The Role of Green Roofs in nZEB Constructions

In recent years, accelerated urbanization, polluting sources and industries have generated the phenomenon known as the Urban Heat Island (UHI), contributing to global warming. This heat island represents an increase in temperatures in densely populated urban areas compared to the surrounding countryside. The negative impact of UHI can be quantified for proper facility design and energy consumption assessment of buildings, and requires effective interventions to mitigate and reduce environmental and human health consequences.

As the UHI leads to an increase in the energy consumption of buildings, especially during the summer, the control of indoor temperatures becomes crucial. However, the external environment is difficult to manage, and solutions are oriented towards interventions that reduce the effects of pollution and establish comfortable climatic conditions. High temperatures in the urban environment, especially during summer, can have significant consequences on health and daily life, and highlight the need to take appropriate measures.

Decarbonisation of the energy sector is a priority in achieving climate and energy objectives. The Energy Performance of Buildings Directive states that all new buildings in Europe must have a very high energy performance, where the energy requirement is almost zero (nZEB) from 2021. This is part of the European policies that promote energy efficiency and renewable sources to achieve a climate-neutral continent by 2050, according to the European Green Deal.

The construction sector has a significant share of total energy consumption and carbon emissions in Europe, being responsible for 40% of these. Improving the energy performance of buildings is an important objective of the European Union, staged for 2020 and 2030, aiming to reduce energy consumption by 20%, reduce carbon emissions by 20%, and increase the use of renewable energy by 20%. The 2030 targets aim to reduce domestic carbon emissions by 40% and decrease energy consumption by 25%.

European legislation on the energy performance of buildings has been strengthened by reforming the Renewable Energy Directive. These normative acts required member states to ensure that all new buildings become nZEB by the end of 2020. In the same context, the European Commission proposes that at least 27% of the EU’s energy
consumption should come from renewable sources by 2030.

The Role of Green Roofs in nZEB Constructions

In accordance with European regulations, in Romania, Law no. 372/2005 on the energy performance of buildings stipulates that new constructions must reach nearly zero levels of energy consumption from conventional sources by the end of 2020. For new buildings owned/administered by public authorities, approved after 31 December 2018, the same requirement will be applied. This regulation highlights Romania’s commitment to contribute to the European objectives of energy efficiency and reduction of carbon emissions.

The construction of nZEB buildings, integrated with renewable technologies, plays a key role in achieving European energy efficiency and carbon reduction targets. They not only meet legislative requirements, but also contribute significantly to the creation of a healthy and sustainable urban environment. Implementing these building standards and practices is vital to ensuring a cleaner and healthier future for future generations.

Benefits Of Green Roofs Installed On nZEB Buildings

Green roofs have become an innovative and ecological solution in the context of nearly zero energy consumption (nZEB) buildings. This type of green infrastructure brings many benefits, influencing both building performance and urban impact. 

Regarding the constructive model of green roofs, they can be classified into different categories: extensive, semi-intensive and intensive, depending on the substrate depth and the type of vegetation used. 

Extensive roofs adapt to different contexts and requirements, being light structures, which are suitable for buildings with lower loads. Intensive and semi-intensive roofs have a higher substrate height, and require structures with a higher load-bearing capacity to support the weights imposed by the layers and vegetation.

At construction`s level, green roofs bring significant energy savings, reduce sound transmission in buildings, contribute to gray water treatment and increase the lifespan of the roof structure. Last but not least, green roofs can improve the performance of photovoltaic panels, thus providing a synergistic approach between green solutions.

At the urban level, green roofs and walls demonstrate impressive potential in supporting ecosystems. By mitigating the Urban Heat Island Effect, managing water systems, reducing noise and improving air quality, these developments contribute significantly to creating a sustainable and healthy urban environment. Their large-scale implementation can bring additional benefits, such as improving aesthetics, recreational use of public spaces and promoting biodiversity.

