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A - Indicative thicknesses for roof layers
Type Thickness* Dead load** Rainfall retention
Extensive 50 mm 0.7 kN/m² 50%+
Semi-extensive 200 mm 5 kN/m² 70%+
Intensive 600 mm 10 kN/m² n/a
* Overall thickness for growing medium and drainage layer
** Dead load based on fully saturated soil and drainage layer
B - Indicative costs of green roof
Sedum blanket only£35–40/³¾Â²
Sedum blanket with drainage layer and filter fleece£45–65/³¾Â²
Sedum blanket on filter fleece and drainage layers, capping layer and vapour barrier£80-115/³¾Â²
Extra for insulation£50/³¾Â²
Extra for waterproof membrane and vapour barrier£30-45/³¾Â²
250 mm thick growing medium on drainage board, root membranes and insulation; turf£85–100/³¾Â²
225 mm thick growing medium on filter fleece and LDPE drainage core; plug and hydroseed planting£50–60/³¾Â²