Biodiverse green roof: Phase 5 of the greenIZOLA project

. Cities represent a massive area of dense materials that accumulate heat, do not retain rainwater, and therefore create an unpleasant condition for life. Many countries apply green roofs as an effective and practical tool to mitigate the adverse effects of urbanization. They are often designed as intensive and extensive. In recent years, a lot of research has been done on green roofs for a better understanding of their behavior in different conditions. In recent years, experimental green roofs have also started emerging in Slovakia. At the same time, the idea of restoring vegetation to industrial zones with help of such construction was made. The paper focuses on the latest planned phase of the project for the greening of an office building with an adjacent area in an industrial zone. Phase five consists of the design of a biodiverse green roof that will provide an alternative habitat for fauna and flora. The main elements of the design are the compositions of green and wetland roofs. Moreover, the paper summarizes the already implemented phases of the project.


Introduction
Vegetation in cities is an essential element that improves living conditions in metropolises.However, in some cases, it is not easy to preserve it and support urban development at the same time, which is why green roofs have been used frequently in recent years.Placing vegetation on the roof partially helps to restore the vegetation previously built over.Green roofs are often designed as extensive, for a smaller substrate thickness of 80 -150 mm and minimal maintenance.Semi-intensive roofs are designed with a substrate thickness of 150 -300 mm and must be irrigated, especially in hot and dry months.The selection of vegetation is more diverse with an intensive green roof, thanks to the greater substrate thickness of 300 mm and more, although such a roof requires more maintenance [1].Special green roofs have started to be implemented nowadays, such as a biosolar roof (the combination of solar panels and a green roof) or wetland roofs (the application of wetland vegetation).The green layer is designed so as to create suitable conditions for vegetation growth and, at the same time, to impose the least possible load on the structure [2].
Many countries are taking a solid initiative to apply green roofs to new and existing buildings through reward or penalty.They use them as an effective and practical tool for urbanisation.The composition of a green roof can retain a large amount of water and, as a result, delay stormwater runoff.Several researchers have studied the issue of rainwater accumulation in their region and found out that this ability of the roof varies mostly from 55% to 88% [3].Besides, using the retained water in evapotranspiration is possible, which produces a cooling effect on the building and the surroundings.The substrate and vegetation have a higher albedo than, for example, asphalt strips; thus, part of the incident radiation can also be used for photosynthesis [4].Hence, the waterproofing layer is protected from UV radiation and climatic influences.In terms of greening, a green roof can increase the abundance and diversity of birds, arthropods, and gastropods more than a conventional roof in the city [5].It is this added value of the roof biotope that is the reason for the implementation of green roofs in many European cities [6] with declining vegetation.Last but not least, such a roof also brings aesthetic benefits to the building and the surroundings.Its spaces can serve for relaxation and psycho-hygiene in a built-up city.
Green roofs are often applied in city centres, on houses, apartment buildings, offices, and commercial buildings.However, they are only found in small numbers in industrial zones.These zones are growing along with the developing city.They represent a relatively large part of the city built-up primarily for the production, storage, and handling of materials.Therefore, it is necessary to design and introduce green infrastructure elements even in such parts of cities.
The paper presented is dedicated to the next planned phase of the greenIZOLA project, where vegetated structures are used for the green conversion of a site in an industrial (grey) zone.Once all the planned phases are completed, an increase in vegetation area from 14% to 41% should be achieved.The subject of the solution is the most extensive terrace in the building, which by its dimensions, offers space for the creation of a combined green roof, providing an alternative habitat for flora and fauna.

