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Stores, rooftops and parking lots: urban spaces to be "greened"

Current trends in urban design include green roofs on buildings and highly visited places, such as shopping centers. One of the experiences had a supermarket in Florence that replaced the ventilation system with a sort of greenhouse for air exchange

by Pietro Piccarolo
July - August - September 2022 | Back

The ongoing ecological transition process has raised awareness of the fact that a "green" city is the answer to a social demand. As a matter of fact, citizens, oppressed by overbuilding, environmental and noise pollution, are demanding that cities become places with a good quality of life. Urban greenery, via the ecosystem services it is able to provide, is becoming essential for making cities truly sustainable also from the point of view of the citizens' health and well-being. Indeed, green spaces are key climate regulators capable of reducing the effect of "heat islands" and air pollution, as well as limiting the intensity of weather events and promoting biodiversity. In addition, there is an increase in the aesthetic landscape and economic value of the areas and buildings concerned and the possibility offered to people to spend their leisure time in places where nature prevails over concrete.

For greenery to perform its functions to the fullest, it must be adequately designed, where the choice of plant composition also considers its sustainable maintenance. Therefore, the role of the public agency is crucial but cannot be separated from the involvement of private individuals. This article aims to emphasize three types of urban greenery for which the contribution of private individuals can be highly significant. This refers to "commercial" green and " greening" of roofs and parking lots.


Green in stores

Shop owners should become aware that adding plants in front of and inside the store improves the evaluation with which the business is perceived, increases its attractiveness, and enhances the perception of the quality of its offerings. Therefore, having plants in place is not only a way to increase the customer base but also a way to contribute to the city's green space and the ecosystem services it can provide to customers and the shopkeepers themselves.

In a major supermarket in Florence, for example, an experiment was made to eliminate the energy-intensive mechanical air ventilation system by inserting a greenhouse that, through plants, implements botanical air purification. To this end, plants with a large leaf area were carefully chosen and arranged in multiple layers to form an effective filter barrier. Through this system, the air inside the supermarket is not replaced but recycled. In addition to the energy savings, the benefits to customers and employees in terms of working conditions and increased well-being should be considered.


Vegetalized roofs

The benefits that plant-covered roofs bring to the city are of great interest as they locally reduce the effects of "heat islands," promote atmospheric cooling and manage rainwater. They also reduce the building's energy consumption for heating and cooling. Implementing this solution requires, first of all, the construction of a waterproof roof covering, on which a vegetation system is to be built consisting of: a drainage layer, a filter layer, a substrate, and a vegetation cover. According to the substrate's structure and thickness, the roof type can be: extensive, semi-intensive, and intensive.


Extensive roof

Substrate thickness is between 4 and 12 cm and consists of 10 percent organic matter and 15 percent fine soil. For thickness below 8 cm, the choice of plant species goes toward xerophytic plants, such as the various sedum species, which are hardy, undemanding and have good particulate absorption capacity. Above 8 cm, the plant composition can be integrated with bluebells, fescues, irises, etc. The maximum load does not exceed 180 kg/m2.


Semi-intensive roof

Substrate thickness ranges from 12 cm to 30 cm, with 10 percent organic matter and 20 percent fine soil. For plant composition, turf grasses, some varieties of roses, and other similar essences are added to the species mentioned before. The maximum load is contained within 350 kg/m2.


Intensive roofing

Its thickness exceeds 30 cm, and the composition is that of garden planting substrates. As for vegetation, when the thickness of the substrate exceeds 1 meter, in addition to the herbaceous essences mentioned before, shrubs and tree plants can be inserted. Loads of even more than 500 kg/m2 are reached. Grassing can be implemented with different techniques. It is possible to use herbaceous cuttings to be inserted into the substrate, seedlings grown in soil cubes, or turf transplant in rolls or plates pre-cultivated in particular substrates. The irrigation system is necessary for the Mediterranean area and is recommended in other areas, keeping in mind, however, that the cooling function is still improved with irrigation. To determine the irrigation dose and frequency, it is essential to know the water retention capacity of the substrate. Irrigation intervention should be linked by sensors measuring substrate moisture and evapotranspiration to the vegetation's water needs, avoiding predefined doses and intervals. The irrigation technique must ensure uniform coverage and can be implemented: by sprinkling, drip-drip, and sub-irrigation.


Vegetalized parking lots

In addition to the better aesthetic effect, vegetated parking lots increase the permeable surface area of the city soil, reduce the albedo effect, that is, the reflectivity of solar radiation, and mitigate the impact of heat islands. Before implementing this solution, it is crucial to know both the bearing capacity and the permeability of the soil. Specifically, the permeability coefficient should not be less than 6-10 m/s.

The most common solutions are honeycombed plastic or concrete structures resting on a support layer consisting of a mixture of soil, stones, or other nature. The thickness varies from 20 to 50 cm and is related to the type of use, particularly the weight of the types of vehicles to be stationed there. The honeycombed slabs are filled with a pre-seeded layer of soil and crushed stone, either by resorting to mechanical seeding and even hydroseeding or transplanting turf sod.

The choice of seed should be directed toward hardy species with highly dense root systems capable of rapid regeneration.


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