A large-scale project, the new roof of an Auchan store near Bordeaux stands as an example of sustainable architecture and energy efficiency in an urban environment, primarily thanks to the use of white membranes that reflect the sun's rays.

Above the Auchan shopping center in Bordeaux, the light of southwestern France now shines brightly. The shopping center, whose original roofs dated back to 1995, was in dire need of renovation. The aging, original bituminous waterproofing no longer met thermal efficiency standards or the environmental requirements of a site frequented daily by thousands of visitors. The renovation project was therefore carried out with a clear objective: to make the building cooler and more energy-efficient. For Nhood, the technical manager of the Auchan group's assets, the lightness and energy performance of the future roof system were essential criteria. "Before, we had tar waterproofing, and now we wanted to switch to a lighter membrane. The second criterion was solar reflection. A white membrane has the advantage of not retaining heat," explains Romain Auffret, manager at Nhood.

White roof…

To meet these requirements, Cimalto, a Val-de-Marne-based company specializing in waterproofing, implemented the Renolit Alkorplan Bright membrane, a lightweight, reflective, and durable solution. The choice was made for several reasons: its installation without adding extra weight, its adaptability to the constraints of an occupied site, and above all, its energy performance. The membrane's particularly high solar reflectance index – exceeding 100% at certain wavelengths – significantly limits heat absorption. The result: a lower surface temperature and reduced air conditioning needs of 15% to 20%, without any modification to the HVAC system. Thermal images captured by drone confirmed this performance from the initial installation phases: the areas covered by the new solution showed a noticeable temperature drop compared to the remaining bituminous surfaces. The membrane's uniform whiteness is not merely a technical choice; it also contributes to the site's aesthetic appeal, visible from the surrounding roads. Its consistent finish provides seamless continuity with the visual appearance of the nearby commercial buildings. For Julien Pervalet, project manager at Cimalto, this project exceeded the client's initial expectations: "We went beyond what the client requested."

…and environmental awareness

Beyond the architectural gesture, the project is part of a broader initiative: the Cool3 campaign, led by the Renolit Group, which aims to combine technical innovation with climate commitment. Thanks to this program, every square meter of roofing installed contributes to reducing the overall carbon footprint. For example, for the 6,300 m² of roofing renovated in Bordeaux, 63 trees were planted via the Treedom platform, offsetting 21 tons of CO2. This initiative symbolizes the spirit of responsible innovation championed by Renolit Alkorplan Roofing Products, a subsidiary of the German group. For Cédric Salhi, Sales Manager for Southwest France, “this innovative project sets a new benchmark for roofing solutions while demonstrating Renolit’s commitment to innovation, environmental sustainability, and community. At a time when urban centers are constantly battling the effects of climate change, projects like this pave the way for the future by maintaining a balance between development and environmental responsibility.” The membrane installed here demonstrates that waterproofing is no longer just a matter of protection, but a key factor in energy efficiency and urban comfort.

Spotlight on pristine membranes

The Renolit Alkorplan Bright membrane is a high-performance reinforced PVC solution for flat roofs, combining durable waterproofing and thermal regulation. Its white surface with high solar reflectance limits heat absorption, reducing air conditioning system consumption by 15% to 20% and helping to combat urban heat islands. Lightweight and easy to handle, it is installed using hot air welding for watertight and discreet seams. Its tensile strength, dimensional stability, and durability against UV radiation and weathering make it a reliable choice for commercial and office roofs. Compatible with green roofs and photovoltaic systems, it offers lasting thermal comfort and aesthetic appeal to modern buildings.

Photo credits: Renolit

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