Green roofs create comfort and improve air quality

BMI Icopal's green roof solutions provide unlimited new possibilities for construction. For self-builders, the so-called steep green roof is a suitable solution, and professionals can also install various types of sloping green roof solutions.
Extensive green roof

A green roof is more than a roof

Green roofs are an increasingly attractive solution for both urban and domestic buildings. They absorb carbon dioxide and produces oxygen, improving air quality. They can serve as a habitat for rare plants and provide a habitat for beneficial pollinators. A green roof is also a sensible technical solution.

The roof no longer has to be just a roof, but can be the crowning glory of a building - or blend beautifully into its surroundings. In dense urban development, it is possible to make use of the roof of a building by constructing, for example, a lounge area, such as a green oasis, to make the inhabitants more comfortable. In the courtyard, the green roof acts as a pleasant extension of the garden.

Benefits of a green roof
  • More environmental comfort

  • Binds stormwater

  • Cools the air in heat islands

  • Protects the roof waterproofing from mechanical stress

  • Supports biodiversity

Green roof for all roofs

Steep green roof - green roof for gable roof

A steep green roof is a personal eye-catcher in detached houses, terraced houses, carports or sauna huts.

A steep green roof adds greenery to the yard. It absorbs rainwater, allowing it to run off and evaporate from the roof in a slow and controlled manner. This in turn prevents flooding of the yard, for example in asphalted yards. The soil layer of the green roof insulates heat, thus equalising the temperature of the space below in summer and winter.

The structure of a steep green roof

The waterproofing of a steeply pitched green roof is usually done with a single rubber bitumen core. On top of this, a root protection layer is installed, which can be root-protected rubber bitumen or other strong root-protection membrane. A drainage sheet is installed on top of the root protection layer.

BMI Icopal's Fonda Green drainage sheet acts as both a drainage layer and a root protection layer, so no separate root protection layer is needed. On steep roofs, it may be necessary to support the soil layers, for example with battening, so that the substrate does not run off.

Gently sloping green roof

A gently sloping green roof can be installed on the roof of a market, a residential building or even a carport, for example. The picture shows the sloping green roof of the Heinola Bird Garden - it fits naturally into the environment.

The green roof equalises the temperature of the air below and at the same time protects the waterproofing layer of the roof itself. In housing associations, for example, a car roof with a liverwort roof is also beautiful to look at from the top floors. In the rain, it absorbs water and thus prevents flooding of the yard during heavy rains.

How to make a green roof: the structure of a loose green roof

On a sloping green roof, waterproofing is generally provided by three layers of rubber-bonded waterproofing layers, the top layer being root-protected. A drainage and water retention layer is installed on top of the waterproofing layer.

The water-retaining layer can be, for example, a thin layer of rock wool. The waterproof layer is to be topped with a substrate and selected vegetation, such as liverwort or meadow grass. The design of a sloping green roof can be, for example, a sloping pent roof or a so-called flat roof that tilts inwards.

Inverted green roof: courtyard deck and roof garden

The thick layer of soil in an inverted green roof, such as a courtyard deck or a roof-top urban garden, allows for a wide variety of vegetation. It provides good sound insulation, effectively absorbs rainwater and balances the temperature of the space below.

Of course, more demanding plants need more care - watering, fertilising and, if necessary, cutting back lawns, trees and shrubs. A rooftop garden in the city is usually a joint project between the residents of a housing association or a landscaper of a public space.


Garden cover, green roof inverted structure

The structure of the waterproofing of a pitched green roof is very similar to that of other sloping green roofs.

In the inverted construction solution, waterproofing layers are topped with water-resistant thermal insulation and a drainage layer between the waterproofing and the thermal insulation.

Green roofs are always built according to the type of roof

You can build a green roof on practically any kind of roof. The most important thing is to build your roof carefully, professionally and with quality materials. On flat and sloping roofs and steep pitched roofs, different materials and construction solutions are used for waterproofing. 

