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Abstract
Green roofs, also known as vegetated roofs or roof gardens, use soil and vegetation to retain and detain precipitation on impervious roof tops. While runoff reduction is an accepted benefit of traditional green roofs, not all roofs are amenable to this design. Newly developed modular designs are more versatile, but their stormwater remediation ability requires assessment. This study quantifies water retention and detention by modular green roof blocks. Twelve blocks were monitored for one year using four repetitions of three treatments (reference, non-vegetated, and vegetated). Stormwater retention and detention was compared within and among treatments and to a traditional extensive green roof located adjacently. The modular green roof blocks retained more than 43% of the total precipitation and reduced runoff 60% when compared to the reference treatment. Little difference was observed between the vegetated and non-vegetated treatments suggesting that the sedum vegetation used in this study was insignificant in providing retention and detention. Comparisons between the modular green roof blocks and the traditional green roof showed a greater retention in the traditional green roof.