BSI PAS 100 compost as substrate component in green roofs

The results demonstrated that when combined with an appropriate mineral fraction, quality compost is a suitable and sustainable material that can support healthy vegetation growth in extensive green roof installations. The crushed brick mixes consistently gave the highest mean number of plants over time, and held more water than the other two minerals used.

A low level of organic matter is required for extensive green roof installations, in order to restrict plant growth and therefore reduce maintenance requirements. This was achieved in all substrate mixes where compost constituted 10 per cent of the substrate. Maintenance involved mowing two or three times during the first year, and once annually thereafter – no more than required to establish a wildflower meadow at ground level. However, irrigation of green roofs during the drier spring and early summer months may increase the number of species noted to be present, as well as broadleaf cover.