A drainage layer is placed on top of the actual waterproofing layer of the green roof. It acts as a water reservoir for plants and ensures that excess water can safely escape from the waterproofing layer. 

Loose green roofs should always be installed by a roofing professional with a firefighter's certificate and knowledge of waterproofing. You can build a steep green roof yourself if you wish, as the materials used do not require the installer to have a firefighter's licence. However, experience with roofs and construction is an advantage. The installation instructions must be followed carefully to ensure that the green roof works. On steep roofs, it may be necessary to support the soil layers, for example with battening, so that the substrate does not run off. 

In green roofs and roof gardens built on courtyard decks, the movement and thicker growing medium puts a strain on the structures. Their waterproofing layer is protected underneath the thermal insulation. This is called a reverse green roof solution. 

Courtyard decks and roof gardens require load-bearing capacity from the structures below. For these green roofs, it is particularly important that the waterproofing is done correctly. For inward-pitched green roofs such as garden decks and roof gardens, several layers of bitumen are used as waterproofing. These green roofs are best left to a professional to design and build.

Benefits of a green roof 

  • Improves amenity, is beautiful to look at and creates opportunities for urban farming

  • Produces oxygen and cleans the air, trapping dust, emissions and carbon dioxide

  • Binds rainwater to help manage stormwater and prevent flooding

  • Equalises the temperature of the space below and the ambient temperature in urban heat islands

  • Extends the technical life of the roof by protecting the waterproofing of the roof

  • Can maintain biodiversity by providing a habitat for rare field plants and the insects that benefit from them


Green roofs are easy to maintain and check

Green roofs are easy to maintain, but they also need regular maintenance. Selected plant species can be allowed to take over naturally from the roof. Regardless of the type of roof, excess tree trunks and, in cultivated areas, weeds should be removed. Of course, you can let various weeds grow freely on the roof of a wild sauna hut if you wish. 

Caring for green roof plants

Green roofs - including liverwort roofs - should be watered during the dry season. Proper fertilisation of plants contributes to their well-being. Liming the liverwort cover every four years or so is good for liverwort. Otherwise, liverwort can manage with a little fertilisation. However, spring fertilisation can encourage liverwort to flower. In autumn, it is a good idea to remove excess leaf litter and conifer needles from the roof to prevent them from acidifying the soil too much. 

Also check your green roof twice a year

Green roof technology should be checked twice a year. Check the roof gutters on sloping roofs to ensure that water can move freely through them. In some models of roof wells, it is also possible to check the condition of the waterproofing and seams at the same time. The gutters of a pitched roof or other steep roof are inspected and cleaned of debris. 

With a thin layer of thatch, the condition of the waterproofing can be easily checked by lifting a piece of thatch from the roof. After the check, the piece of cabbage is put back in place.

Is the green roof leaking, are the plants drying out? Green roof problems and how to avoid them

Those considering a green roof may fear that the structures will not be able to support the weight of the roof, the roof will leak or the plants will not grow properly. However, problems with green roofs are rare when the weight of the roof, waterproofing and growing medium are taken into account during the design and construction phase. 

Structures are designed to withstand the weight of the green roof even when wet

Roof gardens and courtyard decks are generally built on new sites where the structural engineer has pre-designed the structures to withstand the weight of the green roof, both dry and wet. The load-bearing capacity of the structures must be ensured in the renovation project. For example, a liverwort roof is thin and does not require exceptional durability from the underlying structure. This also makes it a safe option for roof renovation. 

Quality installation is key

Correct installation is the key to waterproofing green roofs. Particular attention is paid to the careful execution of the various joints and seams. A green roof is actually a very durable solution as a waterproof roof: it protects the waterproofing layer from UV radiation and mechanical stress, unlike a conventional roof. 

Heinolan lintutarha viherkatto

A constant moisture level in the growing medium during planting and sowing is ensured

To ensure that the plants start growing, the substrate must be of the right quality and evenly moist at the sowing and planting stage. The growing medium should be kept moist until the plants have taken root. Properly rooted plants are more drought-tolerant in the future. 

