Greening warehouse roofs: the benefits of green roofs
Logistics warehouses are continuing their shift toward stronger environmental performance by greening their roofs. Green roofs offer an appealing alternative to photovoltaic systems, particularly in urban and suburban areas.
Since 2019, the Energy and Climate Act has required the greening of roofs on new warehouses with a ground footprint of more than 1,000 sq. m. Through the Climate and Resilience Act, lawmakers will lower this threshold to 500 m² as of January 1, 2023. This greening can be achieved either through renewable-energy production systems, green roofs, or “any other system” delivering a similar result—such as reflective resin coatings on warehouse roofs to improve thermal comfort.
The signatories to the mutual-commitment charter on the economic and environmental performance of logistics real estate are well aware of these requirements and have even undertaken to step up their efforts beyond the initial regulatory constraints. What are the benefits of green roofs? In which cases is it appropriate to prioritize biodiversity over the kilowatt-hours generated by a photovoltaic roof? Some answers.
An alternative to solar roofing for greening warehouse roofs
“Making roofs functional is a major issue. First and foremost, they must provide effective waterproofing and insulation. Now, we need to go further and add value to these square meters of roof space,” explains Michel Schmitt, Director of Sopranature by Soprema. This is Soprema’s division offering green-roof solutions for building flat roofs. “It is an evolving market, with growth estimated at around 10% per year,” but it faces competition from photovoltaic roofing. “With a solar project, the warehouse owner receives revenue from electricity sales, which amounts to a form of rent and therefore a return on investment,” Michel Schmitt acknowledges. “Green-roof solutions, on the other hand, make it possible to introduce biodiversity on the warehouse roof, which can sometimes be made accessible to building users as a place to relax,” thereby increasing user comfort.
There are two types of green flat roof, depending on the roof’s thickness. “For extensive or semi-intensive roofs of medium thickness, we are constrained by load-bearing capacity and mainly install sedum mats (a plant known for its resilience, Ed.) which we can supplement with perennials for greater diversity, explains the Director of Sopranature by Soprema. For stronger roofs, we can offer bespoke solutions with richer green-roof systems, for example to align with local plant species.”
Green roofs: a practical solution in urban areas
Above all, a green warehouse flat roof helps address planning constraints, such as stormwater runoff reduction. “In urban areas, the local zoning plan sets a maximum water flow rate to limit the risk of overloading wastewater networks and, consequently, flooding. A green warehouse roof is an excellent solution in the city.”
Both visually appealing and useful in cities, green roofs are also popular with users. Daniel Pais, Director of Logistics Programs at Quartus Logistique, explains the expectations of certain clients: “First, they improve the buildings’ landscape integration, while also making it possible to meet green-space requirements on sites that are almost entirely built up.” Greening roofs also provides a regulatory response to clients’ specifications, with several projects currently being developed by Quartus teams: “In Lyon, we are developing HLU—Hôtel et Logistique Urbaine—at the tip of the Perrache peninsula. In urban areas, conventional steel-deck roofs can be seen from neighboring buildings or public spaces; that is why we are greening part of them. We have projects underway in several French metropolitan areas, where we are developing solutions that combine photovoltaics and green roofs.”
Essential to everyday needs, urban logistics must address a wide range of challenges. Quartus Logistique’s expertise is decisive in this respect, through a planning tool made available to cities to optimize their logistics operations, boost their attractiveness, help improve their environmental footprint, and enhance residents’ quality of life.
Not every warehouse is necessarily suited to roof greening, Daniel Pais confirms: “While in urban areas a green roof plays a leading technical and visual role, in rural areas there is often sufficient space to build stormwater retention basins. In addition, roofs can reach heights of around 15 meters, where green roofs cannot benefit employees or local residents.” While Michel Schmitt and Daniel Pais agree that green warehouse roofs are set for strong growth in the coming years, especially with the forthcoming goal of “no net land take,” the Quartus Logistique developer notes that insurance risk management can dampen enthusiasm: “An incentive-based approach is needed to provide reassurance about issues relating to allowable loads and warehouse waterproofing.” He concludes on this solution’s bright future: “By continuing to improve the quality of planting in roof-greening projects, we help improve quality of life in cities.”
The implementation of green roofs, validated by recent studies (such as that of the Île-de-France Regional Biodiversity Agency), facilitates the integration of logistics platforms into their local areas and helps combat climate change. The development of new complementary measures to achieve the law’s targets for greening warehouse roofs could further strengthen these benefits in the years ahead.
