Modelling thermal and humidity transfers within green roof systems: effect of rubber crumbs and volcanic gravel

ABSTRACT

The use of recycled materials and porous aggregates such as rubber crumbs and volcanic gravel (pozzolana) for the drainage layer can lead to improving thermal behaviour of the green roofs. On the other hand, the thermal performances of green roofs can be affected by the thickness of substrate and drainage layer. Therefore, the main objective of this study was to adapt modelling characteristics for different thicknesses of substrate and drainage layers used under constant and variable temperatures and solar radiation: specific rubber crumbs and volcanic gravel behaviour has been modelled. The simultaneous heat and moisture transfers within the green roof were estimated as well. According to the results, the 9 cm substrate was recommended to be used for the green roofs, once the thickness of drainage layer was 4 cm. Moreover, the optimum thickness of pozzolana and rubber crumbs as drainage layer was 6 and 7 cm, respectively, once the thickness of the substrate was kept constant (5 cm). By increasing the thickness of substrate and drainage layers, the fluctuation of internal ceiling temperature in the green roof models with the presence of humidity decreased, but not as much as that in the green roof models without the presence of humidity.

KEYWORDS:

• Modelling
• thermal behaviour
• relative humidity
• drainage layer
• substrate

Disclosure statement

No potential conflict of interest was reported by the author(s).

Additional information

Funding

This research was funded through the University of Liège (ULg) and ARC grant for Concerted Research Actions, financed by the French Community of Belgium, Wallonia–Brussels Federation (CityRoof project: Analogous green roofs for urban ecosystem services (2020–2023)).