Green Roofs

If just a fraction of the flat roofs in our towns and cities became green roofs we’d have created a vast network of meadows in the sky. Imagine what that could do for birds, bumblebees and other pollinators!

What is it?

A green roof, also known as a living roof, is a roof area that has been built or modified to hold a specialist soil mix and drainage system that can sustain plants and other wildlife habitats. Green roofs can be heavy structures that require significant construction skills and materials. If you have the resources though, they can be a superbly valuable contribution to local wildlife.

Green roofs are relatively flat, less than 30 degrees slope, so the soil doesn’t slip downhill. They usually vary between 10cm and 20cm depth, the shallower types being more prone to heat, frost, wind and drying out, but nonetheless perfectly suitable for hardy plants like sedums and mosses. Deeper versions can host a wider variety of plant life and habitat generally but the considerable increase in weight makes them much more expensive.

What does it do?

Green roofs may be expensive, but they give back a huge amount to the community. They help reduce flooding by acting as sponges, soaking up and slowing water flow. They insulate the room below, providing cooling in summer and warmth in winter, and they also help cool the surrounding area by combatting the urban heat island effect.

Because they are fairly shallow and exposed to free-draining, low-nutrient soil, green roofs mimic the harsh conditions found in some of our most biodiverse meadows and grasslands. Hardier species, like sedums, provide valuable pollen and nectar even during hot, dry summer spells, and deeper soiled green roofs can play host to a huge diversity of flowering plants that provide a long flowering season for the roof as a whole.

Who benefits?

Pollinators like bumblebees, bee-flies, butterflies and moths will thrive on the pollen and nectar provided by sedums, bulbs and wildflowers growing on a green roof. They could be vital pitstops for any of these insects and more as they travel the neighbourhood in search of food, mates and nesting sites, especially on hot and dry days and when little else is flowering in the area. Seed-eating birds like finches will benefit from grasses and seed-bearing wildflowers, especially if they are left standing in winter. Bats, carnivorous birds like song-thrushes and insects like dragonflies may find them good hunting grounds.