Sometimes not all the plants chosen for a roof will thrive on that particular roof, for example because of varying light conditions. Then you can try planting new species - or let the ones already on the roof take over freely.

Old idea, new uses 

Wildly flowering or subtly green roofs have been built throughout the ages. Finland has decades of experience with modern green roofs. Very few problems have been found with the waterproofing of roofs. A green roof is a very durable, safe and attractive roofing solution when designed and installed correctly and with quality products. 

BMI Finland has been supplying and installing waterproofing for green roofs for decades. We have expertise in the best products, different construction solutions and waterproofing installation.

Green roof price

The price of a green roof depends on the size of the roof, the steepness, the structural solution chosen and the vegetation. You can build a green roof for a domestic rubbish shed or a bike shed in a housing association on a small budget. In new urban developments, the price is also influenced by the future use of the roof: whether you want a liverwort roof, a grass roof or a diverse garden. 

When drawing up a budget, it is essential to take into account the benefits of green roofs as a source of clean air, a source of human comfort and a source of environmental diversity. 

If you would like more information or ideas for your own green roof plans, please feel free to contact us!

Are you planning a green roof or patio deck? Contact us

Green roof waterproofing from Icopal Katto Oy

BMI Icopal's contracting company Icopal Katto Oy has decades of experience in installing waterproofing for various types of green roofs. For example, the waterproofing of the green roofs in the Tripla block in Pasila, Helsinki, was installed by Icopal Katto Oy.

If you want a green roof or patio cover for your property, with reliable professionalism and the best products on the market, ask us for more information.

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Our authorised contractors also serve in green roof installations

BMI Finland also has a comprehensive network of accredited, experienced roof waterproofing contractors.

Ask one of our partners about the installation of green roofs or other bitumen roofs. You get quality products installed by skilled professionals for your green roof.

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Help with green roof design

Structural engineer, if you need help designing a green roof, we're happy to help. Together, we will find the best green roof solution for your specific needs.


Designer, use ProdLib to get the finished delta images of the green roof structure

ProdLib is a product library with ready-to-use detail drawings to help architects and designers. BMI Icopal's ProdLib product library provides you with ready-to-use CAD images of the best structural solutions for green roofs and garden decks, for example.


FAQ about Green Roofing

A green roof is a flat or sloping roof covered with vegetation. When building a green roof, it’s important to think about its composition, which must be made up of layers of different but interacting materials to ensure

  • water accumulation

  • water tightness

  • protection against root action

  • mechanical protection

  • draining and filtering activity

  • nutrients get to the plants.

Green roofing has a lot of benefits when it comes to dealing with sustainability, the environment and climate change concerns, particularly smog and pollution. These benefits include

  • encouraging wildlife: rooftop habitats can provide a 'green link' that connects natural pockets of habitat to each other. They can also provide isolated habitats that are not disturbed by other green areas at ground level

  • improving air quality: green roof plants improve air quality by absorbing atmospheric carbon dioxide and releasing oxygen.

  • improving temperature regulation: through the daily cycles of condensation and evaporation, plants are able to cool and humidify the surrounding air, improving the microclimate

  • reducing and slowing stormwater runoff: in urban areas in certain climates, green roofs can retain nearly all storm-related water during the summer months, and up to 20% during the winter months.

It is often best to plant species on a green roof that require minimal maintenance. Vegetation composed of sedum essences can survive extreme drought and easily regenerate and self-propagate.

Green roof design can also include Blue Green Roof technology, which offers all the performance features typical of green roofs while offering the possibility of storing, conserving and reusing rainwater. It is also a useful solution for reducing the effects of extreme rainfall that can cause localised damage.

