Designing the Right Green Roof System

Design Considerations

The popularity of green roofs within the built environment has increased dramatically over recent years, with their inclusion in both urban and rural projects now being mainstream. Although the basic categories of green roofs have remained un-changed over the years, the development of different types of systems and the plant species within them has progressed as more experience has been gained.

There are a number of different types of garden roof, defined by the way they are used. The basic types of green roof fit into either extensive or intensive categories, but there are also those which are a hybrid of both - these types of systems could be termed semi- extensive or semi-intensive.

  • Intensive or Extensive – What’s Best For Your Project?

    The table below provides a comparison of some of the differences between intensive and extensive green roof systems.

    Intensive Green Roof Systems Extensive Green Roof Systems
      intensive-green-roofs Extensive-green-roofs
    Usage: Generally as a recreation space Generally for visual / environmental / biodiversity
    Landscaping: Trees, shrubs, lawn turf, hard landscaping Sedums, wildflowers, grasses, mosses
    Maintenance: Regular maintenance required Minimal requirement
    Irrigation: Regular irrigation required. Usually dedicated systems installed Only generally required during the establishment phase, or in times of prolonged drought conditions
    Build-Up Depth: Typically around 200mm - 1.0m Typically around 80 - 200mm
    System Weights: Typically 150 - 1000 kg/m² Typically 100 - 180 kg/m²
    Roof Slopes: Less suited to sloped roofs Suitable for flat or pitched roofs (with suitable retention systems in place)
    Water Attenuation: Greater water attenuation due to deeper substrate depths Less water attenuation due to shallower substrate depths
  • Selection of Underlying Waterproofing Systems

    The waterproofing is paramount to the success of a green roof. It has a fundamental requirement to prevent water ingress into a building and resist damage from root penetration. The roofing system also provides thermal performance, roof drainage falls, air tightness and vapour control to the building.

    Icopal can provide traditional high performance multi-layer reinforced bitumen roofing to innovative synthetic single layer energy efficient solutions designed for the most complex building forms. Our roofing products combine fully guaranteed membranes manufactured on high performance polyester and glass fibre reinforcements, and can be applied using a variety of techniques.

    Icopal's experience in waterproofing technology allows us to deliver the correct specification of roof membrane and system to suit the criteria of the green roof project based on the choice of landscaping, performance and robustness required.


    Reinforced Bitumen Membranes

    A multi-layer elastomeric Reinforced Bitumen Membrane (RBM) system incorporating the Rootbar Capsheet provides a high performance and extremely robust waterproofing system suitable for use under a wide range of green roof systems.


    Reinforced Bitumen Membranes for Green Roofs



    Single Ply Membranes

    Sureplan FPO and Monarplan PVC single ply membranes provide a lightweight high performance waterproofing option. The nature of single-ply membranes makes them more suited to extensive roof systems. Green roof waterproofing systems using Icopal Universal WS combine the benefits of a single layer membrane with the robustness of a bitumen membrane.

    Sureplan FPO and Monarplan PVC single ply roofing membranes

    Single Ply Membranes  for green roofs



    Liquid Applied Roofing

    Elastoflex cold applied liquid waterproofing offers environmentally considerate and flexible solutions to previously frustrating and difficult waterproofing problems.

    Elastoflex cold applied liquid waterproofing
    Liquid Applied Roofing for green roofs

    Hot Melt Structural Waterproofing

    The Parabit Hot Melt Structural Waterproofing System offers a seamless highly elastomeric bitumen waterproofing option ideally suited beneath large area intensive roof systems and podium decks.

    Parabit hot melt structural waterproofing
    Hot Melt Structural Waterproofing systems for green roofs

    Icopal Guarantees

    As a world leader in the manufacture of waterproofing membranes, we pride ourselves on offering the most comprehensive guarantees available in the flat roof industry, giving further reassurance of our commitment in providing total confidence in our range of high performance waterproofing membranes.

    Icopal guarantees incorporate a range of features and benefits tailored to suit the client’s specific requirements including materials, insurance backing, design, consequential damage and approved installation. All guarantees offer up to 20 years as standard, subject to specification.

    Icopal insured guarantees incorporate a range of features and benefits
    Read more about Icopal Insured Guarantees

    Approved Contractors

    Installation of the Icopal Green Roof System is carried out exclusively by a network of trained and approved contractors who can demonstrate excellence in all aspects of roofing and landscaping.
    Using an Icopal Approved Contractor ensures quality right from the start giving you access to a wealth of experience and technical skill protecting your investment with unrivalled guarantees.

    Icopal green roofing approved contactors
    Icopal Approved Green Roof Contractors
  • Design Considerations For A Successful Green Roof

    For a green roof to flourish it requires suitable amounts of sunlight, water, sufficient drainage and aeration to encourage healthy plant growth. To deliver a successful green roof the designer must consider the building's position and location, along with the orientation of the roof during the day and any shade from surrounding buildings. The roof's height can have an affect due to wind action, and can cause wind scour of the substrate. Pebble borders are generally used to avoid this.

    The additional weight loading from a green roof is a major factor to consider as the structure must have sufficient load bearing capacity to support a water saturated green roof system. The roof must have sufficient drainage which will help reduce the imposed loads and prevent excessive saturation of the growing substrate which can lead to deterioration of the planting.

    A green roof will require regular safe access for maintenance and it is important that adequate fall protection measures are put in place to allow for safe inspection and maintenance of the roof.

    The waterproofing system is paramount to the success of the green roof, as it is fundamental to prevent water ingress into the building. Many BMI waterproofing systems are suitable for use beneath a green roof and it is essential, when designing the roof details, that all adjacent building elements and interfaces are considered.

    Green roofs will require water and provision for irrigation should be considered at the planning stage. All Green roofs will require irrigation during the establishment period and so a temporary water source should be provided. Intensive roof planting and lawns will require a permanent irrigation system to keep them supplied with water during hotter, drier, summer months. Extensive roofs will only need irrigating during the establishment phase, and very little subsequently except during longer periods of drought. Pitched roofs retain less water and therefore a permanent irrigation system should be considered. 

  • Planting Schemes For Green Roofs

    Green roof systems can be established in a number of different ways which generally relate to budget, logistics and aesthetics:

    Vegetation Mats – Pre-grown vegetation mats which are laid onto the surface of the substrate are an ideal way to create a green roof that provides instant impact. This method of establishment is very common with extensive sedum and meadow systems. Of course, installing a pre- grown lawn turf is also a common method of creating an intensive recreational area.

    Plug Plants - This method uses individually planted plug plants allowing a greater flexibility in the choice of species for the green roof, and is generally more cost effective compared to using vegetation mats. However, the establishment time to get full ground cover is longer (2-3 years).

    Seed – Mixed seeds can be sown over the top of the installed substrate to create the habitat of choice. Although very cost effective, it takes several years for the vegetation to establish, therefore the combination of seed with plug planting is often used to speed up colonisation of the green roof.  


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