Analysis of Physical and Chemical Properties of Alternative Substrate Material for Sustainable Green Roofs

Abstract

Green roof of a building is partially or completely enfolded with vegetation and its associated components. It promotes the sustainability and comfort of buildings. This study determines the most suitable growing substrate by investigating organic wastes of Sawdust, Wood bark, Bio char, Coir, Compost and Base medium (fertilizer + potting mix) through comparing density, moisture content, drought resistance, thermal resistance, vegetation growth, pH, electric conductivity (EC) and nutrients. Unlike previous studies on green roof substrates, we have investigated chemical parameters and showed its importance on substrate selection. Unique mathematical concepts were used to find thermal conductivity and EC of specimens in our research. Preliminary study results shows that the most substrate composition includes 60% selected substrate and 40% base medium. Base medium (90:10) has highest bearing capacity to withstand external loads including vegetation and other imposed loads. Sawdust (60:40) exhibited consisted the least saturated unit weight, dry unit weight and the highest moisture content. In terms of drought resistance and vegetation growth, Bio char (60:40) was exceptional. Wood bark (60:40) exhibited the most convincing thermal resistance. The best characteristics in terms of pH, EC and nutrient content were exhibited by Sawdust (60:40), Coir (60:40) and Compost (60:40) correspondingly. Based on final ratings by considering all the experimental results, Coir (60:40) have emerged as the optimum growing medium in terms of physical and chemical properties. This experimental study results would provide a strong framework for construction industries to enhance sustainable green roof constructions with best practice in substrate selection.

Performance Analysis of Different Geotextile Materials in Extensive Roof Garden Designs

“…In addition, high EC (Electrical conductivity) has a negative effect on nutrient uptake such as pH and the productivity of the root zone environment where the plant grows. For this reason, the material that provides the lowest EC (Electrical conductivity) level among filtration materials is important in terms of creating a positive environment for plant growth in roof gardens (Sönmez, 2013;Kader et al, 2022). Therefore, in accordance with the results obtained from the research, it is recommended to use polypropylene fabric (F2) in extensive roof garden arrangements, as it has the lowest salinity value among the filtration materials.…”

“…Like other qualities, the pH level of the plant's root zone in the roof garden can change. However, it is suggested that the pH should be between 7.0 and 9.0, a range that allows the nutrient absorption of the plants used in roof gardens, and this should be stabilised to ensure the plants' health (Ampim et al, 2010;Kader et al, 2022). When the limit is exceeded, nutrients cannot be absorbed by plants and nutrient deficiency symptoms start being observed; root development, yield and plant quality are adversely affected (Sönmez, 2013;Ding et al, 2019).…”

Green roof substrates—A literature review

“…The main objective of this subtopic is to study regarding the growing mediums utilised in previous research studies and to know their corresponding mix proportions. Because the best fitting ration would not only enrich the vegetation with nutrients and water seepage (Young, 2014), but also prevent the substrate system from becoming a heavyweight component which is an essential requirement for the longevity of medium rise and high rise buildings (Ahmed and Alibaba, 2016;Khan and Asif, 2017;Mahmoodzadeh et al, 2019;Kader et al, 2021). Table 1 illustrates the details regarding the mix proportions and compositions used for substrate preparations in the past studies.…”

Feasibility study for estimating optimal substrate parameters for sustainable green roof in Sri Lanka

“…Green roof substrates are categorised into two main types: mineral substrates and organic substrates (Noya et al, 2017). In terms of mineral substrates, the naturally available topsoil, clay, pumice, sand, and gravel are used as substrates for green roofs due to their great ability to retain moisture (Kader, Jaufer, Shiromi, & Asmath, 2021). However, natural mineral-based growing mediums are hefty in weight, causing additional designs on the roof to maintain the structural stability of the structure (Ampim et al, 2010;Zejak et al, 2022).…”