1. What is a green roof?
2. Permaroof UK LTD and Green Roofs
3. The History of Green Roofs
4. Types & Terminology – Extensive
5. Types & Terminology – Intensive
6. Types & Terminology – Brown
7. Types & Terminology cont.
8. Components
9. Extensive Green Roof Drainage – Permaroof Roofdrain
10. SUDS and Rainwater Attenuation
11. Intensive Green Roof Drainage – Permaroof Deckdrain
12. Benefits of Green Roofs
13. Barriers & Myths
14. Design Considerations
15. The Future
16. Summary

1. What is a green roof?

“ A Green Roof is an intentionally Vegetated Roof “

Sounds simple and in essence it is, provided you seek expert guidance along the way. Finding the right company to assist you at each stage of the process is the difference between the success and failure of the project.

This website is designed to be a simple introduction to Green Roofs and will hopefully be of great use as a point of reference.

For project specific advice please contact our experienced and knowledgeable team direct on 0800 161 3722 or greenroof@permaroof.co.uk

2. Permaroof UK LTD and Green Roofs

Permaroof UK Ltd are a UK based Importer and Distributor of specialist single ply materials, alongside an extensive range of geocomposite drainage products, geotextiles, geomembranes and several specialists SUDS related systems. We also supply composite soils and wide variety of plants to complete a wide variation of green roof solutions. Together it makes the Permaroof Green Roof System.

We first became involved in Green Roof projects approximately 2 years ago when developing and launching our own range of products specifically with Green Roofs in mind. Since this time we have supplied products to projects throughout the UK & Ireland. Products supplied include 1000’s m2 of geocomposite drainage, composite soils and sedum/wildflower for both extensive & intensive Green Roofing projects.

Over the years we have developed a number of long term relationships with fellow suppliers and installers which in turn have enabled us to offer a complete Permaroof Green Roof package specifically tailored to the needs of the client.

Permaroof UK are working to develop a UK specific Green Roof which is tailored to the geographical location and climate conditions of the UK. We have established development partnerships with a major producer of drainage systems and a portfolio of specifiers and construction companies. We will continue to investigate and develop the environmental benefits of Green Roofs and provide guidelines and training on the best practice. We will also develop a UK system with native plants to encourage local biodiversity with focus on sustainable drainage systems. These will consider the hydrology and maximize the attenuation of water to encourage plant survival and growth whiles alleviating storm water run off.

3. The History of Green Roofs

When hearing the term ‘Green Roof’ people quite often assume that this is a relatively new concept aimed at helping the counter effects of climate change. You may be surprised to know that the concept of Green Roofs date back as far as the 6^th century BC.

More recently, the 20^th century saw an increase in the number of flat roof areas. This was partly due to the utilization of concrete in buildings. The knock-on effect was an increase in the number of terraced roof gardens.

The 1950’s saw the first real period of the development in the Green Roof technology. This development continued throughout the 60’s and 70’s, meaning that by the 1980’s and technical difficulties had been overcome and the Green Roof as we know it was born.

As our counterparts in mainland Europe and America have continued to increase the number of Green Roofs through legislation and incentives, the UK has fallen behind. This is beginning to change.

A combination of progressive urbanization and climate change, resulting in more intense rainfall has increased the volume of rapid run off from hard surfaces. This has been highlighted by the recent flooding which devastated the South Yorkshire and Humberside areas in 2007. Green Roofs have important role in mitigating these effects by forming a sustainable drainage system (SUDS)

4. Types & Terminology – Extensive

You are no doubt aware that there are various types of Green Roofs and a number of terms commonly used to describe them. But what do they actually mean?

Characteristics

Extensive Green Roofs are probably the most common type of Green Roof. An extensive roof consists of a shallow layer of substrate, typically 20mm to 200mm deep and a variety of drought tolerant hardy plants/vegetation.

Also preferred to as a turf roof or sedum roof.

Maintenance

Extensive roofs are relatively self sufficient and are not designed and constructed with the intention of being trafficked by pedestrians. Therefore access to the roof tends to be limited other than the occasional maintenance. Vegetation should be selected with this in mind.

