While we must admonish our ancestors for their foolish fashion choices, we also must admit there are numerous things they did to make use of what few cooling tools they had, and we would do well to emulate these strategies. For starters, the orientation of their houses was often chosen more for the ability to capture prevailing afternoon breezes through the dog run that was a staple in early 19th century Texas farm houses. On a 100°F afternoon, the porch would often feel 15-20 degrees cooler than the fields.
Similar effects could be found in the placement of arbors about the grounds. At Barrington Farm, the slave quarters are surrounded by grape arbors whose purpose is less about fruit, and more about shade. Again, taking advantage of orientation and the afternoon breeze, we once visited the farm during corn harvest, and despite the high heat and humidity, the guide was happily roasting corn over an open fire, from under the shade of a muscadine trellis.
Another thing we noticed at Barrington Farm the last time we visited was that “the big house” was painted the brightest white imagineable. We particularly made note of this fact because we last visited about the same time that we decided to paint our tin roof white for the purpose of cutting our cooling costs.
Non-white roofs are the modern equivalent of the lunacy of wearing corsets in 100° weather. To put it simply, the laws of physics are either your friends, or your enemies, depending on how stubbornly you adhere to social norms in the face of real needs for change. Light colors absorb less heat energy and both reflect and emit more heat energy, while darker colors absorb more heat energy and both reflect and emit less heat energy. In plain English, a dark-colored house with a dark-colored roof makes no sense whatsoever in a Texas summer.
Traditional roofing surfaces in the United States can reach summer peak temperatures ranging from 150-185°F (66-85°C), which not only makes it much more difficult to cool the building, but also contributing to something called the “urban heat island”. When you consider that the average city is approximately 20% rooftop by area (per a survey done from 1998-2002), that means there is a considerable amount of heat being retained in our cities by black tar, gray slate, and other dark roofing materials which amplify heating problems, making bad situations worse.
There are several solutions to this problem, the best of course being to encourage the growth of trees tall enough to shade not just your yard and maybe a few windows, but also the roof of your home. Sunlight which never reaches the surface cannot, obviously, contribute to excess heat. Barring the advent of magic beans to make your trees taller, however, the next best solution is to change the surface of your roof to reflect more sunlight and emit more heat into the atmosphere and away from your home. That’s where “cool roof” technology takes over.
Cool roofs are basically just like normal roofs, with one of two differences – either a coating which adds albedo (reflectivity), reduces absorption and increases emission; or else a basic material which accomplishes the same functions. An example of the kind of coating we are talking about is the specialized white paint we used on our own home. Available at all major hardware stores, and many of the minor ones, look next to the roofing materials rather than in the paint section because while this is technically “paint” it is not like other paints.
To begin with, most house paint is not designed to be applied to surfaces which regularly reach 180°F. Further, this stuff is designed to be laid down in a fairly thick swath. We used a regular roller to apply it to our metal roof, but it would not be amiss to suggest simply pouring out a quantity on the area you are wanting to cover and then using a push-broom to even it out at 1/8th to 1/4th of an inch thickness.
There are other kinds of roofing paints, including a cementitious paint (paint with cement material), and a combination of cement and polymers. The advantage of the polymers is that they provide a waterproof seal; the cementitious paints would only be practical on surfaces which are themselves already impermeable – we could have used one ourselves had that been our only option, but we painted our roof long before we learned all the different elements of cool roof technology.
In addition to paint, there is also the option of using a polyurethane foam barrier on a rooftop. This is common on commercial buildings; Texas A&M started putting this type of cool roof on buildings as early as the early 1970s, and that same technology is fairly common all over the country even today on new school construction, as well as in some industrial and warehouse developments.
Finally, rather than using a coating, there are the cool roof building materials, where the roof itself is simply built from material which has high reflectivity and emissivity. An example of this type of material would be a white vinyl sheeting, used instead of traditional shingles or metal sheeting. By contrast to asphalt (which has a reflectivity between 6 and 26%), white vinyl rooftops reflect more than 80% of the suns rays, and emit at least 70% of the solar radiation the building absorbs. Depending on roof tilt and latitude, a white vinyl roof is the cool roof champion.
