the doors would experience, we compared these to the building code standards. In the end, we were able to assure the project team that no significant design modifications were needed in order to ensure acceptable performance of the emergency doors. We proposed a simple, low-cost and easily implemented plan for emergency situations that would ensure occupants could exit safely when they needed to.

  • The Outcome

    Unicredit Tower opened in 2012 and has been operating successfully since that time, becoming part of a thriving mixed-use neighborhood with restaurants, shops, offices and vibrant public spaces.