5. Types & Terminology – Intensive

Unlike extensive Green Roofs an intensive Green Roof can be as simplistic or as complex as the client desires.

Characteristics

Intensive roofs consist of deep soil layer; typically 150mm to 1500mm. Due to this soil layer there is greater scope when it comes to planting. The roof can be viewed very much like a traditional garden area and within reason can be landscaped accordingly to include tress, lawns, flower beds and paved areas.

Also referred top as a roof garden or living roof.

Maintenance

Generally speaking when it comes to maintenance and intensive Green Roof requires the same level of care and attention as any traditional garden.

6. Types & Terminology – Brown

The term Brown Roof is commonly used to refer to a roof where the vegetation is intended to replicate the existing Brownfield habitat.

With an increasing number of developments Brown Roofs can partly mitigate this loss of habitat.

Characteristics

This type of roof can be seeded like the intensive or extensive roofs or self colonized. Please that seeding does increase the bio diversity potential of the roof in the short term.

Also referred to as a biodiverse or rubble roof.

Maintenance

Similar to that of an extensive Green Roof. Minimal maintenance is required. Aggregate & vegetation choice is determined by the biodiversity objective the client would like to achieve.

7. Types & Terminology cont.

Semi intensive/amenity

There are many projects where the Green Roof does not fit neatly into either an extensive or intensive category. These include some of the characteristics of each type and are termed semi intensive or amenity roofs, as they are usually intended for recreational purposes.

The roof can include hard and soft landscaping which can have a variable depth and type of substrate. Trees and shrubs that require deeper soil can be accommodated in planted or raised beds.

An amenity roof often includes water management by means of SUDS, attenuation, drainage layers, rainwater harvesting and irrigation.

This can and should be designed with the geographic location and attenuation requirements to complement the UK’s environmental needs.

Podium Decks

Many modern developments incorporate landscaped roofs, at terrestrial level, for example above basement areas and shopping precincts. These areas are commonly referred to as podium decks.

The deck areas themselves help create additional usable space in populous towns and cities, as car parks or recreational parks. Whether the intention is to create a hard or soft landscaped area it is important to consider the design implications of the deck. Key considerations include: protection of the waterproofing, drainage, water retention, outlets and design loads

For large areas such as car parks or recreational spaces it is imperative that the consideration is given to provision of adequate subsurface drainage below the topsoil layer and paving. In many cases geocomposite drainage layer provides subsurface drainage and protection to the waterproofing.

8. Components

Waterproofing & Insulation

Selecting an appropriated waterproofing and insulation system is achieved on a project specific basis. For reference virtually any type or roof structure and waterproofing is suitable to have a Green Roof, including new build and retro-fit. Please contact Permaroof UK direct for further assistance.

The U Values of Green Roofs are, at the moment, under detailed study and comprehensive tests have not yet been established. Green Roofs are proven to have a cooling effect in summer and we are currently working to determine whether they assist the insulation against heat loss in winter. Until the findings are published Green Roofs still rely on the usual insulating layer to meet specification.

Plants/Vegetation

Plants are selected on a project specific basis. Plant choice should reflect on sir pollution, location, building, height, shade, weight limitations, level of maintenance etc… the choice is also dependent upon what the client wants to achieve i.e. does it need to be green from day one?

For intensive roofs there are 4 main options when it comes to vegetation and planting:

Pre Grown Mat – a vegetation mat where the material is grown to maturity rolled up and supplied in the form of a mat. This can be either sedum, turf or meadow plants to create an instant effect.

Plug Planting – ideal for smaller projects. This involves planting species such as sedum, typically 20 per square meter. For a fuller cover you van incorporate cuttings or simply increase the number of individual sedums per square meter.

Brown roof vegetation – replicating the existing site conditions on the roof.

Hydro seeding – the process of spraying specially mixed slurry comprising of water, seed, mulch and fertilizer directly on to the substrate. It typically takes 12 – 18 months for full coverage.

Substrate

The substrate used in green roof projects can be designed specifically to suit each project and this can be varied to meet the requirements of the vegetation and surrounding ecosystem.

