A green roof can aid the thermal performance of a building

Before 1995, green roofs were virtually non-existent in the UK, now just over 12 years later there are approximately 35,000m² of green roofs in London alone and another 600,000m² are planned by 2017.

And with large numbers of new schools being constructed as part of the Building Schools for the Future initiative, many are looking to enhance their ecological characteristics with the addition of a green roof system.

One of two Ilford extended schools planned for construction during 2007; Winston Way incorporates sustainable features in its design whilst serving the surrounding community, and has an anticipated total number of 630 pupils plus nursery. As part of its innovative design the school required a series of different types of roofs, including four green roofs and a fully insulated Cold Fusion Bonded Built-up roofing system.

There are many economic and ecological advantages of having a green roof including reducing the carbon footprint, improving the air quality, reducing the Urban Heat Island Effect and increasing the thermal performance of a building. Vegetation has been identified as an important component in reducing carbon emissions, and it is estimated that over a 30-year period a 1,000m2 of extensive sedum green roof on a four-storey building can help the building become carbon neutral.

The Urban Heat Island Effect occurs when an urban area is considerably warmer than the temperature in the surrounding areas. By adopting a widespread green roof policy, the Urban Heat Island Effect in cities will be reduced because the vegetation transfers less heat back into the atmosphere than the normal grey roof surfaces, which exasperate the Urban Heat Island Effect.

If green roofs covered half of all the buildings in New York, this would lead to a 1ºC reduction in surface temperature.

A green roof can also aid the thermal performance of a building. In the summer months, the green roofs help keep the temperature in the building cooler, therefore, reducing air-conditioning costs. Whilst in winter, green roofs act as further insulation, this means that the building is kept warmer and heating costs are reduced. In addition the layers of protection in a Green Roof System will reduce noise by 5dB or more, as soil blocks the lower sound frequencies and vegetation blocks the higher sound frequencies.

Extensive green roofs are a suitable solution for providing an aesthetic, low maintenance, ecological feature, whilst intensive green roofs are versatile, allowing the roof area to be utilised as a highly aesthetic area for recreation, public access or simply to be admired from surrounding buildings. Liquid Plastics’ green roof systems are unique because they are the first cold applied, moisture triggered, polyurethane systems to be used for a green roof.

Completed inverted roof system

Other benefits include the highly elastomeric, vapour permeable Decothane membrane that is guaranteed to last for at least 25 years, and has been successfully tested to DIN 4062 5.7 Root Resistance Test standards to conclusively prove that it cannot be penetrated by the roots of plants when used as part of a Green Roof System.

Winston Way School has one intensive green roof system installed, which provides a fully accessible educational area for the children, allowing them to learn about different plant and flower species in their own eco-garden.

The remaining green roofs received an extensive green roof system, simply completed with a sedum mat requiring minimal maintenance and providing an aesthetically pleasing and environmentally-friendly finish.

In addition to sourcing environmentally friendly solutions, many construction sites also aim to avoid the use of hot works on the roof. “We sought a supplier that could not only provide quality solutions for each of the different roofs, but could also guarantee the work and eliminate the need for hot works,” comments Charles Parnell, Architect for London Borough of Redbridge. With its completely cold applied waterproof roof membrane – Decothane – Liquid Plastics was able to supply waterproofing solutions for all of the roofs, including four green roof systems, five fully insulated built-up systems, and a cold applied and seamless inverted roof.

The seamless nature of Decothane also allowed the deck to be cast flat in places, and the liquid application meant that penetrations could be quickly and easily waterproofed.

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