greenIZOLA project
The greenIZOLA project aims to return vegetation to the industrial zone using green structures.The project is supported by the APVV-18-0360 ACHIEve Active Hybrid Infrastructure for a Sponge City project.The subject of the solution is an office building with adjacent area in an industrial zone in Košice.The building is four-storey, made as a skeleton structure with infill masonry and finished with a flat roof.There are four terraces on the building (two, western and northern, on the second floor and another two, southern and northern, on the fourth floor).The composition of the roof and terraces is single-skin with layers in reverse order (from bottom to top: a reinforced concrete slab, a foam concrete gradient layer, a vapour barrier of asphalt strips, thermal insulation based on XPS and geotextile).In addition to the main building, there are two storage halls, three storage sheds, a fire tank, and a car park with 36 parking spaces.
The project is divided into nine phases, as shown in Figure 1.Various compositions of green roofs are used, including their special types, such as biosolar and wetland roofs.Moreover, the creation of a green wall on the eastern and southern parts of the building façade is considered.The resulting spaces can be used to research the interaction of vegetation layers with the building and the surroundings.The first phase, consisting of the construction of an experimental green roof on the southern terrace on the fourth floor, was implemented in May 2020.The terrace was divided into three test segments (TS I -a green roof with 120 mm thick substrate, TS II -a reference roof finished with a gravel layer, and TS III -a green roof with 240 mm thick substrate) [7].In May 2022 (after two years), TS II, representing the reference roof, was replaced with a wetland roof composition.The next phase (Phase 2) was the construction of a green roof on the existing shelter in June 2021.The roof was divided into three parts: a composition with a mineral wool-based growth medium, a composition with mineral wool and a layer of substrate, and a composition with mineral wool and a substrate supplemented with a biochar admixture.In July 2021, a carport with a green roof was added to the area (Phase 3).The carport protects six parking spaces and the main and side entrances to the building from rain, hail, and snow.The last completed phase (Phase 4) was the extension of the western terrace on the second floor in April 2022.The roof of the extension was finished with an extensive green roof.The remainder of the western terrace will be supplemented with a portion of the wetland and green roof.

Current condition of the northern terrace on the 2 nd floor
The northern terrace has an area of approximately 171.82 m 2 , is directly accessible from the office and the meeting room and has the best view of the terrace on the second floor.It is currently covered by a green roof made in 2010 (Figure 2).The implementation and design of the roof were conducted without in-depth knowledge of the subject or consultation with a botanist.The original roof design corresponded to the requirements for an extensive green roof at that time.It was made of layers of a drainage system, an 80 mm-thick substrate, and stonecrop plants.In addition to the vegetation part, the terrace has a walkway made of concrete tiles and concrete planters with shrubs, and the remaining surface is finished with gravel.Roof maintenance was minimal; the roof prospered relatively well in the first years; however, after a few years, the defects of the improper roof design and maintenance began to show, namely through the mortality of the vegetation.

