Water management for the roof of a Gironde secondary school

For the sports field located on the roof of this new school, the Rooftop Duo™ system developed in partnership with Lafarge Holcim allowed for a simplified architectural design and water management on the plot.

The challenge

The roof of the gymnasium of the new Emmanuel d'Alzon school, located in Saint-Médard-en-Jalles, was intended to accommodate a sports field. The architects absolutely wanted to retain the environmental approach they had developed for this project throughout the school, particularly with regard to the management and evacuation of rainwater.

In addition, the site presented several architectural challenges: an adjoining façade did not allow for the installation of water drainage and the surface of the ground had to be adapted for sports involving bouncing balls. The area also had to have the possibility to be used immediately after a downpour.

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Roof drainage systems

Roof drainage systems respond to the need to remove water from the flat surfaces and to possibly use it for another purpose. Such systems can be applied to flat roofs used as terraces with vegetable patches and gardens or for recreational and sporting purposes. Having decided whether the roof will be green or tiled, the core of the roofing system is comprised of a drainage layer, the purpose of which is to collect and recycle rainwater.

Water stagnation is, in fact, one of the most feared causes of water ingress in flat roofs. Water stagnation may be visible on the surface but also hidden underneath and occurs when the rainwater finds a layer that is not sufficiently permeable. In these cases, the accumulation of water can cause significant damage over time, leading in some cases to the need to carry out significant roof repairs.

Water ingress in walls, humidity, mould and condensation can in fact significantly damage the underlying building, thus extending the damage to the rest of the structure. Such situations are to be avoided as often the damage caused may not be visible for a long time. Damage to the roof is not always clear to see: sometimes the damage appears after a lot of storms and when the building installations have also been damaged.

It is, therefore, essential to pay close attention to the drainage system in order to avoid possible damage to the whole building in addition to the roof. The material laid over the drainage layer can play a key role in protecting against thermal shocks and solar radiation, as well as the wear and tear that its use will entail.

The solution

To meet the project management requirements, we proposed the use of our Rooftop Duo™ all-in-one solution. As a result of our partnership with Lafarge Holcim, Rooftop Duo™ combines their Hydromedia® draining concrete with our Wateroof honeycomb structure water retention system. Thanks to Rooftop Duo™, rainwater is drained directly through the concrete to the honeycomb structure, where it is temporarily retained, thus avoiding any water retention on the surface.

It is an effective solution to circumvent the challenges of draining rainwater from the site, while actively contributing to the environmental approach desired by the project manager. Thanks to Rooftop DuoTM, the architects were also able to simplify the structure of the roof by simplifying the installation of rainwater discharge, since our system allows a zero-slope roof, perfectly suited for a sports field. The reliability and architectural efficiency of our solution convinced not only the project management and project management; for the first ever, Rooftop Duo™ passed CSTB ATEx for this project. This evaluation based on project specifications, being the result of a demanding process, attests to the high reliability of the solution.

A draining flat roof as a basketball court for a school

Project Highlights

Project Highlights

  • Contracting authority: local authority

  • General contractor: Agence Dauphin, Architectes

  • Waterproofing company: Étanchéité du Sud-Ouest

  • Location: Emmanuel d'Alzon Secondary School, Saint-Médard-en-Jalles (33)

  • Period: July to August 2019

  • Products: Rooftop Duo ™

 A draining flat roof as a basketball court from the top

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