Green Roofs

Green roofs, vertical gardens, and green facades are among the most interesting building trends in recent years, although their history is much longer. Ecological spatial solutions are popular in many European countries. Norway, Denmark, Switzerland, and the Netherlands are the leaders in this area. However, Poland is also starting to "green up." Last year, many new and interesting solutions in this area appeared on our market.

The attractive appearance of green roofs is not the only advantage of this solution. Economic and ecological aspects are also key drivers.

Green roofs respond to rapidly advancing climate change. In the concrete centers of cities made up of buildings, squares, and sidewalks, so-called urban heat islands form, which accumulate high temperatures. Green spatial solutions are an effective method for lowering temperatures in city centers. Another important benefit is the space they provide for insects, birds, and small animals.

Greening public spaces also positively influences the well-being of residents. Green spaces serve as great recreational areas. They also improve air quality. Green spatial solutions have started to receive increasing support from local governments, which results, among other things, in property tax exemptions.

Due to all these positive aspects, in the coming years, we will likely see the development of more green facades, roofs, and courtyards.

What are Green Roofs?

Green roofs are surfaces separated from the ground by a building or other structure. It might seem that green roofs require height, but they are often located at ground level. Often, we walk on green roofs without realizing it, for example, when there is a parking lot beneath us. Unusual types of green roofs include football stadiums, grass-covered railway tracks, certain sidewalks, and patios in residential complexes.

Functional roofs can be created anywhere, but they are especially effective in cities where greenery is lacking. Interestingly, so-called green roofs are not always green. While they are most often covered with vegetation, they can also be spaces such as cafés, parks, or outdoor gyms.

Are Green Roofs Durable?

Green roofs improve the lifespan of the roof itself. One of the main factors negatively impacting roofs is daily temperature fluctuations. In the case of functional roofs, the temperatures fluctuate much less. Traditional roof coverings last 15-25 years, while professionally constructed green roofs can remain in good condition for at least 40 years.

What Plants Can Be Found on Green Roofs?

It depends on whether we choose to build an extensive or intensive roof. Extensive roofs have less substrate (soil), so not all plant species will have space to root and grow. When choosing this option, it’s better to avoid plants that require special attention. Various grasses are not a good choice in this case because they will struggle to root, and we will face difficulties mowing them in hard-to-reach spaces. For extensive green roofs, low plants such as succulents, mosses, sedums, and some herbs work best because they have low water and soil requirements.

Intensive green roofs, located in accessible spaces such as patios or above a garage slab, provide more options for plant selection. In this case, we can afford grasses, flowers, shrubs, and even trees.

Types of Green Roofs

Green roofs can be divided into three types: extensive, intensive, and semi-intensive.

An extensive green roof places minimal load on the structure and requires little maintenance. This setup does not require additional irrigation and serves as a good alternative to gravel surfaces. For such a space, we use a sedum mat of 2.5 cm thickness, a soil substrate from 6 cm to 10 cm, and a retention mat (which accumulates water and drains excess into the waterproofing layer).

An intensive green roof is the most desirable space for us. Our first thought about green roofs often leads us to garden architecture. These roofs can be used for recreational purposes. We have a much wider choice of plants that can be used for planting, and with the appropriate thickness of vegetative layers, we can even plant trees on them. In this case, a substrate layer of at least 20 cm thickness is applied, and its height, depending on the type of planting, can even reach 200 cm. It is also necessary to apply drainage with increased water retention, such as Delta Floraxx 40H with an accumulation of 19.59l/m2.

A semi-intensive green roof is a cheaper and less demanding alternative to an intensive green roof. It is usually covered with grasses, perennials, herbs, mosses, and shrubs. It has less diversity in use and shaping.

We also categorize green roofs based on the thermal insulation layer, i.e., traditional green roofs and inverted green roofs. There is also a division based on the slope angle into flat and steep green roofs.

Layers of a Green Roof:

What are the layers of a green roof?

The initial layer is a root-resistant waterproof insulation.

Depending on the needs, we can apply EPDM film, TPO/FPO membranes, bituminous coatings, or roofing felt at this stage.

Next, the waterproofing must be protected from mechanical damage using protective geotextile, typically PES/PE with a grammage less than or equal to 300 g/m2.

On inverted green roofs with XPS thermal insulation, we apply a diffusion mat. Its purpose is to separate the thermal insulation from the water retention and drainage mats, for example, the Delta Vent RR diffusion-separation mat.

Next, we apply a drainage layer. The outlets are used to remove excess water and collect water for plant growth. We can use HDPE water retention-drainage mats, EPS (expanded polystyrene) bucket mats, HIPS water retention-drainage mats, PP retention boxes, or mineral drainage. These materials are characterized by retention capacity, drainage ability, and compressive strength.

The next step is to apply a filtration layer that separates the drainage layer from the vegetation layer and prevents particles from flowing out. We use PP filtration geotextile (100-200g/m2).

The final layer where we will plant vegetation is the vegetation layer, which consists of specialized substrates. Their composition varies depending on the type of green roof we have chosen, which also determines the choice of plants.

What products do you need?

• Waterproofing: TPO/FPO membranes, EPDM films, bituminous coatings, roofing felt (for intensive green roofs, the waterproofing must be root-resistant, so EPDM films are recommended)
• Protective geotextile PES/PE
• Thermal insulation XPS
• Diffusion-separation mat (Delta Vent RR)
• Drainage layer with filtration geotextile (Delta Floraxx Top)
• Substrate appropriately selected for the type of roof

If you want to buy other Dorken brand materials, please contact us +48 697 691 472, +48 883 292 303.