Innovative green roof for Lascaux IV

Greening system installed on roof with steep slope, using studs. Innovative system assessed by the CSTB. © Boegly + Grazia photographers / Snøhetta architects

The Centre International de l’Art Pariétal Lascaux IV (International Centre for Cave Art), which exhibits a reproduction of a prehistoric cave with paintings, was inaugurated in December 2016. Its green roof blends into the wooded landscape of the Dordogne region. The roof’s steep slope required an inventive design: 700 bollards hold the insulation material and vegetation in place over a roof of 7000 m2. Designed and installed by the company SNEI, which specializes in weatherproofing, this system received a Technical Experimentation Assessment (ATEx) from the CSTB.

Forest of bollards to secure the vegetation

The roof of the new Lascaux IV building slopes up to 45%, whereas traditional construction rules provide for a maximum slope of 15% for green roofs. To support the insulation material and protective plant cover, SNEI proposed a system of bollards integral with the structure and connected by crosspieces.

Sealing system assessed

Contacted by SNEI in July 2014, very early in the project, the CSTB used a preliminary supervision procedure and talked with the designers at the outset.

There was concern about the sizing of the 700 bollards and weatherproofing at their position points. One unusual design feature is the "inverted" weatherproofing in which the extruded polystyrene insulation panels are placed on top. The membrane is fully glued to the concrete support and rises up the sides of the bollards.

In addition, the multidisciplinary expert committee (construction, landscape and horticulture) convened by the CSTB attached great importance to the installation method and checks of the weatherproofing of the bollards, given their large number.

All the checks enabled SNEI to submit a complete technical file when it requested assessment. An ATEx was issued in March 2015.


Jean-Philippe Schillaci, manager, SNEI

« It was the first time we requested an ATEx. We absolutely had to win a favorable opinion because otherwise we would not be awarded the contract. A committee of eight experts reviewed the design we submitted. They focused on the bollard locations, checked our calculations and requested improvement of some safety factors. This assessment work reassured us about our design. It gives us confidence that the system can withstand the elements. The ATEx shows that we left nothing to chance. »

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