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Passive Cooling Double-skin roof
The developed double-skin roof system consists of an air cavity separated by two elements, allowing airflow to be induced using a fan system to dynamically dissipate the heat stored in the roof’s thermal mass. A 56mm-thick air cavity is created using a ribbed metal panel, protected thermally and mechanically by a multi-layer skin of insulation and lightweight concrete. This double-skin roof solution adopts a pre-industrialised concept that is adaptable to various roof configurations, utilising available commercial air ducts, evaporative fan units (Biocool units), skin roofing and smart control solutions. This solution features a plug-in characteristic, enabling easy integration without visual impact or significant changes to the architectural building design, with an implementation cost of 98 €/m2, which represents only an additional cost to a conventional roof solution of 31 €/m2.
Integrating this solution in naturally conditioned residential buildings could reduce instances in which indoor conditions exceed the upper comfort threshold of the ASHRAE adaptive comfort 90% acceptability range to only 3.4% of the summer period, with a maximum daily discomfort of 13%. Achieving such a comfort level in summer 2025 resulted in an average water consumption of 90.3 L/(day∙100m2) and electricity consumption of 4.7 kWh/(day∙100m2), representing an operational daily cost of ~1.2€/(day∙100m2).
This solution was applied in an existing building in Seville as part of a renovation strategy to reduce overheating events. The experimental results indicate that integrating a double-skin roof system utilising night ventilation and evaporative cooling in warm climates will benefit existing and new buildings alike as a resilient thermal envelope solution. Additionally, the double-skin roof can yield interesting results in commercial buildings, as the main effect of the cool ceiling is concentrated during daytime hours, which are peak occupancy times in summer. The key feature of this roof solution is its plug-in characteristics and the possibility to reduce, or even neutralise, the building's cooling demand using nature-based solutions.
