Roof top gardens as a means to use recycled waste and A/C condensate and reduce temperature variation in buildings

It is no secret to anyone living in Beirut or a similar modern city in a semi-arid tropical country in the summer that their home has become a concrete forest and an urban heat island. Old wood or stone houses and their gardens have been replaced by concrete towers and parking lots, in the name of development. The result is searing summer nights, a drastic loss of insect and avian biodiversity, and a large increase in energy usage for interior climate control. These problems are experienced in rapidly developing urban centers worldwide. Moreover, cities worldwide are struggling with waste disposal. Roof gardens can help solve both problems. They also can have a non-proportional effect on energy flux, especially if buildings are high and closely packed. The present work assessed the potential benefits of a roof garden on a bare flat roof in Beirut. The possibility of using recycled material as garden substrate was assessed; the effect of roof gardens on temperature variations below the roof was evaluated; and finally an assessment of whether enough water can be collected from air conditioner condensate to support a roof garden and whether the water is suitable for agriculture was performed. Results strongly indicate that post factum construction of rooftop gardens positively affects urban area and building environment in a variety of ways.