Blue-green roof heat transfer modeling in drought conditions

Žižak, Tej (author), Medved, Sašo (author), Arkar, Ciril (author)

This study presents a comprehensive numerical heat transfer model for a novel green roof system with water storage layer (blue-green roof). The experimental validation over a two-month period included 15 days of water stress conditions and validation of temperatures across layers, evapotranspiration (latent heat flux) and water balance based on water level measurements. A key focus is on the effect and modeling of the air gap within the water storage layer and the accurate prediction in water stress conditions. Different approaches to modeling are evaluated, and a detailed method with separate modeling of convective and radiative heat transfer within air gap is proposed, which improves the accuracy of surface temperature above air gap prediction with normalized mean error (NRMSE) of 6 %. Additionally, the role of convective heat flux in drought conditions is analysed. With incorporation of stabilization correction factor into the aerodynamic resistance model, normalized error of substrates surface temperatures was reduced to 6.1 %. To realistically simulate the water balance and distribution across layers, a water extraction coefficient was introduced, quantifying the portion of water for evapotranspiration taken directly from the water storage layer. For the studied blue-green roof with mineral, organic substrates and sedum under the site conditions of this experiment, the calibrated water extraction factor was KZ = 0.22. The proposed model provides a mean to predict the heat transfer of sustainable roof system adapted to increasingly frequent dry periods and extreme weather events.

• Language: English
• Keywords: green roof, water storage, evapotranspiration, heat transfer, air gap
• Work type: Article
• Typology: 1.01 - Original Scientific Article
• Organization: FS - Faculty of Mechanical Engineering
• Publication status: Published
• Publication version: Version of Record
• Year: 2026
• Number of pages: 16 str.
• Numbering: Vol. 288, art. 113957
• PID: 20.500.12556/RUL-176041
• UDC: 536.24
• ISSN on article: 0360-1323
• DOI: 10.1016/j.buildenv.2025.113957
• COBISS.SI-ID: 257737475
• Publication date in RUL: 19.11.2025

Record is a part of a journal

• Title: Building and environment
• Shortened title: Build. environ.
• Publisher: Elsevier
• ISSN: 0360-1323
• COBISS.SI-ID: 4318474

Licences

• License: CC BY 4.0, Creative Commons Attribution 4.0 International
• Link: http://creativecommons.org/licenses/by/4.0/
• Description: This is the standard Creative Commons license that gives others maximum freedom to do what they want with the work as long as they credit the author.