The BâtiRoseau project aims to resolve the scientific bottlenecks behind the premature degradation of thatched roofs. The goal is to characterize the real hygrothermal behavior of these roofs in order to restore the industry’s technical confidence and structure the French reed production sector.

A material weakened by a lack of scientific knowledge

Thatch, whose use as a roofing material is part of France’s built heritage, is a local, bio-based material that is renewable every year. However, since the early 2000s, thatched roofs (Phragmites australis) have shown premature degradation, sometimes appearing as early as five to seven years after installation, which weakens the entire industry: insurance risk, recurring disputes, loss of confidence among project owners, and growing dependence on imports while French reed beds remain under-exploited.

These disorders remain poorly understood today: the involvement of the LIMBHA, our reseach laboratory, aims to resolve the scientific bottlenecks identified in BâtiRoseau’s preparatory work, in a context where the international literature on thatched roofs remains limited and fragmented.

Four objectives to rebuild the thatch industry

The BâtiRoseau project, led by Parc naturel régional de Brière, is structured around four main objectives:

1. Validate professional standards to facilitate the specification and insurability of thatched structures, by providing a recognized technical framework.
2. Better understand the material’s durability research work will aim to analyze degradation mechanisms — particularly fungal — in order to improve practices and extend the lifespan of thatched roofs.
3. Develop new uses for reed Beyond roofing, this involves exploring other applications for the material (processing into insulation panels, bricks, cob…) as part of a circular economy approach, and making use of reed-bed maintenance cuttings.
4. Structure the industry at the national level, by fostering coordination among the various stakeholders: reed bed managers (protected area managers such as the Conservatoire du littoral, Regional Nature Parks…), reed cutters, thatchers, architects, researchers, and training organizations.

LIMBHA’s scientific contribution

It is on the second objective, understanding the degradation mechanisms, that the LIMBHA focuses its work. It is working to characterize the real hygrothermal behavior of thatched roofs and to develop its modeling, by varying roof design parameters. A strong connection is maintained throughout the project with the University of Caen and UniLaSalle on the fungal aspects of degradation.

This characterization is expected to produce data series that are currently absent from the international literature — wetting kinetics, deep moisture progression, drying dynamics, hygrometric stratification — thereby providing the technical foundation needed to validate the professional standards targeted by the project’s first objective.

The project also includes a training component, with construction-focused projects and internships offered to our engineering students.