Proposed condition of the northern terrace on the 2 nd floor
The northern terrace is the largest on the property and offers space to create a "park" with a variety of vegetation.This space should mainly serve a relaxing purpose, as intended from the beginning.Thanks to the acquired experience and knowledge, a new composition of the green roof on the terrace was proposed in collaboration with a horticultural company (layout and landscape integration), a botanist (correct selection of vegetation species, possible experimentation with non-typical species of vegetation for our climate) and a construction company (for a correct structural design with no damage to the building).Each member is necessary for the correct and efficient design of a green roof that is intended to represent a space with added value in terms of greening.The idea was to design an intensive green roof to possibly plant taller vegetation.Since it is an existing building with static limitations, the designed thickness of the substrates must be smaller than for an intensive roof.Still, the design included several elements that will be incorporated on the terrace.Figure 3 shows the terrace layout in the current and proposed condition.The terrace area will consist of three vegetation sections: a green roof with a 100 -120 mm thick substrate layer, a green roof with a 150 -180 mm thick substrate layer, and a wetland roof (Figure 4).The substrate is to be distributed unevenly to elevate the terrain gradually.The terrace will be finished with a root-proof waterproofing layer.A protective layer, drainage and water accumulation layer, filter layer, substrate, and vegetation will follow.A wetland roof shall comprise a pond liner, substrate mixture, wetland vegetation, and water.Walkway will lead through each section so visitors can walk along the terrace and use the space for rest and recreation.The terrace also includes benches, an insect hotel, a birdhouse, and concrete planters for planting shrubs.The vegetation layout was adapted to the load-bearing skeleton system of the building, with beams in the longitudinal direction and around the perimeter of the building.The part of the green roof with a substrate thickness of 180 -150 mm would generate a greater load (Table 1); therefore, the substrate distribution is proposed along the edge of the terrace near the columns and beams.This area represents 28% of the entire terrace.The second part of the green roof with a substrate thickness of 120 -100 mm would generate less load (Table 1) and cover 64% of the terrace area.The two compositions overlap and build each other to create a gradual segmentation (land forming) of the terrace.For the smallest module, where the columns and beams are axially spaced 3.2 m apart, a wetland roof is proposed, which will be formed in the shape of a 'pond'.The area of this water element represents 4% of the terrace area.A bridge will cross the wetland, connecting the wooden and concrete walkways.Unwanted terrace layers such as those of the old green roof (the vegetation, substrate, and drainage system), paving stones, planters and gravel must be removed before the implementation of the new roof.The terrace needs to be insulated to meet all thermaltechnical requirements.Once the layers have been removed and the surface cleaned, the composition will be supplemented with thermal insulation based on a PIR board (due to its good thermal insulation properties with a smaller thickness) and a waterproofing layer resistant to root overgrowth.Subsequently, the frame will be installed into which the individual layers of the wetland roof are to be placed.At the same time, the green roof layers (protective, drainage, storage, and filtration layers) will be constructed, and the planters installed.The next step will be the filling of the substrate, shaping of the terrain, installation of the paths, and the actual planting of the vegetation.The last step will be the installation of the birdhouse and the insect hotel.

Conclusion
The greenIZOLA project is a vision for restoring vegetation in an industrial zone using green structures.It focuses on an office building with adjacent areas into which elements of green infrastructure will gradually be incorporated in such a quantity that the statics of the building is not compromised.The project is divided into individual phases, which have been gradually implemented since 2020.The fifth phase envisages the transformation of the building's terrace using elements that should ecologically enhance the environment, contribute to improving the climate, protect the layers of the roof structure, increase the biodiversity of the environment, and aesthetically beautify the building and its environment.The original green roof with a substrate thickness of 80 mm made up only 40% (70 m 2 ) of the entire terrace area.After the modifications, the vegetation area will make up 96% of the terrace area.As the green area increases, so does the accumulation of rainwater, slowing down the water runoff, increasing the cooling effect and the diversity of flora and fauna (insects and birds).Moreover, the terrace can serve as an example of incorporating a wetland roof into the design structure of biodiverse green roofs.At the same time, it can be used for experimental purposes to link research in engineering and natural science disciplines.This work was supported by a project run by Slovak Research and Development Agency APVV-18-0360 "Active hybrid infrastructure towards to a sponge city".

Fig. 1 .
Fig.1.Division of the project into phases for the green conversion of the building with the adjacent areas: 1 -Experimental green roof (green roofs and wetland roof); 2 -Existing shelter with three different compositions of a green roof; 3 -Carpor with a green roof; 4 -Extension of the western terrace on the 2 nd floor; 5 -Biodiverse green roof -park on the terrace; 6 -Existing shelter with a green roof; 7 -Green roof of the northern terrace on the 4 th floor; 8 -Green wall on the east and south side of the building; 9 -Biosolar roof.

Fig. 2 .
Fig. 2. View of the existing condition of the northern terrace on the second floor.

Fig. 3 .
Fig. 3.The floor plan of the northern terrace on the second floor -the division of the current and proposed states -Phase 5 of the project; (A-a green roof with an 80 mm thick substrate layer, B-part of the terrace finished with gravel; 1-a green roof with a 100-120 mm thick substrate layer, 2-green roof with a 150-180 thick substrate layer, 3-wetland roof, HI-insect hotel, BI-birdhouse).

Table 1 .
The area and load of the proposed compositions on the terrace.