Here’s a picture of needless dependence and vulnerability. It’s a satellite picture of a residential neighborhood in Atlanta (also known as Hotlanta).
Atlanta, GA - Google Maps
What should jump out at you, thinking resiliently, is that almost all of the homes in the picture have asphalt roofs (I think that “rooves” sounds better, but I’ll acquiesce to convention). That’s unfortunate. These roofs will cook in the summer heat. Not only will these roofs drive up electricity costs for the home owner, but they will “tax” their neighbors as well through higher air temps.
In sum, an asphalt roof in a sunny, southern climate reduces your energy resilience. It similar to how buying a brand new car before you get the job and save the money that you need to effortlessly pay for it, reduces your financial resilience.
What’s the resilient solution?
The Cool Roof
Let’s start with a very simple idea. Energy resilience starts with how you manage heat, or more specifically: how you capture, shed, and store heat. For example: If you capture too much solar heat, you will need lots of electricity to power air conditioners that are needed to shed it.
In the case of roofs in sunny or southern climates, it’s all about shedding excess heat. How do you do that? With a cool roof. A cool roof uses materials that reflects or radiates the solar energy that shines on it. This allows a cool roof to maintain a surface temperature closer to the ambient temperature (the air temp). This in turn can reduce cooling costs by upwards of 20%, a big savings from such a simple solution.
How do you Cool your Roof?
There are lots of different ways to “cool” your roof. Here’s some insight that may prove useful:
- Cool roofing materials cost about as much as traditional materials. However, there are also pricey products out there, like Interlock aluminum roofs, that are popular in my neck of the woods.
- The color of the roof isn’t what makes it cool. Why? Most of the solar heat that hits a roof is in the infrared wavelength, which ignores color. So, it’s possible to have a cool roof that is dark.
- A common way to cool a roof is to add a reflective coating to an existing roof (painting shingles with light colored Acrylic paint has been tried by some DiYers to good effect).
- Even in many northern climates, the extra heating cost of a cool roof is negligible compared to the savings in cooling costs. In the extreme north (where heating dominates), there isn’t much of a positive impact from a cool roof.
How do common roofing materials compare? Here’s a pretty dramatic set of numbers. On a sunny day, roof temperatures can range from comfortably warm to egg-frying hot, depending on how much sunlight they reflect. Different roofing materials were tested side-by-side by Lawrence Berkeley National Lab researchers; their peak temperatures are listed below. Ambient air temperature at the time of the test was 55deg.F.
- Black acrylic paint: 142deg. F
- Galvanized steel: 138deg. F
- Black acrylic paint infrared-reflecting film : 123deg. F
- Common “white” fiberglass/asphalt shingle : 118deg. F
- Clay terra cotta tile : 112deg. F
- Red acrylic paint: 106deg. F
- Light green acrylic paint: 104deg. F
- White acrylic paint: 74deg. F
- Hyper white” acrylic paint : 65deg. F
Your thinking cool thoughts analyst,
John Robb
PS: As resilient communities mature, the surfaces that capture solar energy will be valued much more than they are today. Another way to look at it: what is wasted or seen as a nuisance in the failed globalized system will often be a propellant to the thriving localized system that replaces it.
