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Additional Resources

Read more about the CRITT Horticole Green Roof Research in the October 2009 Guest Feature on by Maxime Darnis and Philippe Faucon titled “A French Green Roof Research & Development Program”. For complete information, visit the ARRDHOR CRITT Horticole website.

The CRITT Horticole is a regional center of innovation and technology transfer specialized in horticulture approved by the French Ministry of Research and Universities. Our team of 10 engineers is located on the West Coast of France (oceanic climate), and works on several subjects related to the Horticulture Industry: greenhouse engineering, market analysis, plant death research activity and technology transfer to industrial, environmental and energy diagnostics for horticultural companies, horticultural activity support, and more recently: extensive green roofs.

We focused our research program on extensive vegetated rooftops with low maintenance because we think this is the most sustainable way to “green” buildings. Now, the main topics are:- Widen the range of species used on green roofs (plant diversification)- Understand and model green roof thermal behavior in order to quantify the benefits – Get references on commercialized systems (costs, environmental performance).

Here is a short description of our green roof research and development program, partially financed by the European Community (EC):

Plant Diversification – We are looking for physiologically and morphologically adapted species to withstand rooftops’ extreme environmental conditions. We try to identify some native species to improve the green roof relationship with the local environment, facilitate biodiversity development on the roof and also promote local identity. Moreover, a review of plant species associations is conducted to create new design patterns and more sustainable vegetation covers. The use of special plant communities with sustainable and self sufficient vegetation can reduce maintenance and resource input on green roofs. For instance, Fabaceae species, by fixing nitrogen, could enrich the soil locally and help other plants’ development.

A 200 square meter (2,153 sf) green roof platform was initially installed at CRITT Horticole, and we have recently extended the trials for a total area of 300 square meters (3,229 sf). It reproduces a double layer extensive green roof system with different substrate depths. Two hundred plant species have been tested here since 2009. Two hundred more species or cultivars are going to be planted.

Thermal Performance Studies – We are developing an energy balance model of a vegetated roof and integrating it in a building energy simulation program (TRNSYS) in partnership with the LEPTIAB (Universite de La Rochelle). At the same time, in order to understand precisely the phenomenon, we study and quantify thermal and mass fluxes. The roles of growing media, vegetation and drainage layer characteristics on thermal behavior are evaluated experimentally on a green roof modular platform. The experimental results will be usable for model validation.

The platform consists of 30 green roof modules (1 square meter or just under 11 sf each). These are made in stainless steel covered with root-proof membrane and filled with different green roof systems (single layer with 2-substrate depth, multilayer with different drainage layer types). Vegetation structure and density may also influence thermal efficiency of green roof. Therefore, two plant types were planted: grassy forms (Festuca glauca) and carpeting plants (Sedum acre and Sedum album). The green roof modules are in a greenhouse in order to control climatic conditions but will be transported outside for other experiments (see below for further research).


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