Thermal Insulation

Green roofs provide additional thermal insulation, thus reducing the energy need for heating and cooling. The substrate and vegetation act as a natural thermal barrier, helping to regulate indoor temperatures and increasing energy efficiency of buildings. Studies and research in the field show that green roofs represent a flexible controller of the penetration of solar radiation and wind into buildings, having a significant impact on energy efficiency and thermal comfort.

Green roofs provide a 25% to 60% reduction in heat transfer compared to conventional roofs.

Temperature Reduction

Green roof`s vegetation influences the microclimate of the surrounding area, having a significant impact on surface temperatures. The evapotranspiration generated by the plants contributes to the cooling of the environment, thus the temperature in the buildings decreases, regardless of the intense solar radiation during the summer. The cooling effect of vegetation on green roofs helps reduce the Urban Heat Island Effect. This is achieved by absorbing and blocking solar radiation, evapotranspiration and reflecting sunlight. The cooling effect is manifested by a reduced heat transfer between the outside and the inside of the building.

By using green roofs, the maximum surface temperature during the day, in summer, can be reduced by 15 - 45 °C, and the maximum air temperature by up to 5 °C.

Contribution to Gray Water Treatment

In addition to thermal benefits, green roofs play an essential role in stormwater management. They absorb and retain rainwater, have a major role in preventing floods, soil erosion and overloading of urban sewage systems during heavy rains. A green roof, in general, can absorb and retain between 50% and 90% of the precipitation volume. The water absorbed by the vegetation and substrate goes through a natural filtration process. Plant roots and substrate retain particles of impurities, such as air polluants or other harmful substances in the air.

Thus, the water discharged from the green roof system is cleaner, helping to improve the overall water quality. 

The water captured by the green roofs can be used for various non-potable purposes, the gray water can be used to irrigate the intensive roofs, thereby they are completely purified, so clean water is discharged from the roof.

Extended Waterproofing Life

The green roof structure acts as a protective layer, providing a barrier against external elements such as ultraviolet radiation, rain, heat and cold. This aspect is particularly important for waterproofing membranes, which can be sensitive to external factors and, in the absence of a protective layer, can suffer premature degradation. Green roofs are a valuable investment in construction, extending 2-3 times the lifespan of waterproofing membranes. They can reduce the costs associated with frequent roof renovations and help achieve sustainability goals in construction.

Contribution to Obtaining Certificates

In some cases incentives, certifications or credits are offered for sustainable building practices. Thereby, the implementation of green roofs can bring additional benefits and recognition within the regulatory and certification programs for sustainable construction, for example it can contribute to the achievement of BREEM and LEED points. A biosolar roof, which combines green features with solar energy, can maximize these benefits.

In addition to the benefits added to the functionality of the building, green roofs also have a great aesthetic value. They contribute to the visual appeal of the building and promote biodiversity. Rooftop vegetation creates a harmonious and environmentally friendly appearance, being particularly attractive in urban environments. According to studies, the use of green roofs can make the property more attractive to potential buyers and contribute to an increase in its value by 6 – 15%.

In addition, green roofs contribute to improving air quality by capturing polluting particles and CO from atmophere, an essential aspect in urban areas affected by intense pollution. A green roof of 93 m2 has the capacity to remove 18 kilograms of polluting particles from the air, equivalent to the emissions generated by 15 cars driven for a year. These roofs also act as sound insulators, reducing external noise levels and helping to create a quieter and more comfortable indoor environment.

The Advantages of the Biosolar System Compared to PV Modules Installed on Conventional Roofs

In the era of ever-evolving solar technology, the issue of space and energy efficiency is becoming increasingly relevant in the context of constructions. Building a house with a south-facing attic can have difficulties in getting the right angle for the solar panels or can involve significant costs due to the need for an additional wall. The classic installation of photovoltaic systems faces the problem of insufficient space on traditional roofs, unable to accommodate the required number of panels to meet the energy requirements of the building. 

