Green Roofs in Infill Development to Improve the Environmental Safety of Urban Areas

Introduction. Modern cities are actively integrating new environmental solutions into their infrastructure, and green roofs have already become a traditional element of urban planning [1]. Recent studies have demonstrated that these structures significantly contribute to the efficient use of urban space and significantly improve the environment [2][3]. The effectiveness of plant coatings in neutralizing pollutants, including PM0.5-PM10 has been confirmed by numerous studies [4][5]. Today, green roofs are not considered as an innovative concept, but rather as a crucial part of strategies to improve urban ecosystems. Experts and the public are increasingly recognizing their contribution to enhancing the quality of life for citizens and restoring natural balance in urban areas [6].

Studies have shown that residential buildings significantly worsen the quality of air in cities, releasing harmful PM0.5-PM10 particles, which negatively affect the health of residents [7]. Therefore, architects and developers should consider green roofs as a standard element of construction projects [8]. The introduction of such eco-friendly solutions into everyday practice is becoming a key factor in ensuring the environmental sustainability and safety of modern urban planning [9].

The limited availability of natural resources in cramped urban spaces requires their rational use and functional expansion, which is especially important in the case of residential development and reconstruction of outdated buildings [10]. The strategy of replenishing such dwindling resources is the introduction of environmentally friendly and economically cost-effective architectural concepts, including green roofs [11]. These solutions minimize dust pollution in residential areas, have a beneficial effect on the quality of life of urban residents, and contribute to more efficient environmental management [12].

In an urban environment where space is limited, the transformation of standard roofing structures into ecological oases seems to be a perfect solution for the restoration of natural cover. This is particularly true when there are no other land use options available. A green roof is a multi-level structure that sits on the top of buildings [13]. It includes a base and a variety of intermediate elements, from waterproofing barriers to vegetation cover. All these layers function as a single mechanism that ensures the vital activity of flora on the roof and effectively replenishes the green areas lost during the construction process. The implementation of such projects requires detailed design and analysis of weight characteristics to ensure the reliability and stability of these innovative systems.

The research focus in the area of green roof systems is primarily on their ability to clean the air of such pollutants as SO₂, O₃, NO₂ and PM10 [14][15]. Vegetation on roofs, like other urban landscaping elements, shows significant potential in reducing atmospheric pollution and harmful emissions by up to 35–100%. This has been demonstrated through research, and these environmental benefits have led to an increasing interest in green roofs worldwide.

The aim of this research is to evaluate the effectiveness of green roofs in reducing the spread of dust in urban environments, which is particularly important for areas with active infill development. To accomplish this goal, we have solved the task of identifying vegetation types that effectively collect dust, and developed designs for green roof systems that were suitable for installation in residential areas. Such environmental solutions contribute to the overall modernization of the construction industry, making it safer for the environment and more comfortable for residents.

Materials and Methods. The choice of an optimal location plays a key role in maximizing the benefits of green roof structures in the fight against PM2.5 and PM10 pollutants, given the difficulties with their installation. For Russian cities, there are specific parameters for determining the priority areas for the installation of these environmental structures. One of the most important factors is the location in a certain climatic zone according to the zoning scheme (Fig. 1) [16]. It is the correct location of green roofs that determines their effectiveness in reducing the concentration of harmful particles in the atmosphere.

Modern urban trends require a systematic approach to creating eco-friendly spaces in an urban environment. This task can be solved by developing affordable, cost-effective and technologically uncomplicated solutions. The criteria for implementation include location in urban centers with a population of more than 250,000 people, as well as the prerequisite that green areas make up at least 40% of the total area of the block [17].

During the construction of the Krasny Aksai residential complex in Rostov-on-Don, herbaceous plants of six varieties typical of the Rostov region were planted in March 2020 in the construction area and outside the site (Fig. 2). From May to September, during the construction of the monolithic frame of the building and the stone-installation works, 10 air samples were taken twice a week for 120 minutes at three control points according to the standard RD 52.04.893–2020¹ method — at the border of the construction site at 117 b, Beregovaya St., b. 5 (point A in Fig. 2), above the vegetation zone (point B in Fig. 2) and at a distance of 10 meters from the green zone, in the residential area of the Krasny Aksai residential complex (point C in Fig. 2). During the entire observation period, atmospheric parameters fluctuated: the air warmed up from +14 to +25°C, the wind reached 3–5 meters per second, and the relative humidity was from 30 up to 60%.

Each plant species planted in the area of the site occupied an area of six square meters, forming a total experimental area of 36 square meters. All the selected plants had a high dust absorption capacity, which was a key criterion in their selection for this study (Fig. 3) [18][19].

The methodology for determining the amount of dust deposited on plants involved taking 50 measurements twice a week in the morning. Dust particles were collected from the surface of plant leaves using a brush. The process took place during the period of active construction of a multi-storey residential building, that is, from May to September 2020. The collected material was carefully transferred into a pre-weighed container for further evaporation and weighing. After collecting samples from each plant species, laboratory treatment was performed: the liquid was evaporated and the sediment was dried until the mass stabilized. Using these recorded indicators, we were able to calculate the specific dust concentration — the number of milligrams of dust collected per square centimeter of plant leaf surface. The results of particle deposition on the leaves of the studied plants can be seen in Figure 4.

