2023-08-11 09:30:43
To deal with the problems of availability of water resources, the start-up Cactile has developed a system of modular tiles equipped with extra-flat reservoirs to store rainwater. It is suitable for sloping roofs as well as building facades. The co-founder of this company tells us regarding his innovation.
After working for 15 years in the hydroelectric production sector and developing a digital service to help manage water in rivers on the scale of watersheds, Jean-Baptiste Landes decided to take an interest in cities. Aware of the problems of availability of water resources, he notes that urban areas are home to a majority of the French population, but that these territories are very sealed, with few means to store water. He also observes that seen from the sky, the roofs of buildings can represent up to 50% of the surface of a city centre. He then imagined a system of light tiles equipped with reservoirs to store rainwater. After the development of several prototypes, it will soon equip several buildings. Interview with the co-founder of the start-up Cactile.
Engineering Techniques: What was your inspiration for designing your modular tile system?
Jean-Baptiste Landes, co-founder of the start-up Cactile. Credit: Cactile
Jean-Baptiste Landes: We took a lot of inspiration from the cactus, a plant species that has been able to adapt to extreme climatic conditions. Originally it was a tree, then its leaves became thorns, both to protect itself from predators, but also to cool itself and direct water drops to its roots. Its entire root system is close to the earth’s surface to collect water quickly before it evaporates and the largest cacti can store up to 4,000 liters in their trunks. This plant has also been able to change its behavior, since its photosynthesis takes place at night and no longer during the day, to avoid water loss linked to evaporation. Cactile, the name of our company, is the contraction of cactus and tile, which means tile in English.
How does your innovation work?
An illustration of low-profile rooftop tanks for storing rainwater on roofs. Credit: Cactile
Our system is divided into three functional layers. The first consists of large panels that measure approximately 1.5 m² and are fixed to the frame, in place of traditional tiles. They are currently made from recycled polypropylene, but we are testing other materials. Their role is both to seal the roof and serve as a receptacle for extra-flat water tanks. These reservoirs look like blocks of ice that are placed in a freezer, then kept cold in a cooler, and constitute the second layer. They are made of high density polyethylene (PE-HD) and are all interconnected with each other with the function of storing water.
The Cactile team is currently fine-tuning the design of the future cover elements of its system. Credit: Cactile
The third layer comes to cover the two previous ones and has the role of collecting rainwater and also has an aesthetic function, since it is the visible part of our system. Initially, we wanted to reproduce the shape of traditional tiles, and then by listening to architects, we decided to create our own design, in order to assume the singularity of our product. In the end, it is a metal roof, with a design halfway between a steel deck and a traditional tile.
What are the advantages of your system?
The final thickness of these three layers is between 6 and 11 cm thick and weighs less than 20 kg per m². Since the frames are designed to support 60 kg of tiles per m², the tanks can store up to 40 liters of water per m². Our device was designed in the opposite logic of conventional roofs whose role is to evacuate rainwater as quickly as possible, at the risk of seeing the collective water networks become clogged when torrents of water fall. Thanks to the shape of our tiles and their coatings, we manage to break the energy of the water to slow down its flow speed and make it fit as much as possible into the reservoirs. Using a digital simulator, we calculated that for a 60 m² roof, we can theoretically reduce water discharge into the stormwater network by 70% during a 30 mm storm lasting one hour.
We are developing a valve connected to a meteorological service to protect cities from flooding. In concrete terms, it will be able to automatically empty the reservoirs before an upcoming storm, to store as much water as possible when it occurs and thus prevent the collective network from overflowing.
Our tiles are eco-designed to reduce the impact of building roofing on the environment as much as possible. For example, we avoid mixing layers of materials, so that our system is easily recyclable at the end of its life.
How is the water recovered following being stored?
Since all the tanks are interconnected with each other, it is possible to lower the water to the desired place. For example, a toilet can be powered by gravity, without consuming energy. This indoor use is preferred, because there is no need for pressure and it is one of the main sources of water consumption in a home. Then, all authorized uses with rainwater are possible, such as irrigating plants or washing cars.
Who is your system for?
It is suitable for collective buildings equipped with large sloping roofs and mainly those managed by the State, communities, the public sector, social landlords. We are also aimed at all real estate players, such as architects, design offices, developers, etc. Our system is not suitable for flat roofs, however it can be fitted to facades, in order to create a useful cladding, like a second skin of the building. We also favor renovation, because it is one of the few products suitable for this. Our system was designed to avoid having to break everything in order to adapt cities to climate change as quickly and easily as possible.
In the first half of 2024, we will install a demonstrator at the Ecole des Mines d’Albi, where our company is incubated. The imagined structure will allow us to test our product on different roof inclinations as well as on facades. Then, we are going to equip five other buildings, including that of a school, a media library and two companies, private owners.
We benefit from the support of Ademe and we are going to take steps so that our modular tiles can be subsidized, in the same way as other rainwater recovery systems. We are continuing to develop our system so that it can also accommodate photovoltaic panels, which can also be subsidized.
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