1. What are Living Roofs?

Living, or green, roofs are exactly as they sound; rooftops covered in vegetation. They are made up of layers of cultivating medium, drainage membranes, root barrier and waterproofing, all laid over a roof structure. Often, the original building may need additional strengthening to cope with loading from a 100 to 150mm build-up. Gently sloping roofs are commonly considered more suitable, as pitches steeper than 25 degrees are tricky to walk on and, when planted, prone to dry out more quickly, requiring extra irrigation. The lifespan of these roofs will depend on the quality of their substrates, but when correctly installed and well maintained could be between 30-50 years.

2. What are the basic maintenance requirements?

Upkeep demands depend upon the type of living roof and the chosen planting scheme.

Weeding and feeding a roof twice a year is recommended to ensure an even supply of nutrients and healthier, more robust growth.

There will often be an area of shingle around a roof's perimeter and a downpipe, or rain chains, to help with drainage.

Keeping roof edges tidy and gutters clear stops damage to the roof and the building beneath.

3. What types of living roofs are there?

'Extensive' living roofs are generally low maintenance and drought-tolerant, requiring little irrigation or maintenance. Self-seeding, these roofs often incorporate sedums (widely distributed fleshy-leaved plants with small star-shaped yellow, pink, or white flowers), grasses, mosses, and meadow flowers.

'Intensive' living roofs are far more complex in their formation and upkeep and are often actual roof gardens. They require a far higher load-bearing capacity and may include lawns, bushes, trees, terraces and even ponds.

'Simple intensive' living roofs usually comprise grasses, herbaceous plants and shrubs. Constructed using various depths of substrate (growing medium), they combine elements of extensive and intensive roofs.

Alongside the different types of living roof there are different approaches to planting. Growing and seeding the roof from scratch is generally considered the best method, allowing the plants to develop and adapt to their specific environment..

Pre-grown roofs are another attractive approach with blankets of sedum or wildflowers.

Also popular on living roofs are alpines, bulbs (crocus, dwarf iris, chives, cyclamen), native wildflowers, and native herbs (wild thyme, marjoram, basil).

4. What are the benefits of a living roof?

A living roof offers many practical advantages; they absorb heat from the sun, cooling a home down in the summer, whilst also soaking up CO2 and absorbing up to 70% of the water falling on them. They also add biodiversity, attracting wildlife and insects.

By lowering the temperature and reducing energy use, living roofs can help lower the concentration of air pollutants, improving air quality, climate and health.

In most cases, where living roofs are retrofitted on an existing building, planning permission is not required. However, it is advisable to discuss the implications of any kind of alteration to a building with the planning department prior to carrying out the works.

5. What is the history of living roofs?

The concept of a living roof stretches right back to the Hanging Gardens of Babylon, one of the Seven Wonders of the Ancient World. In 500 BC, Nebuchadnezzar II built the gardens for his wife, who was homesick for the plants of her native Persia.

The Vikings used green roofs, and they were also used in the Middle Ages as insulation. For hundreds of years, farmers in Scandinavia have been topping their houses with flora, stripping sod from surrounding grass meadows.

Historically green roofs were common in the UK, but they became less popular during the industrial revolution.

Presently, there is a resurgence in green roofs in many countries. London now has regulations requiring buildings of a specific size and function to have a green roof. Planted roofing has also grown significantly in popularity for residential properties.

Although there are no standards for living roofs in the UK, a partnership of industry and stakeholders came together to form the GRO, the Green Roof Organisation, to develop a recommended Code of Practice.