Urban Materials for Cool Cities – UMat4CC

To answer these questions, the UMat4CC project aimed to provide tools and knowledge to assist urban stakeholders in devising and deploying urban cooling strategies suited to their urban context. It specifically focused on the thermal and climatic behavior of rooftop structures with internal or external thermal insulation, standard and cool (reflective) surfaces and rooftop watering. In addition, the project also focused on designing a simplified model of urban overheating with geospatial information systems frequently and easily used by urban stakeholders.

The first axis relies on an experimental platform for the thermal characterization of materials (conductivity, specific heat, albedo, …) and the behavior of real roof structures under heat-wave conditions (climate chamber, …). The second axis relies on the analysis of overheating risk combined with a simplified physical indicator of pedestrian heat stress: the urban cooling potential (UCP).

The lab study of roof structures showed that internally-insulated roofs contribute least to ambient air heating during the day, but contribute most to the UHI effect, i.e. the opposite of externally-insulated roofs. Rooftop watering can eliminate these effects once a threshold watering rate has been reached which depends on roof structure and reflectivity. The cool externally-insulated roof has the lowest optimal watering rate at which these contributions are canceled out. Analyses of UCP data showed that it is able to identify the principal hotspots of a given site or area.

Several scientific articles (3) and conference communications (6) were made during the project, while a patent was submitted and obtained. The project also supported the creation of a network of French urban climate researchers which obtained support from CNRS (Social Sciences and Humanities) with seed funding for 2 years starting in 2025. The network includes 150 people from 50 laboratories as well as municipal and private sector members.

The UMat4CC project proposes an integrated interdisciplinary and systemic analysis of climate change adaptation in cities by focusing on the development of deployment strategies for cool materials and urban watering. In particular, it will develop methodological and technological tools for urban cooling in response to more frequent and intense heat-waves.
First, a geographical information system will be developed to assist cities in spatializing their urban cooling strategy. It will help rank urban areas according to their vulnerability to heat-waves, the exposure of their population and their cooling potential thanks to cool materials or urban watering. This work is based on an interdisciplinary collaboration between physicists and social scientists.
Second, experimental studies will be carried out in the laboratory on multilayer samples of three kinds of urban facets: pavements, façades and roofs. These experiments will study the fundamental thermo-climatic performance of cool urban materials as well as the performance of urban watering applied to these structures. Urban watering will also be optimized on the basis of these trials. Approximately ten samples of each type of urban facet will be studied under identical heat-wave conditions in a climate chamber with artificial sunlight in order to identify the dominant properties responsible for their cooling performance.
Based on this work, new material formulations will be proposed taking into account both new cooling objectives as well as existing mechanical (pavements) and thermal (facades and roofs) design goals. These results will be integrated into the geospatial analyses, in particular to assess the cooling potential of cool materials and urban watering.
Knowledge transfer to urban practitioners, decision makers and industry is at the heart of the project, which will draw on the expertise of a scientific and technical stakeholder committee and will disseminate the project's main results during an end-of-project seminar.