At the first glance, it is not easy to understand the complete array of green roof’s environmental impacts. There are many attempts and comprehensive studies of this topic.
For example, Mihalakakou et al. (2023) did an extensive review of green roof contribution to energy conservation, carbon sequestration, mitigation of runoff pollutants, runoff control, urban noise reduction and life cycle assessment. He found that green roofs can reduce the cooling load by up to 70%, decrease the indoor temperature achieving an indoor air temperature reduction up to 15 °C, and provide a significant improvement of thermal comfort conditions. The environmental benefits of green roofs were focused on decreasing pollutants concentrations (e.g., PM2.5, PM10, O3, NO2), sequestering carbon and reducing urban noise.
Rasul et al. (2020) also did the life cycle assessment of green roofs, where the results indicate that green roofs impact about 3 times positively in the environment compared to non-green roofs. Most of the emissions reductions were found to be in the range of 35% to 83%. It was also found that environmental impacts of both extensive and intensive green roofs are comparable; however, intensive green roofs perform just slightly better.
Stepping aside from scientific papers, green roof industry should also reveal the environmental data by itself, for their product portfolio. Market data shows that some of the green roof suppliers disclose their environmental footprints with so called EPD – Environmental Product Declaration.
What is EPD?
What is of particular importance is, that it is made in standardised way of quantifying the environmental impact of a product or a system. EPD includes information on the environmental impact of acquiring the raw materials, energy consumption and efficiency, materials and chemical substances, emissions into air, soil and water, and waste generation. Product and company information is also included.
An EPD is created and verified in accordance with the International Standard ISO 14025, developed by the International Organization for Standardization (ISO). EPDs are based on a life-cycle assessment according to ISO 14040 and ISO 14044. It is an independently verified document that is based on the scientific principles of LCA (Life Cycle Assessment) and communicates the life-cycle environmental impact of the product.
Importance of EPDs for clients and for industry
EPDs in standardised form represent reliable data source for clients, as this approach allows to compare the products’ environmental impact between themselves. They contain: general information; product information; information about methodology used for life cycle assessment (LCA); LCA results; and analysis of LCA results.
In general information you will find the basic characteristics of the product itself, document expiry date and fact about the verification of the document. Information about product contains summary of product characteristics and performance. Information about LCA methodology include definition of functional unit (in this case 1 m2) and system boundaries (stages which are included in LCA).
System boundaries are very important part of the declaration, as they help you understand which are the stages, taken into account in LCA.
Urbanscape’s EPD includes all stages, namely:
The Product and construction process stage:Figure 1: The life cycle stages of construction products in general (Urbanscape EPD, 2022).
Reference service life (durability) must also be defined in EPD. Durability of a green roof can be with proper maintenance as long as the lifetime of the roof on which it is installed.
LCA results are presented in table format. In each column, the life cycle stages are described and their environmental impact disclosed. How much CO2 is emitted in declared unit life cycle stage, is shown by Global warning potential (GWP), shown as kg CO2 equivalent in functional unit. When you have all the stages, from cradle to grave analysed and disclosed, you can check how much CO2 is emitted during the specific stage.
At the end of the document, you can find the interpretation of the LCA. The Acidification Potential (AP), The Eutrophication Potential (EP), The Photochemical Ozone Creation Potential (POCP), The Abiotic Depletion Potential Minerals&metals (ADPmm) and The Abiotic Depletion Potential Fossil (ADPf) values during LCA stages are also described.
Green roof industry stakeholders should prepare and regularly update the EPDs for their products. Such approach reflects true dedication of the producer to minimize the environmental impact of their products and improve the production processes to meet the sustainability goals. Improved production processes are seen in, for example, decreased GWP values for their product portfolio. Small group (but good news is that it is growing) of companies, are providing specific EPD for their green roof products. It is also worth to mention, that EPD certificates can be used to obtain credits for building sustainability certifications, such as LEED or BREAM.
Transparent sustainability information reached by one click
By publishing EPDs, the transparent environmental information of green roof industry is disclosed. According to our current knowledge, Urbanscape green roof EPD is the only complete EPD in green roof industry, which includes all stages (from cradle to grave) in their LCA analysis.
Do you want to learn more? Check Knauf Insulation EPDs at Environmental Product Declarations (EPDs).
Literature
Rasul M.G. and Arutla R.K.L., 2020. Environmental impact assesment of green roofs using life cycle assesment. Energy reports, Vol. 6, Supplement 1. February 2020: 503-508.
Urbanscape EPD, 2022. https://www.knaufinsulation.com/knowledge-centre/environmental-product-declarations-epd