Chicago’s City Hall. Image: wikimedia commons.

Spring downpours may evoke the expression: “raining cats and dogs.” In days of thatched roofs, domestic animals burrowed into the substrate, jumping forth during vernal storms. Green roofs (and walls) are making a comeback. Insulating, sound absorbing, green roofs soak up 70% of rainwater, reducing local flooding. Green roofs feature recycled materials. The Roman aqueducts, and roads, as reported by Vitruvius, were 1 part chalk + 2 parts sand (preferably local volcanic pozzolanic) + 20% water. Chicago, USA; Paris, France; Toronto, Canada passed laws requiring new construction include solar or green roofs. Chicago estimated energy savings of $100,000,000 annually, if all its urban roofs were green. Environmental benefits await: while a shady lawn’s summer surface temperature averages 28C, non-green urban roofs measure 52C (125.6 Farhrenheit). Green roofs, especially in cities, may help fulfill the promise of the COP21 agreement.

Building the World Blog by Kathleen Lusk Brooke and Zoe G Quinn is licensed under a Creative Commons Attribution-NonCommercial-NoDerivs 3.0 Unported License