New York's growing demand for green roofs (from The Guardian)

Central Park aside, New York City is better known for its dense concentration of towering buildings than its bountiful greenery. So it’s appropriate that the city is starting to use its ample supply of rooftop surfaces to make up for the lack of green space at ground level. Roof use has gradually increased in the city, with boutique hotels, art exhibitions, film screenings and even a women’s prison in Manhattan all getting in on the act.
But the recent rooftop trend has been more environmental in nature. Green roofs – a system of plants growing on waterproof membranes on top of buildings – are sprouting across New York City’s five boroughs. Given the potential to reduce greenhouse gases, increase energy efficiency and capture storm-water run-off, it’s easy to understand why.