Green roof on garage

I have almost completed a garage, and today I put on a green roof supplied by Sky Gardens in the UK. The Verdant Blanket consists of 80 species of native provenance, chosen for suitability to green roof applications. I have bees (note the Warre bait hive full of bees in the background) which swung me to the flowers even though I know a green roof will not supply them much ... if anything. Also I'm going to be able to see taller flowers on the garage than a low,  sedum type planting. The cost of the blanket, substrate  (a light bark like and crushed brick mixture 80 mm), drainage layer, fleeces and river stone edging is about £42 m2. We installed in one day. (2.5 man days - my thanks to Des and David). It weighed in total about 2.5 metric tonnes or 100kg/m2. 

The second picture is the 'high tech' filter fleece and drainage layer.  The cups store water, and also provide a drainage path under the substrate.

The EPDM covered roof is designed for loads up to 200kg/m2, with a 200 mm up stand and 6 degree slope to a single drainage hole. Greater than 20 degrees and green roof design gets more complex. I suggest if building from new, just use ibeams and let your supplier do all the load calculations.

If I had done a simple turf roof I would have need 250mm of earth and would have needed a much higher design load.  While it may have been less 'technical' than this roof, it just would not have been practical for me. It often find green solutions require technology in my builds (like the drainage layer), which I try to resist as it somehow feels wrong, but often I have to give way to the practicalities or building regulations.