The substrate can range from low nutrient site specific medium such as a limestone mix for calcareous grasses and plants, to a composted nutrient mix to support geophytes such as snow drops or daffodils and a range of herbacious plants and other native perennials.

The most common mix for extensive Green Roofs is a free draining formulated layer consisting of organic, inorganic, mineral and recycled components, sometimes sintered clay or slate is added to aid the absorption of rainwater, the material is lightweight and helps minimize weight on the roof structure.

The most common mix of intensive Green Roofs uses a denser and slower draining substrate. This consists of both organic and synthetic materials to stimulate a topsoil type material which can support a wider variety of vegetation.

Edging Detail

Whilst Green Roofs are accepted as fire resistant, additional fire prevention methods, such as firebreak, should be taken in consideration at the design stage. The need becomes more prevalent in the case of extensive roofs, primarily due to their shallow layer of substrate and general lack or irrigation.

A typical firebreak would consist of a 300mm wide layer of 20 – 40mm rounded stone or decorative gravel. This layer should be equal to the depth of the build up and run parallel with the perimeter of the roof.

9. Extensive Green Roof Drainage – Permaroof Roofdrain

Drainage and water storage are particularly important components in any Green Roof project. As a major green roof supplier we have sourced the most effective drainage and filter products to suit both intensive and extensive roofs.

Extensive Green Roofs consist of a thin substrate growing layer. During dry spells this substrate would dry out quickly, impacting upon the plants themselves.

Permaroof Roofdrain is a lightweight water storage geocomposite primarily intended to solve this problem. In addition to providing drainage the perforated Roofdrain Core provides a water reservoir for plant roots, storing between 4 and 20 liters per m2 and in turn aiding sustained growth during dry spells.

Permaroof Roofdrain attenuates the rainfall run off and is therefore and active SUDS system. This ability to control the discharge rate is a key criteria in overcoming planning constraints.

10. SUDS and Rainwater Attenuation

As much as 95% of rainfall on undeveloped land is naturally absorbed into the vegetated surface only 5% becomes a run off. Within a catchment area the streams and rivers have evolved in response to this minimal discharge from the land. Urbanization and development of land creates hard impervious surfaces that absorb only 5% of the rainfall, a huge 95% of the rainfall becomes run off. The streams and rivers cannot accommodate this huge influx and the result is severe flooding and erosion.

The only viable solution both economically and ecologically, is to ensure that the built environment has a similar rainfall response to the natural land. One method is to build SUDS tanks below ground to store excess water until the rainfall has abated. The other method is to construct Green Roofs so that building directly replicates the land on which it is built and discharge is reduced to less than 5% as run off.

A Green Roof is the natural way to attenuate rainfall. It can also be, in certain situations, the most economical method. In addition a Green Roof will function in areas where a SUDS tank will perform poorly e.g. clay, contaminated land, aquifers etc….

For Green Roof to provide a SUDS solution the geocomposite, water attenuation and substrate layers are specifically designed with enhanced water storage capacity. Storage capacities approaching 100 liters per m2 can be achieved this way. This stored water can be released slowly or used as grey water or irrigation for the vegetation.

A Green Roof provides ecological benefits to the local flora and fauna that a SUDS tank cannot.

11. Intensive Green Roof Drainage – Permaroof Deckdrain

As intensive Green Roofs have a far greater depth of soil this layer is less likely to dry out but requires good drainage to ensure that the roof does not become water logged.

In this instance we offer Permaroof Deckdrain. The product consists of a combination of either a 12 or 25mm think cupsated core with a geotextile fleece bonded to the upper face.

Permaroof Deckdrain provides excellent drainage over the whole base area of the soil layer in addition to providing additional waterproofing protection.

Please note: both Deckdrain & Roofdrain incorporate a filter fleece and can be rolled out during installation as an all in one layer.

The DECKDRAIN product is also environmentally friendly and can be made of 95% recycled material, thereby helping reduce the carbon footprint.

Also, we offer a range of different roll sizes and widths which reduces waste and makes the product very cost effective.

12. Benefits of Green Roofs

Stormwater Management

Green Roof design works be retaining water, in some cases as much as 90% thereby significantly reducing storm water run off and playing and important role in reducing the risk of flash flooding.