Air sampling to determine dust concentration in it was carried out using an electric aspirator PU-3E/12, which was tested, and filters made of PVC fibers AFA-VP10. Preliminary tests of this measuring equipment in a wind tunnel showed that the measurement error during a one-time experiment did not exceed 12%, which met the requirements of RD 52.04.893-2020.

Results. The analysis of measurements showed that in conditions of prevailing easterly wind (3–5 m/s) and an air humidity of 30–60% during the period of work, the planted vegetation significantly affected the air quality. Above the landscaped area, there was a decrease in the concentration of PM10 dust particles from construction work from an average of 10 (humidity — 30–35%) to 20% (humidity — 35–60%), and at a distance of 10 meters from the vegetation cover, compared with the adjacent construction area, from an average of 15 (humidity — 30–35%) up to 30% (humidity — 35–60%).

Measurements of the amount of dust deposition during the growing season (May–September) revealed the following dynamics: if at the beginning of the season (May–June) the amount of dust deposition on plants was a maximum of 0.42 mg/cm², then at the height of the warm season (July–September) it reached 1.81 mg/cm². The dynamics of changes in the amount of dust deposition on plants was explained by the fact that during the measurement period, plants grew at the beginning of the growing season, then the area of vegetation increased, but at the same time, the dust deposition formed on the leaves could be blown into the air by the wind at a speed of 3.5 m/s and higher. In the period from July to September, the vegetation surface area was already at its maximum. The process of active dust deposition was also influenced by the fact that dew formed on plants in the first half of the day, and the volume of green mass of plants, which allowed dust deposits to accumulate on the leaves, prevented external sources of exposure (wind, precipitation) from sweeping the dust deposits onto the ground or into the air. Figure 5 shows the dynamics of changes in the PM10 concentration during the study period at three control points for measurements (construction site, vegetation area, residential area).

To achieve the aim of this research, the authors have developed innovative, resource-efficient and practical green roof designs that can be incorporated into the planning stage of residential developments. These designs can easily serve as a tool for reducing the negative impact of dust emissions during construction, whether it is the construction of new buildings or the renovation of the existing structures for various purposes.

The first mobile green roof structure was developed with the possibility of its dismantling for the winter period. Patent No. 191863U1 was registered for this type of roof [20]. The structural elements of such a roof were a combination of reinforced concrete slab, durable anti-rot roofing felt, adjustable Forest Style supports made of high-strength propylene (with the possibility of building up due to an additional nozzle of 60 mm), as well as Ondulin double-layer asphalt concrete coating. Figure 6 provides the structural scheme of the green roof and the implementation of this structure at the facility after reconstruction in Rostov-on-Don.

The second type of structure is intended for residential buildings, winter gardens and terraces. This system is characterized by simple dwsign, cost-effectiveness, high thermal insulation, and moisture protection. Patent No. 163334U1 [21] was registered for the utility model. The vegetation layer is planted in the final stage of the project. It is placed along the perimeter of the green areas of the structure. The installation of this type of roof involves the use of two types of coatings: one for the side section, which allows for year-round use of the green roof, and the other for the central area, where a swimming pool or café can be located, for example.

Figure 7 shows the developed design of the second type of green roof, which consists of a reinforced concrete floor slab, filter and vegetation layers. Ondulin is used as a protective element. The structure is additionally equipped with a layer of anchors in the ground. The implementation of this design solution at an urban development facility is also presented.

The cost of these green roof structures starts from 4,200 rubles per square meter. Financial calculations show that with long-term operation (up to 40 years), traditional and green roofs have approximately the same cost. At the same time, investments in the installation of green roof systems for the League of Nations business center amounted to only 1.3% of the total reconstruction budget. In the case of the Zhemchuzhina Dona multi-apartment high-rise residential complex, the share of costs for the development of design solutions, installation and landscaping of the roof amounted to 4% of the total construction costs of the facility.

Discussion and Conclusion. The research conducted by the authors proves that the creation of vegetation cover is a fairly effective barrier to the spread of dust pollution from infill construction. The efficiency of dust collection can reach an average of 10 to 20%, depending on the air humidity level. At the same time, it is important to choose the right plants for the green roof and arrange it well in order to maximize the effect of dust suppression, which will significantly increase the environmental safety of residential areas in residential buildings. The two types of constructive green roof solutions developed by the authors, which are applicable for the reconstruction of buildings and the construction of new facilities, make it possible to create a comprehensive protection of the urban area from one of the most harmful sources of dust emissions in the urban environment — the construction site. Although the introduction of such technologies requires additional financial investments, they are offset by a decrease in the incidence of workers from harmful effects of dust by about 15%. This leads to a corresponding reduction in the cost of construction work and labor savings, while providing a higher level of protection for both workers on the construction site and residents of nearby areas.