A few months ago we posted an update on the new green roof at CAT, made possible thanks to a donation from the People’s Postcode Trust. So far the roof has been rather more slate-grey than green. Today, however, the planting of the roof began!
We chose to colonise the roof with sedums – hardy alpine succulents – that are also known as stonecrops due to their ability to adapt to extreme growing mediums. Up at CAT we have sedums growing naturally in the disused quarry on slate waste.
The plants chosen for the roof, however, came from the walls and roof of Jony’s – CAT’s Artist in Residence – house. They are, he explains, “a completely homegrown tray of sedum from mid-Wales […] We’re pit planting these in organic potting compost. The roof is like a scree slope of shale that’s falling down the mountain. The plants root themselves in this medium, and the slate also acts like a mulch to stop weeds growing. You need something completely inert that weeds won’t grow in.”
Over the next few years these small plants will slowly grow and spread across the roof until they cover it entirely.
A Green Roof (or Living Roof) is like a shallow box garden. The bottom and sides are lined with a waterproof covering, then with a special membrane with small pockets to collect water to allow for slower drainage. A growing medium (in this case slate chipping) is laid down and then the sedums are planted.
Green Roofs are an important example of the kind of technology that can help us adapt to climate change. They help reduce surface water flooding in cities by absorbing storm water quickly, but releasing it slowly. They also help reduce hotspots of overheating in cities, provide important habitats for biodiversity in urban areas and offer potential spaces to be used for growing food. In general, they don’t give much in the way of insulation, so a roof still needs to be properly insulated.
Although Green Roofs are not a modern invention, it is the recent advances in water-proofing technologies that have led to Green Roofs becoming more widely used in sustainable construction over the last decade.