What is a Green Roof? What roofing materials are required? Does it worth all that trouble?

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Well, it really does! But lets dig a little deeper.

What is a Green Roof?
It is a roof which is fully covered with plants. Have you ever heard about the hanging gardens of Babylon (500BC)? In fact, the idea is ancient, but technology has evolved dramatically!

MEC's green roof
Image by sookie

The precursors of modern green roofs were the, well known in Scandinavia, sod roofs. Vikings used to plant their roofs to provide better insulation and stability to their wooden houses. Nowadays, new designs are being more and more used because of their innumerable and versatile other advantages they provide.

The first country to introduce the modern green roof "trend" was Germany in the 1960s. Today 10% of Germany's rooftops are "green". Gradually, other countries followed Germany and today green roofs are getting popular in mainly Europe and America. This, relatively new technology, is considered to provide the sustainable energy designs because it helps preserving energy for a building's needs.

Alternative names include eco-roof, grass roof, vegetated roof, living roof etc.

What is the difference between a green roof and a roof garden?
Lots of people think them as the same thing. In fact there is a great debate on this. We consider them as two different designs. A green roof requires a complicated, multi-layer structure to support it. The hole roof is covered with soil were plants grow. On the other hand, vegetation is planted in pots to form a roof garden, which is basically used for its aesthetic beauty.

What are the types of green roofs?
There are two different categories:
  • Intensive
    Larger plants and little trees require deeper soil. Thus, this design comes with at least 30cm of soil which adds extremely high weight to the building. In addition, these plants need a lot more water and gardening. Intensive roof structures are usually used for decorative purposes.

  • Extensive
    When a green roof is built to provide its technical, economic and environmental advantages, we prefer the extensive design. This type of roof construction uses vegetation like grasses and flowers, which require less watering and more lightweight soil. Moreover, it is worth to mention that extensive designs require a minimal maintenance while they provide uncountable benefits. Of course, each roof is designed uniquely to me consistent with the requirements of the area, the environment, the local law etc.

A green roof at Vancouver

How is a green roof built?
These designs require a lot of different roofing materials.

  1. Waterproofing Layer
    Any waterproofing material can be used here. It might be the most important thing to have in mind when building a green roof. If there is a leak here, you will have to rebuild the hole structure from the beginning.

  2. Root Barrier Layer
    This layer is usually not used in extensive structures. Although, it is absolutely critical to install it on an intensive roof design where plant roots are really mean. It will prevent the roots from penetrating the waterproofing layer and messing up the job.

  3. Insulation Layer
    Some of the greatest benefits of eco-roofs are the perfect heat, noise and water insulation. This layer will keep the building warm during the winter and cool during summer. If someone can not afford a special insulation material, an air gap will do a relatively good job. Avoiding this layer will affect the roof's overall performance but it won't be disastrous.

  4. Water Retention Layer
    This layer is only used when vegetation planted requires additional water supply. A moisture mat will be ok for these purposes.

  5. Drainage Layer
    A drainage layer is absolutely necessary. It stores the water needed for the plants to grow while it provides proper aeration to the soil beneath.

  6. Filter Layer
    The filter mat is there to prevent soil from entering the drainage layer. Otherwise, the moisturising and aeration won't work appropriately.

  7. Soil
    The soil used shall be selected very carefully. Firstly, it has to be lightweight in order that the building can support the extra load. Also, the type of soil and nutrients it will provide, absolutely depend on the local weather and the vegetation indented to be used.

  8. Vegetation
    Now, the last layer. Remember that all the structure is there to support this layer. Vegetation must be chosen in order to fit the roof's micro climate. Plants have to be resistant to frost, drought and wind. They also have to be shallow root, regenerating and generally durable to all weather conditions. These factors will form a perfect ecologic and energy saving roof that will need minimal maintenance!

Green Roof Layers

Any disadvantages?
Every structure has both some advantages and disadvantages.

  • Difficult construction
    A small mistake might mess up all the construction. Thus, Green roofs require experienced stuff to build them.
  • Weight
    Some older buildings might not be able to support the extra weight. Before considering to build an eco-roof, you should check the building's specifications.
  • High initial cost
    Because of the great quantities of roofing materials, green roofs are more expensive than conventional solutions. However, if we consider the energy savings they provide and their longer life, everyone can tell that they are economically profitable as well.


    • Air Quality
      The plants on the top of the roof will filter the polluted, dusty, foggy, toxic air. Moreover, when they photosynthesise, they absorb the CO2 and produce oxygen.
    • Reduce the urban heat island effect
      Plants absorb the solar energy to photosynthesise while cooling the building via evaporation. The hole structure reflects the most of the rest heat back to the atmosphere. Thus, the heat is not stored into the concrete, resulting in the roof cooling during the night hours.
    • Support flora and fauna
      Vegetation on rooftops will provide natural habitat for birds and other animals in the large cities.
    • Lower CO2 emissions
      Because of the better insulation and cooler micro-climates, buildings with a green roof installed will need less energy for heating and cooling purposes. Thus, they will contribute in less CO2 emissions and a healthier planet.
    • Lower long term costs
      The multiple layers placed, protect the conventional roof. Thus, you save maintenance expenses and it occurs in longer roof lifespan.
    • Energy savings
      Ultra high insulation levels will decrease the heating and cooling costs throughout the year. It is worth to mention that "Environment Canada" found that a grass roof with 10 cm of soil can save up to 25% of summer cooling energy needs.
    • Higher building value
      A green roof may add up to 6-15% to the buildings value according to studies in the US and UK.
    • Insulation
      Insulation acts in two ways. Firstly, it is a great thermal and sound barrier for your house. Last but not least, the more stable temperatures provided, decrease the thermal contraction and expansion of the concrete layer of the roof. Thus, it protects it, resulting in longer lifespan and lower leaking possibilities.
    • Water management
      Some cities have huge problems with their storm-water management. These roofs will reduce the waste-water flowing into the sewerage system.
    • Sound insulation
      Not only they are suitable for thermal insulation, but they act as a good sound barrier as well. Researches show that a 12cm soil roof can achieve up to 40db of noise reduction. So, if you live near an airport or in a crowded city, you might want to think it again to install a grass roof.
    • City view
      The city where most of buildings have installed green roofs is more beautiful from above.
    • Family/Employee recreation
      It is a good idea to have go for a picnic during a nice shiny day. Also, companies that have installed a grass roof, have recorded increased productivity. This happens because employees go there to have a break and relax when they feel stressed.
    • Food Production
      If we are talking about your house, you can grow your own biologic vegetables for free on your roof. However, bigger roofs may support larger areas's needs. This helps in fresher and cheaper vegetables and it supports local economies.

Note that governments provide renewable energy funds to help you install systems like this. You may use a fund provided for green roof systems, or if it is not provided, get advantage of a fund covering extra insulation or energy saving systems. The only sure thing here is there are plenty advantages to get advantage of!

Need more information about green roofs?

P.S. Best rooftop designs may combine two or more green energy technologies to support the sustainable energy development. Along with your vegetated roof, consider installing some photovoltaic panels, solar water heaters and a windmill. It is surely worth the trouble.

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