One final strategy worth mentioning is the ‘green roof’ system. Particularly common with rammed earth and strawbale houses, a ‘green roof’ is literally a roof with a garden on it. While it takes some sound engineering to guarantee the necessary load-bearing qualities of the structure below, a ‘green roof’ provides some of the soundest thermal principles for environmental control of a building you could wish for – in summer, the solar energy is absorbed by the plants growing on the roof, and converted into leaves and (possibly) fruit and produce. While the soil will undoubtedly absorb more energy than it can possibly emit back into space, it provides far better insulation than is found in most attic spaces.
And in winter, this natural insulation makes a green roof practical in northern climates in ways a typical cool roof might not – although heat loss in winter from the roof is greatly exaggerated; the greater danger is from excessive draftiness, not from albedo and emission.
The principal advantages of cool roofing technology apply to the individual buildings where these technologies are applied – whether a domestic building where a family lives, or a warehouse where goods are stored, or a factory, where people and machinery require constant environmental controls – but there are additional benefits to the greater community, as well. Municipalities with the forethought to subsidize cool roof technology see almost immediate impacts in the mitigation of the phenomenon known as an “urban heat island”.
As long ago as 1818, amateur meteorologist Luke Howard described the effect in his seminal work The Climate of London, wherein his careful observations of wind direction, barometric pressure, temperature and precipitation led him to conclude that there was an ineffable something about the urban environment which made it warmer and drier than the surrounding countryside.
Thanks to the far greater scope of data available in the 21st century, modern meteorologists are able to model urban heat islands far more effectively. Basically, the darker synthetic materials used in urban construction (asphalt roadways, dark colored bricks, dark tile roofs, the darker shades of cement) absorb far more heat and emit far less back out into space than would be true of the more natural materials found in greater quantities in suburbia and the countryside.
For an experimental confirmation of this idea, try standing barefoot at noon in a garden bed, say in the shade of a nice rosemary or basil plant, and then stand on the sidewalk – most sensible people would just take our word for it, we think.
Several factors combine to make this phenomenon worse in some cities than in others – “tunnels” created by skyscrapers focus heat energy in some downtown neighborhoods and prevent its easy escape; other cities get lucky in the orientation of prevailing winds, or maybe juxtaposition to the ocean gives the heat sink an easy drain for some, while being situated in a desert basin causes others to simply sit and bake.
And sometimes seemingly unrelated weather events are the direct result of this island effect. There is an unofficial term related to College Station weather, the so-called “Aggie Dome” which prevents rainfall on relatively small scale. We cannot count the number of times we have sat in front of the radar, watched massive storm systems move into the area, headed directly towards us, only to see those same systems break apart just outside the College Station city limits, only to reform once the system reaches the other side of town. This happens whether we are talking about Pacific moisture streaming up from across Mexico and the Rio Grande region, or Gulf moisture streaming up from Houston and Galveston, or with a Pacific cold front sliding in from the Northwest.
Likewise, the folk wisdom that if there is a trailer park in a town hit by a tornado, you can be sure the tornado will find it, has more truth to it than one might imagine. Trailer parks, you see, are more likely to be on the outskirts of a town… and thanks to the urban heat island, that is also where storm systems are most likely to be. The air over the heat island is hot and dry relative to the air in the neighboring environs; as a consequence, there is updraft and an outward force pushing against any incoming downdraft and incoming force.
Cool roofs help counter these effects by muting the initial warming quality of the urban surfaces. Over twenty years ago now, the City of Atlanta started working with cooler technologies, and they are just one of dozens of communities where engineers have discovered that replacing blacktop roads with lighter colored materials can reduce urban temperatures by several degrees. The difference between 100° and 97° may not sound like much to a Yankee, but to us at Myrtle’s it sounds like a pretty huge difference.
Anybody who doesn’t currently have a cool roof, you’ve been placed on notice – next Spring, we expect to see you climbing a ladder, carrying a big white bucket with a paint roller.
Keep cool, and
Happy farming!
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Just now catching up on my reading! You were only three the first time I took you to Washington-on-the-Brazos. I doubt you remember. You might also note that YOU are a Barrington descendent. Re your description of the white roof phenomena: This is the same principle for buying white cars. They reflect the heat. I have no stats on this, but driving a white car in Texas makes a lot more sense than the shiny black or dark blue ones. Mother Hen
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