Assessment of recycled or locally available materials as green roof substrates

Importance of green roofs are growing due to their several benefits in urban areas. To provide a sustainable green roof system and reduce the negative environmental effects of green roof construction, recycled or locally available materials plays a crucial role. A study was conducted to evaluate the potential of four recycled materials (crushed concrete, crushed bricks, sawdust, and municipal waste compost) and five locally available materials in Istanbul (lava rock, pumice, zeolite, perlite and sheep manure) as green roof substrates over one year period. Twelve-substrate mixture were prepared at the site by mixing six inorganic mixtures (crushed concrete, crushed bricks, lava rock, pumice, zeolite, perlite) with two organic amendments (municipal waste compost and sawdust-sheep manure mixture) with a ratio of 8:2 by volume. Specific measurements such as plant growth index, chlorophyll fluorescence, plant coverage ratio and survival of plant taxa were performed on five native plant species, Allium schoenoprasum, Helichrysum italicum, Sedum lydium, Stachys thirkei and Thymus vulgaris. At the end of the 58 week study period, pumice and perlite-based substrates amended with municipal compost outperformed remaining substrate mixtures in terms of plant growth, plant stress, chemical and physical properties. Moreover, performance of substrate mixtures consist of concrete, crushed bricks, lava rock, zeolite amended with sawdust and manure were adequate in some cases, which could be preferred as a green roof substrate by admitting suggestions offered in the study. •Evaluated recycled or locally available materials on plant growth.•Recycled or locally available materials could be used a substitute for commercial substrates in green roof design by admitting suggestions offered in the study.•Substrates containing perlite and lava rock strongly affected by ambient temperature fluctuations resulted with plant mortality on Thymus and Helichrysum species.•Particle size distribution, silt-clay content and content of the substrate mixtures had a significant effect on volumetric moisture content (VMC) values.•During drought periods, the coarser substrates dried out faster due to limited water availability in the substrates, which caused a significant decline on Fv/fm levels.