Sustainability: Green roofs | Features

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/m²
Sedum blanket with drainage layer and filter fleece	£45–65/m²
Sedum blanket on filter fleece and drainage layers, capping layer and vapour barrier	£80-115/m²
Extra for insulation	£50/m²
Extra for waterproof membrane and vapour barrier	£30-45/m²
250 mm thick growing medium on drainage board, root membranes and insulation; turf	£85–100/m²
225 mm thick growing medium on filter fleece and LDPE drainage core; plug and hydroseed planting	£50–60/m²