Green buildings

Image credit: Audrey Timm

Only choose hardy plants which are able to survive in rooftop conditions

Plants on extensive roof gardens should be able to survive and grow in high temperatures, full sun, high wind speeds and periods of drought. These should be able to survive in a thin substrate layer, a small waterbuffer and fluctuating temperatures.

The best plants for extensive roofs are:

• Perennial, low, seed-forming, drought tolerant plants
• Succulent plants with grey hairs or a thick blue layer on the leaves (sedum and sempervivum are available as plants or as ready-made living mats)
• Plants with strong woody twigs or thin leather like leaves
• Annuals that bloom and seed freely for continued presence.

A larger variety of plants can grow on an intensive roof garden

An intensive roof garden provides plants with more soil, water and fertiliser availability. Selection factors for plants include the height of the roof, wind speeds, irrigation availability, sun position, relation to other buildings, climate zone

The best plants for intensive roofs are:

• Plants that don’t get too big (maximum weight capacity), grow in full to half sun, can tolerate wind (do not use plants with lots of seeds that blow away, high plants with breakable or falling stems or plants with strong spreading roots)
• Perennials should be suitable for full sun and fully cover the ground
• Eco-roofs should consist of native or near-native plants
• Shrubs should be winter hardy, not be sensitive to wind, grow in full sun and grow in normal to dry soil, solitary shrubs can be pruned like trees. Low, drought tolerant shrubs are good choices
• Trees should only grow up to 6m high, not be sensitive to wind, have a crown that is not too big and open
• Trees with shallow roots must be anchored

Create green roofs on new and existing buildings and fulfil the need for green where space is limited in the urban environment.