An effective approach consists in developing cost-effective strategies for maximizing energy efficiency and the use of renewable sources. If the legislation requires the installation of solar panels on buildings, the optimal choice becomes a terrace-type green roof with a Biosolar system, an innovative solution that combines the production of solar energy with the benefits offered by a green roof. This innovation makes a significant contribution to the overall energy efficiency of the building, acting simultaneously as an electrical energy generator and thermal insulation.

The intelligent integration of solar technologies and green roofs into a single system brings multiple benefits, such as increased energy efficiency, maximum use of available space, reduced building maintenance costs and positive environmental impact. Current researches are focusing on optimizing photovoltaic systems by integrating them into green roofs.

An essential aspect of the system is due to the evapotranspiration of the plants, which exerts a cooling effect on the environment, with an implicit positive impact on the photovoltaic panels. Excess heat can negatively affect the efficiency of the panels, but the cooling generated by the vegetation contributes to maintaining an optimal temperature for operation and improving the performance of the photovoltaic system. 

According to studies, using the system can lead to up to a 15% increase in electricity production compared to conventional roofs. Surface temperatures on green roofs are significantly lower by up to 45 degrees compared to classic dark-colored waterproofing, which translates into additional electricity production. Depending on factors such as plant types, roof performance and climate conditions, biosolar green roofs can contribute up to 8.3% of a building’s total energy consumption. Photovoltaic panels also provide shade for vegetation, improve drought resistance and contribute to a positive impact on biodiversity. As a result, the biosolar system is established as a viable and efficient solution, compared to traditional roofs equipped with photovoltaic panels. 

This system can be implemented on both new and renovated buildings, covering the entire roof surface. It is installed without penetration of the waterproofing, ballasted by the weight of the substrate and the vegetation. The positive effects of this combination of photovoltaic panels and vegetation include an improvement in energy efficiency, better filtration of rainwater, effective thermal insulation and a significant increase in biodiversity.

Studies On Enhanced Roof Efficiency Green On nZEB Buildings

Recent studies demonstrate that green roof systems are a viable solution for saving energy and reducing the urban heat island phenomenon. In order to obtain measurable results, a green roof was monitored on a building in Aprilia, near Rome, Italy. Natural turf was installed on one side of the roof, while the other side remained in its original state with a conventional roof. In the autumn season, measurements show that the green roof maintains remarkable thermal stability. 

External and internal surface temperatures of the green roof are very well differentiated, without overlapping. The conventional tiled roof, on the other hand, exhibits high thermal fluctuations, suggesting low thermal inertia. By analyzing the outside temperatures of the two types of roof and the outside air temperature, it is observed that the temperatures of the conventional roof oscillate in accordance with the air temperature, unlike the green roof, which does not show this correlation.

Temperature fluctuations measured between 20/09/18 and 04/10/18
Temperature fluctuations measured between 20/09/18 and 04/10/18
In conclusion, the experimental investigation of the green roof system revealed significant benefits. The system exhibited higher thermal inertia, lower thermal transmission and more favorable indoor conditions. The difference in thermal resistance between the green
roof and the classic one was about 50%.

The green roof proves to be an effective solution for improving the energy performance of nZEB buildings. This passive system not only optimizes thermal inertia, but also contributes to reducing energy consumption and improving interior comfort. In addition, in urbanized areas, it can help combat the Urban Heat Island (UHI) Effect and capture air pollutants. Therefore, the positive impact of green roofs becomes obvious, both from an economic perspective and from the the environmental perspective.

Although green roofs may involve higher initial costs, the long-term savings in energy consumption, reduced environmental impact and improved building performance can make them a valuable component of nZEB strategies. Green roofs are not only a viable option for buildings, but also an effective urban solution, having a positive impact on the environment and quality of life. By implementing these systems, the way to a sustainable and environmentally friendly built future is opened.

Be part of the sustainable future of cities, choose green innovation for a healthier environment!

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