Cooling Heat Islands
January 24, 2011 § Leave a comment
Dark, non-reflective hardscapes in the city – such as streets, parking lots, building roofs, sidewalks – are known to create heat islands, areas that have an artificially elevated ambient temperature when compared with temperatures in more sustainable environments. We southern Californians enjoy our sunshine, but this type of artificial, urban heat is quite harmful, and can have immediate and lasting effects on the local environment and the global climate.
For buildings, darker, less reflective roofs mean the indoor environment is warmer, thus requiring more air-conditioning to maintain comfort for occupants. Higher cooling loads means more energy burned, CO2 expended, and air pollution created, not to mention higher operating costs. Second, the heat absorbed by the dark surfaces is picked up by the breezes and consequently increases the ambient temperature, which is measured several feet above the surface. For example, on a 90 degree summer day, the ambient temperature above an asphalt parking lot can reach 170 degrees, and lighter-colored grey concrete is about 120 degrees, while areas where there are trees is only 87 degrees! Not only does this heat island effect make it uncomfortable and sometimes unsafe for pedestrians, but it can be harmful to animal and plant life in urban environments. Last, there is the bigger picture of climate change and global responsibility. The warm air from the dark surfaces is absorbed by clouds and contributes to the greenhouse effect of a warmer planet.
Our recent work at 4th and Linden in downtown Long Beach reflects efforts to combat these consequences. One strategy is incorporating cool roofs, both by replacing the old dark roofs in the adaptive reuse EVCO complex, and by developing new infill construction on a barren asphalt parking lot across the street with white roofs. The small grey concrete parking lot in the rear of the EVCO complex was maintained – even though this still absorbs a significant amount of heat, it is an improvement over asphalt parking lots. The project avoided further heat island impacts by placing additional parking stalls within a portion of one of the buildings, under the shade of a cool roof. Further, the original building massing was reduced to accommodate a new landscaped courtyard and paseo. What began as a key architectural and urban design strategy to create shared open spaces, activate the street, and connect individual units, also turns out to keep temps low by reducing roof area in favor of landscaped space.
New large canopy trees placed in the courtyard and parking lots contribute to cooling, and as these native, drought-tolerant trees grow they will turn these hard impermeable spaces into shaded, cool spaces. Within the public realm, gaps were filled and palm trees were replaced with shady Drake Elms to support a continuous tree pattern and make the pedestrian environment more walkable. The trees will grow quickly – the sycamores planted will reach 40 feet in height in just four years.
The strategies employed at 4th and Linden are having a powerful effect not only for the users of the site, but also on the surrounding neighborhood. As our diagram above illustrates, the reduced heat island represents a noticeable dip in average temperatures. We can imagine what good can come out of employing these strategies – replacing dark roofs, planting trees, reduced parking requirements for new construction, and turning what parking we do need into lush parking courts – on other nearby sites.
Shade trees and courtyard along 4th Street create a comfortable walking experience
LEED Reference Guide for Green Building Design and Construction, 2009
“Cool Roofs Can Offset Carbon Dioxide Emissions And Mitigate Global Warming.” Terra Daily, July 21, 2010