There are thousands of green roof benefit claims widely available out there. In this enormous amount of different information, facts and figures, how to distinguish what is green washing and which claims are based on actual evidences, time series measurements and data analysis?
Green roofs are….
Saving environment, mitigating heat island effect, lowering housing energy bills, mitigating noise, contributing to biodiversity, lowering rooftop surface temperature, increasing solar panel’s’ efficiency, capturing stormwater, and many many more. Yes, indeed green roofs are doing that.
But there are always two sides of a coin. Green roofs have in general positive environmental impact during their operation life on a roof. Out of curiosity, how much do we know about green roof environmental impact during their whole life cycle, from resourcing, production and end of life stages? It appears that not so much.
Transparency is the key
Green roofs have the environmental impact during the whole life cycle - from cradle to grave. Do we know it? The answer to these question lies in Life Cycle Assessment (LCA) analysis.
Figure 1: Green roof LCA features in scientific articles’ review (Piccinini Scolaro and Ghishi, 2022).
As Ferreira Alves (2015) explains in his case study for two green roofs, the results of the Life Cycle Impact Assessment show that the global warming potential (GWP 100 years) of the extensive green roof has a positive impact, explained by the CO2 sequestration produced by the vegetation layer along their lifetime. Extensive roofs are sustainable products in the long term, but he emphasised that more research is needed in the area of the constituent materials of their functional layers (shape layer, waterproofing membrane, insulation and drainage layer), in order to improve environmental performance. There are different approaches towards LCA. Shafique et al (2020), used material extraction, transportation, construction, operation/maintenance, and disposal phases in their LCA analysis. Many authors call for more uniform scientific approach in green roof LCA framework.
What does green roof industry reveal?
Shafique (2020) studied the LCA approach evolution in green roof industry, where first studies were done more than 15 years ago and continue nowadays by different scientists, but much less by industry itself:
For the complete transparency, green roof industry stakeholders should
- monitor and
- disclose in uniform format
the environmental impacts of their green roofs from cradle to grave: from raw materials extraction and processing, manufacturing, installation, use stage (with all operational steps during the shell life of the green roof such as maintenance, repair, replacement, water use), deconstruction, waste processing, disposal, packaging and all the transport routes during the whole life cycle and for all green roof system layers.
Green roof industry’s customer should be able to compare these data in uniform format, which would enable complete transparency of the available products on the market on one hand and well-informed buying decisions on the other hand. Far from reality? Yes.
Where to search for such data and how to compare “apples to apples”?
Firstly, customers should check with the producer if he has done the complete LCA – from cradle to grave stages. These findings should be declared in EPD. EPD is environmental product data sheet, which will be more in details described in one of our next blogs.
Figure 2: Urbanscape EPD, 2022.
Existence of products’ EPD reveals transparency in environmental footprint of analysed product. When such EPD is compared to competitors’ EPD, one can decide, which of compared products has lesser environmental impact. To ease this process for our clients, Urbanscape EPD was compared to competitors’ EPD with so called Eco-index score. Unfortunately, only one comparison was made as, to our knowledge, only two EPDs (Urbanscape EPD included) are publicly available currently.
Eco-index score is a single score, represented by emissions documented in EPD. Without such tool, the EPD comparison is not relevant due to, for example different units of pollutants, Comparison is enabled with developed Eco-index method, which incorporates scientifically proven methodologies (such as shadow pricing methodology by CE Delft, used also by European Commission among others).
Food for thought
Green roofs are one of nature-based solutions which helps sustain our environment in better condition and contribute to human’s well-being. When owner decides to put the green roof in the rooftop, he does that for many reasons, prevailing philanthropic, environmental consciousness to pure economic reasons. No matter the reason, investors must be fully informed before making the decision, where the quality and uniformity of data is the key. When they want to understand the environmental impact of the investment, the transparent data should be in their reach. It is our - green roof industry - responsibility to reveal what we are offering to the market, without green washing.
Ferreira Alves, A.L., 2015. Life Cycle Assesment of extensive green roofs in Lisbon. DECivil, Instituto Superior Técnico, Lisbon University, Lisbon, Portugal.
Piccinini Scolaro T. and Ghishi E., 2022. Life Cycle Assesment of green roofs: A literature review of layers materials and purposes. Science of The Total Environment, volume 829, July 2022.
Shafique M. et al., 2020. An overview of life cycle assessment of green roofs. Journal of Cleaner Production, volume 250, March 2020.