When it comes to choosing roofing materials, strong, durable and - more recently - eco-friendly characteristics are most often selected. These traits are available in both materials and solutions. For example:

  • wooden shingles: these are shingles made from shredded wood from controlled forests

  • slate and clay roof tiles: terracotta roof tiles are made from porous ceramic with clay as its base. Clay is a natural material and has been used in the building process for centuries due to its durability and low maintenance

  • solutions with unique characteristics: such as Noxite bituminous waterproofing membranes, which not only provide a high-quality flat roof, but reduce pollution by using the sun to transform harmful nitrogen oxides (NOx) into harmless nitrates, which are washed away by the rain. Noxite is a highly effective means of reducing the ongoing environmental impact of a building as it continues to function throughout the life of the roofing membrane 

  • green roofs: the green roof solution reduces the heat island effect, boosts the insulation capacity of the environment below and improves air quality

  • cool and white roofs: these reduce roof radiation by reducing overheating and so the air conditioning required.

The price of a green roof depends on the size of the roof, the steepness or pitch, the type of green solution chosen and the vegetation planted. When considering the cost, remember to take into account the benefits of green roofs as a source of clean air, emotional wellbeing and environmental diversity.

If you’re investing in a green roof, it’s important to know exactly what the benefits are so that you get a great return on investment:

  • roof membrane protection: vegetation on a roof deck protects the roof surface from the extremes of weather, temperature and UV radiation, which can significantly increase its lifespan

  • reduced storm water run-off: water is stored by the green roof substrate and then taken up by the plants, where it is returned through transpiration and evaporation into the atmosphere. The drainage layer in green roofs also delays the rate at which water run-off occurs, reducing stress on drains and sewers during heavy rainfall

  • reduced energy costs: the layers of a green roof system improve the thermal performance of the roof, helping to keep the rooms below cool in summer and warm in winter (although this effect is generally not included in any U-Value calculations).

Green roofs can extend the life cycle of a roof for more than 30 years as its layering makes it more durable than normal roofs. It is important, though, that the membrane and the stratigraphy (or layers) are correctly installed.

A flat roof usually has an average lifespan of about 15 years. Many of its components require maintenance from time to time and, if this is not done, the roof can be damaged by infiltration. To make the roof last as long as possible, it is important to carry out frequent inspections and work on the drainage system.

The health of the roof changes over time depending on the attention you give it. To ensure high quality roof products remain fully functional over decades, it is essential to follow a regular maintenance programme.

Maintenance problems normally include infiltration, cracks in the roof covering or tiles, deterioration of the membranes and insulation. If not repaired, the roof's insulating performance will decline.

Inspect your roof after storms and high winds, and at major discontinuity points, and clean it periodically.

And remember to check your product’s warranty, whether you have installed just a few tiles or an entire roof system. A good warranty can protect you from costly repairs in the future.

A green roof is a surface that needs to be made waterproof to avoid damage from water seeping in. So, it is essential to have an anti-root membrane and a draining layer that will help carry away excess water from the rain or gutters. 

Then, adding a drainage mat and felt layer will allow the water to pass through and the roots to attach themselves to the growing medium. The drainage layer will then provide the growing platform for the green roof. The composition of the soil is also important as it aids proper plant nutrition and growth. 

Finally, the roof must include an irrigation system, possibly water-based, so as not to overload the roof, and reduce water consumption and waste. 

If you choose an intensive green roof, you can plant classic garden plants, both herbaceous and shrubs. If you opt for an extensive green roof, low-lying and creeping plants are best as they are suitable for growing in thin layers of substrate.

A blue roof can be key to sustainability in buildings, particularly in urban areas where a ground level solution may not be possible due to lack of space. Benefits of a blue roof include

  • temporarily store rainfall to reduce runoff

  • reduce the flow rate of water from the roof

  • store water for reuse in other areas of the building, such as irrigation or cooling

  • make up the drainage and support layers for green roofs

  • Easy to maintain.

If your business is located in an area particularly prone to flooding, then a blue roof system can also help to protect your building (and neighbouring ones) from damage.

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