Type of works: supply and installation of a modular green roof.

This project was carried out in early March 2009, on an existing inverted flat roof with restricted access.

The roofing contractors were carrying out the work themselves and were keen to get a fast, relatively simple solution.

Wallbarn recommended sedum because of the lack of access to water, and to maintain the area. It recommended the modular tray option as the contractors were not experienced installers of green roofs, and wanted to ensure proper substrate levels were achieved and the vegetation was not damaged during installation.

Insulation was placed onto the asphalt roof and a layer of geotextile fabric was laid on top, to act as a separation and filtration layer and aiding in the direction of the water run-off.

The modular green roof trays were delivered wrapped onto pallets. Although the modules were stacked, they could survive for up to 2 days in this state as an air-gap was present between the cups of the drainage sheeting. However, immediate installation is recommended as the plants depend on light and will not survive for over 48 hours after stacking.

The modules could be craned onto the roof, and installed by two people by simply laying one tray next to the other, and clicking one row of cups from one tray into a row of cups on the neighbouring tray. The substrate and vegetation could be gently folded back to give more access to the installers, and once each module was secure; the sedum could be gently and carefully patted into place.

Care was needed to ensure none of the substrate or root system was damaged during this process.

The sedum and drainage systems could be easily cut around pipework and other details, and a row of washed pebbles was then placed around the perimeter of the roof.

The 65m² roof was completed in one day, and the roofing contractors were very pleased to have been able to invoice the client for the complete works, rather than having to sub-contract to special installers.

The sedum was installed when still in its winter state, and has now grown considerably with the help of a liquid fertilizer, provided by Wallbarn. The area is now lush and green, with almost complete coverage.