Added protection for the waterproofing layer.

The build up above the waterproofing membrane is proven to greatly increase its life expectancy. The build up helps reduce the impact of temperature fluctuations, thereby reducing thermal stress. Several waterproofing companies have realized that a Green Roof actually protects the waterproofing from thermal differences in temperature and in turn, stops expansion and contraction whilst also protecting the waterproofing from UV rays. This prolongs the life of the waterproofing and many partner waterproofing companies have extended their warranties when a Permaroof Green Roof is installed.

Extracts pollutants

The vegetation & soil filter dust and pollution from the air and rainfall thus reducing the amount of chemicals and pollutants that reach the river networks.

Aid planning consent

Although there are no regulations in the place regards to Green Roofs, many local authorities favor proposals that incorporate sustainable drainage systems.

Mitigating the Urban Heat Island effect

City centres are known to have higher temperatures than surrounding the rural areas. This is due to a number of factors, many of which are linked to the specific heat and impervious nature of city surfaces such as concrete, tarmac and traditional membrane roofs. This is known as Urban Heat Island Effect.

Other advantages

Green Roofs help create a living habitat for small wildlife & a wide variety of plant species; create more accessible space in densely populated areas; more aesthetically pleasing than a traditional roof.

Noise reduction

A Green Roof is also very good at reducing low frequency sounds, an extensive Green Roof can insulate up to 40dB and an intensive Green Roof can insulate up to 50dB which can make a noticeable difference especially near airports.

Reduced air conditioning load

Green Roofs cool in summer thus reducing the energy consumption of the building and decreasing carbon emissions. This helps to reduce the urban heat island effect.

A study in Toronto estimated that direct energy savings through city wide greening would result in a reduction in peak demand and result in saving of approximately 55,000 metric tones of fossil fuels per year.

BREEAM

By improving the energy performance of building and embracing Green Roofs not only does it help to meet standards such as the code for sustainable homes and BREEAM, it also helps to meet planning requirements and the revisions to Part L Building Regulations. A development which incorporates a Green Roof can earn up to 6.2 points on an eco homes score. A green Roof also contributes to sustainability and enhances local biodiversity. This provides a solution to environmental policy issues which saves the developer time and money.

13. Barriers & Myths

“Green Roofs are expensive to maintain”

Even though extensive Green Roofs are relatively self sustaining, they still require some form of maintenance. Permaroof UK recommend this should be dealt with in the form of a maintenance contract. Maintenance for extensive roofs will typically be require twice in the first 12 months, then once annually thereafter. Therefore the overall cost of maintaining a Green Roof can relatively minimal.

“Green Roofs cost more”

In terms of initial outlay Green Roofs are generally more expensive than conventional roofs. However when taking into account factors such as the whole life cost of the building, the reduction in other infrastructure such as Stormwater tanks, and the extension in the life of waterproofing membranes this is additional cost can be easily offset. In fact, extensive Green Roofs provide a positive cost benefit.

Until UK legislation arrives, cost will inevitably be a determining factor as to whether the Green Roof project goes ahead or it doesn’t. At Permaroof UK we work with a varied network of specialist suppliers enabling us to provide each component of the Green Roof. As opposed to having a ‘one system fits all’ approach, our supply chain enables us to put forward bespoke systems to meet the needs of the client, on time and within budget.

“Green Roofs are susceptible to fire”

A fire is actually 20% more likely to occur on a bitumen exposed roof. In addition to this sedums used on most extensive green roofs are succulents which do not burn easily. Another important element is to include for shingle fire breaks around the perimeter of the roof.

“A Green Roof will leak”

On the contrary, a Green Roof will actually help protect the membrane from the weather, whilst the root barrier will prevent any damage to the waterproofing caused by plant intrusion.

Please ensure the waterproofing is leak tested prior to installation of the green components. Contact Permaroof UK for advice prior to installation.

14. Design Considerations

There are a number of important considerations when planning and designing a Green Roof.

Structural Loadings

The introduction of a Green Roof will have loading implications for the building. It is vital to consult a structural engineer at any early stage. This will enable you to determine any constraints you may be under and in turn help decide which type of Green Roof system to implement.

