Walking around a hot city in the middle of summer is not a pleasant experience. The sun bouncing off everything causes buildings, the ground, and absolutely everything to absorb the sun’s rays and retain heat. The hottest days turn into hot nights, with buildings continuing to give off heat until dawn. This is called the urban heat island effect, where the concentration of dark materials, asphalt, brick, and roofs makes the city up to 20°F hotter than surrounding areas with vegetation.
However, one of the most important cities in the southern United States, Atlanta, is adopting a different and simple strategy in urban design to try to combat the harsh summer months. From now on, the “cool roof” law will be enforced.
The Reflective Solution for roofs
The city of Atlanta, Georgia, recently passed municipal Ordinance 25-O-1310, which requires roofs to be installed using materials with a high solar reflectance index, in addition to using light colors. These materials reflect sunlight and prevent heat absorption. Obviously, this law currently only applies to new construction and roof replacements. Buildings that are in good condition and do not need maintenance will not have to change their roofs.
This has come about thanks to Councilwoman Liliana Bakhtiari, who has shown calculations of an average cooling of 2.4°F in the city. With proper use of this construction technique, they hope to avoid up to 6.3°F in the most vulnerable neighborhoods. By preventing buildings from overheating, it is estimated that $310 million will be saved in air conditioning energy bills over the next 35 years.
How to avoid summer heat retention
In addition to building reflective roofs, one of the most effective ways to keep temperatures down during the warmer months is to use vegetation. Planting trees is a very effective measure.
In addition to providing shade, a phenomenon called “evapotranspiration” occurs: plants release water vapor, which requires energy (heat) from the surrounding air, actively cooling the environment, like natural air conditioning. On the other hand, the tree canopy prevents the sun from heating absorbent surfaces (asphalt). The perceived temperature under a tree can be 19°C lower. You have probably noticed in summer that it is much more bearable to walk down a street lined with trees than one where the sun’s rays beat down aggressively on the sidewalk and asphalt.
Trees can be planted not only on sidewalks but also on green roofs, which provide a layer of insulation and stabilize the temperature in the buildings where they are installed. In addition, large urban parks (such as Central Park in NYC or the various parks in London) are capable of cooling entire neighborhoods by up to 9ºF.
Let’s go old-school
There is a somewhat outdated method that prevented sunlight from overheating a building. We are talking about awnings, which fell out of fashion when air conditioning was invented for single-family homes. However, they are an excellent passive technique for preventing your home from overheating. You only need to install them once, and your electricity bill will plummet in the summer. By blocking the sun’s rays before they enter through the window, you avoid the greenhouse effect that would occur if you had uncovered windows with flimsy curtains. Awnings are also retractable, allowing solar heat to enter during the winter months.
Awnings are one of the most cost effective, electric-bill reducing ways to make sure you do not need to crank down the temperature in your air conditioner. The whole building remains cool if one of it’s weakest points—glass windows— remain protected from sun rays.
For now, we’ll wait and see how the city of Atlanta manages to lower the temperature in its communities during the summer months.