Intensive green roof composition

Over the past decade, there has been an increase in the amount of green roofs being specified in the UK due to the huge environmental and economic benefits associated with them. Currently, green roofs are the fastest growing sector in the roofing market and in Northern Europe alone the sector has grown by approximately 35% over the past four years.

What is a green roof?
A green roof is the term for putting vegetation such as sedum, plants and trees on a roof, which also makes use of otherwise ‘dead’ space. There are three types of green roofs, which are Extensive,
Biodiverse (Brown) and Intensive. Extensive Green Roof Systems are designed to be virtually selfsustaining and they provide an aesthetic, low maintenance ecological feature, which can be admired from surrounding buildings. Due to a relatively shallow growing medium they are lightweight, making them ideal for use over most lightweight structuresand low sloping or pitched roofs.

Biodiverse (Brown) Roofs use recycled aggregate from brownfield sites, such as crushed brick and rubble, and are generally left to colonise naturally or they can be seeded with an annual wildflower mix or local seed source. The advantage of placing the existing brownfield materials on the roof, rather than sending it to a landfill site is that it will reduce the strain on the limited landfill space available and also eliminate any carbon emissions associated with transporting the material to landfill sites.

Intensive Green Roofs have a deeper growing medium than Extensive Green Roofs because trees, shrubs, turf and hard landscaping can be incorporated into the design. Also these systems normally require a complex irrigation system for maintenance. Due to the depth of the growing medium the holding structure requires adequate loading to withstand the associated weight of these systems.

Intensive Green Roofs are versatile, allowing the roof area to be utilised as highly aesthetic areas for recreation, public access or simply to be admired from surrounding buildings.

Reducing the Carbon Footprint
Many politicians, ecologists and companies are now looking at the term ‘carbon footprint’. The carbon footprint is a measure of how much carbon is being produced by a company or individual in one single action, such as importing or exporting materials via air, sea or road transportation and the production of electricity. According to the New Scientist, a study carried out by researchers at the Global Carbon Project found that carbon emissions grew four times faster between 2000 and 2005 than in the ten years preceding. The construction sector is responsible for nearly one third of all carbon emissions in the UK and if the UK government decides to penalise companies by taxing companies on their carbon footprint, this would have a huge affect on the industry.

Green roofs have been identified as an important component in reducing the level of carbon in the atmosphere. It is estimated that over a 30-year period, a 1,000m² of an Extensive Sedum Green Roof on a four-storey building would help reduce the carbon footprint or enable the building to become carbon neutral. This is achieved through the natural process of photosynthesis, whereby carbon dioxide is absorbed by vegetation and oxygen is released.

Extensive green roof composition

Economic and environmental benefits
Green roofs have many additional economical and environmental benefits, which include: reducing the Urban Heat Island Effect; improving rain water management; increasing the thermal performance of a building; reducing noise pollution and improving the aesthetics of the local area.

Urban Heat Island Effect (UHIE)
An Urban Heat Island is an urban area that is considerably warmer than surrounding areas. This effect is caused by various factors including: increasing heat, which is released from fuel combustion and humans, and also the configuration of streets, which do not allow radiation to escape because many of the roads, pavements and buildings are made from concrete and other such material that do not store heat. This initiates a change in the energy balance in an urban area, often causing it to reach higher temperatures.

By adopting a widespread green roof policy, the UHIE in cities could be reduced due to the vegetation on a green roof, which transfers less heat back into the atmosphere than a normal ‘grey’ roof. It is estimated that if green roofs covered half of all the buildings in New York, it would lead to a 1.0ºC reduction in surface temperature, dramatically reducing the Urban Heat Island Effect.

The UHIE also increases smog in cities because the polluted particles react on hot sunny days, making the smog more prominent. However, vegetation on green roofs is able to filter particles and absorb gaseous pollutants through photosynthesis, therefore, reducing atmospheric pollution.

Water Management
In recent years, flooding in towns and cities has become more common and one of the reasons for this is the UHIE. Moisture in the city condenses because of the increased temperature, which leads to the formation of rain clouds above the city, therefore, more rain is produced. In addition to this, in most UK cities there has been no investment made in the old fashioned Victorian sewers and some of these sewers are unable to cope with the volume of rain water being produced in today’s climate. A green roof can, therefore, aid water management by reducing the risk of flooding in towns and cities by reducing the amount of rain water run-off and also delaying the time at which run-off occurs. This results in decreased stress on Victorian sewer systems at peak flow periods.

Thermal Performance
The overall thermal performance of a building is dependent on, amongst other things, the thermal performance of the roof, walls, floors, windows and doors. Part L of the Building Regulations, which came in to force in April 2006, is designed to improve energy efficiency in new and existing buildings by increasing the amount of insulation required. A green roof can help to increase the thermal performance of a building by keeping the temperature within the building cooler in summer months, therefore, reducing air-conditioning costs. For example, a study by Nottingham Trent University found that with a mean daily temperature of 18.4°C, the temperature beneaththe membrane of a conventional roof is 32°C, whereas the temperature beneath the membrane of a green roof is only 17.1°C.

Noise Reduction
In 2005 the HSE’s Control of Noise at Work Regulations reduced the allowable level of exposure to noise in the workplace by 5dB to 80dB. Green roofs can also help to reduce the level of noise entering a building by 8db because soil blocks lower sound frequencies and vegetation blocks higher sound frequencies. This would be particularly beneficial to buildings positioned close to airports, motorways and busy train lines.

Improved Aesthetics and Health
According to a study carried out by Green Roofs for Healthy Cities, the additional vegetation provided by green roofs not only helps to visually enhance the concrete environment but can also aid the mental health of those living and working in cities. The variety of smells, colours and movements provided by plants can significantly add to people’s well being. Many urban hospitals have now been designed with this in mind, to help aid the recovery of patients, as they seem to respond well to having green areas within sight.

Liquid Plastics’ Green Roof Systems
Liquid Plastics’ has introduced a range of Green Roof Systems, which are unique because the company is the first in the industry to use the completely seamless, cold-applied Decothane Root Resistant Grade liquid waterproofing, which is a moisture triggered, aliphatic polyurethane. It is reinforced with glass fibre matting and once cured and buried, the system will perform for the design life of the building.

The company is also the first in the industry to achieve certification from the British Board of Agrément for a full Inverted Roof System (Certificate number 06/4359) and the Certificate states that Decothane waterproofing systems are suitable for use in “green roof specifications on flat roofs...”

The benefits of Liquid Plastics’ Green Roof Systems are that they are root resistant, highly durable and flexible, vapour permeable and all the products used in the systems are manufactured in the UK.
Liquid Plastics’ has partnered with Greenfix which will supply all the components above the waterproofing membrane. Together they are able to combine their expertise in both roof waterproofing and Green Roof Systems to provide a one stop service, giving the customer total peace of mind.

For more information on green and living roofs visit www.liquidplastics.co.uk or www.livingroofs.org

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