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A green roof (also known as a living roof, or a brown roof if designed to maximise biodiversity) is a growing system built on top of a protected waterproof roof.
The growing system can be grass, plants, small herbs, etc. Sedum is popular, planted with local wild flowers to provide variety.
They are useful for small animals and plants, adding greatly to biodiversity within the immediate local urban environment, and create extra green open spaces.
They also prevent flooding as water run-off is reduced and slowed down.
This is a big factor in urban areas as many gardens are concreted over, paved over for carports, or decked for play areas. Decking and tarmac greatly increase run-off rainwater.
Green roofs also help absorb carbon emissions - it all adds up.
They provide diverse habitats as they can be planted with indigenous flora for bird, insect and arthropod populations.
A green roof modifies the urban micro-climate. Plants through transpiration cool the air, and reduce surface roof temperatures by as much as 40 degrees centigrade in the summer, given the baking heat on a dark flat roof.
They also improve air quality, not only absorbing CO2 but also trapping about 85% of airborne particulates.
Roof gardens lose 30% less heat in winter and are cooler in summer, and also provide sound insulation.
A green roof can reduce indoor sound by as much as 10 decibels for every 3 inches of growth.
Green roofs have been shown to reduce heating costs by as much as 25% and cooling costs by as much 50%, for the floor directly under the roof.
The subsurface protects the roof against aging and replacement.
They also add value to a house or building.
They look very attractive compared to traditional grey slate or asphalt roofs, and provide a soothing effect for the stressed urban person.
The subsurface is a high tech system that holds water for dry periods. They can be very heavy, from 80 kg / square metre to 365 kg. This means most roofs will have to be structurally reinforced.
A recent study by US company Weston Solutions estimates that greening the rooftops of all buildings in the City of Chicago would result in nearly $100 million of annual energy savings.
Urban heat island effect can cause a 5 - 10 C temperature increase in large cities.
Types of Green, Living or Brown Roof
Pitched (slanted) green roofs and flat green roofs are built differently.
Flat green roofs are
Another design for a green roof is a biodiverse or brown roof. These are much the same as normal green roofs but are planted for maximum biodiversity or sometimes specific habitats for preferred types of flora and fauna, such as brown roofs where only local plants and animals are encouraged.
We have worked with Blackdown Horticultural UK.