Rooftop gardens: creating a green roof or terrace

A garden on a roof or terrace is a way to get your own green corner in a city where there is no room for an ordinary garden. Green roofs insulate buildings, hold back rainwater and help cool the city. Here are the types of rooftop garden, what to consider before you start and which plants can cope with wind, sun and drought.

Plants for terraces and balconies are in our potted plants section.

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Types of green roof

• Extensive roof — a thin layer of substrate (roughly 6–15 cm) and undemanding plants, mainly sedums. Lightweight and almost maintenance-free.
• Intensive roof — a full garden with lawn, shrubs and even trees. It needs deep soil, a strong structure and regular care.
• Container garden — the simplest option for a balcony or terrace: plants in lightweight pots that can be moved around.

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Where to start

• Load capacity. Wet soil is very heavy — an engineer must calculate the load before the garden is built.
• Waterproofing and a root barrier — so water and roots don't damage the roof.
• Drainage — excess water must drain away or roots will rot.
• Wind and safety — secure pots and structures firmly and install railings.

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Suitable plants

• Sedums and houseleeks — the basis of extensive roofs, tolerant of drought and frost. More about the "stone rose" in "Stone rose (houseleek)".
• Ornamental grasses — fescue, miscanthus, fountain grass.
• Herbs — lavender, thyme, rosemary, sage.
• Dwarf conifers — mountain pine, juniper.
• For containers — petunias, pelargoniums, verbena and other annuals.

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Care

• Install drip irrigation: soil dries out faster on a roof.
• Remove weeds and tree seedlings blown in by the wind.
• Check the drainage and roof condition every spring.
• Feed container plants through the season.

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Inspiring examples

Among the best-known examples are the terraced green façade of the ACROS building in Fukuoka, Japan, and the rooftop garden on Chicago City Hall. Vertical greening is another way to add green to a city — see "Vertical gardens".

FAQ

Can a garden be made on any roof?

Only after an engineer has checked the load capacity and reliable waterproofing is in place.

Which plants suit a roof best?

Sedums, houseleeks, ornamental grasses, herbs and dwarf conifers.

What are the benefits of a green roof?

It insulates the building, holds back rainwater and reduces overheating in the city.

Author: Maria Svitlovir

Graduated from Taras Shevchenko National University of Kyiv, Institute of Biology and Medicine (2001). BSc in Biology, MSc in Horticulture. Writes about plants, works at a garden centre selecting and repotting plants, and contributes to plant reference guides.

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