Green roofs from locally-available materials

Vegetated (green) roofs may be found in metropolitan areas where ordinances and incentives to encourage their installation have been implemented, and to a lesser degree in small municipalities and rural areas where access to materials and green roof technology is limited. To encourage building owners in rural areas and smaller municipalities to install green roofs, locally available materials and two modular systems were trialed on a demonstration site for efficacy in a green roof system. Two media substrates were trialed: one using locally available trap rock (hadite) and the other using reclaimed lava rock (red) in place of the trap rock (80% of the media). In addition, sand (12.5%), peat moss (5%), and compost (2.5%) were added to each mix. Two species of sedum (S. reflexum, S. spurium) were installed on the roof in one of two containers: specially-designed landscape fabric bags or plastic flats such as those used for bedding plant production. Media substrates and containers were combined in four possible iterations. They were arranged in a completely randomized design on a rubber-membrane covered roof having a 2/12 pitch (16.67% slope). Plant growth was evaluated a year after plants were established on the roof, and at the end of the second growing season. Results indicated that plants grew better in lava rock-based media than trap rock. Plants also grew better in flats than landscape fabric bags. Whereas some treatments had a score of zero, indicating no plants had survived, others had scores as high as ten, on a scale of 1-10. In spite of severe drought and above-normal temperatures the first year (2012), plants looked better overall in September of that year than they had in March.