Example

Saturated

Type Weight (kg/m2)

Extensive 60 – 150

Intensive 200 – 500

Compressive strength

A factor which is commonly misinterpreted is the structural requirements for the drainage layer and erroneous descriptions such as 1000 kPa are sometimes mentioned.

This is significantly greater than the requirements of the roof and indeed most roofs do not need anything over 150kPa. The diagram to the right, which is from independent test data, shows the pressure exerted by a fully loaded construction vehicle. As you can see the loads exerted by vehicles on Green Roofs and podium decks are actually quite low.

The chart shows the compressive strength of a 500kPa HDPE geocomposite drainage product and in particular that a product designated as 500kPa working load, actually has a peak compressive strength of 1200kPa. This means that a 500kPa product can accommodate high short term construction loads and will also provide long term performance under design loads without danger of collapse.

Access & Maintenance

Even extensive roofs need occasional maintenance. Provisions must be made for this. The BRITISH STANDARDS INSTITUTION state that all new builds must provide access to the roof area to enable a minimum of 2 inspections per year. The installation of a green roof does not change this, but if there no edge protection on the building, health and safety regulations require anyone within 2m of the edge to wear a safety harness.

Drainage & Water retention

Drainage and water retention are key elements to consider when designing a Green Roof. The specific type is entirely dependent upon the proposed landscaping element. Ensuring adequate water retention requirements are met will aid the long term survival of the vegetation whilst adequate drainage provisions will prevent pooling and in turn prevent the vegetation becoming saturated.

Please note; Irrigation will be required immediately after installation. For further information please contact Permaroof UK direct.

Geographical Location

Geographical location and orientation are also an important part of designing the roof. Which area of the country and amount of average rainfall in that area determines the type of uses and needs for the Green Roof. Biodiversity and drainage are then designed into the roof from these requirements. The direction in which the roof faces and amount of sunlight the roof receives helps determine the types of vegetation for a successful roof.

15. The Future

As the worlds begin to understand climate change is happening and something needs to be done the awareness and understanding of Green Roofs is increasing. This is helped by events including “World Green Roof Congress” the development of Green Roof organizations such as “Living Roofs” and research centre’s like Sheffield University who are developing Green Roof exhibition centre’s and forums.

Unlike our counterparts in Canada, America and mainland Europe the Green Roof policy is not part of our legislation yet but it is coming!

New reports that have recently been released have announced that by 2015 there has to be zero storm water run of rate for all new buildings.

There are local authorities and developers in the UK who recognize the importance of the Green Roof system in the fight against climate change and the need for sustainable urban drainage systems. They are proposing Eco friendly plans to put Green Roof into policy

Sheffield development framework (part of Sheffield city council) have already consulted on “Emerging options” for new policies and are now consulting on preferred options

Option 1 Green Roofs will be required only on medium or large developments within 100mtrs of the green belt, green network, waterways, and parks and open spaces greater that 1 hectare.

(Medium or large = non residential developments over 1000sq meters and residential over 10 dwellings)

Option 2 Green Roofs will be required on all medium and large developments.

Option 3 Green Roofs will be required on all developments.

As all parties ranging from manufacturers and suppliers to local authorities and developers continue to work in conjunction with one another, the future expansion of Green Roofs within the UK is inevitable.

16. Summary

Overall Green Roofs offer a wide range of social, economic and environmental benefits. These range from significant ecological issues, such as helping to mitigate climate change, whole-life cost benefits or something even simpler, such as “it looks nicer than a traditional roof”. Whatever the key influences are, it looks like a Green Roofs within the UK are set for a sustained period of growth.

Going forward Green Roofs will not just look to attenuate water but will reduce flooding and erosion. These will provide an alternative beneficial solution to SUDS TANKS.

The purpose of this booklet is to help give an overview of key factors to take in to account when purposing, designing or specifying a Green Roof. Seeking advice from the experts is essential to the projects success. Therefore next time you are thinking of incorporating a Green Roof system into a new or existing development don’t hesitate to contact Permaroof UK direct and let us assist you through every stage of the process from design through to installation.