Mint Green: a wild and wicked approach to roofing a cabin

Subject: Mint Green: a study in the architecture of a roof Date: Friday, August 10, 2007 4:37 PM
Two weeks ago, the LP tank in the RV suddenly dropped to empty and we were out of hot water for the evening showers. The thought of burning up at least twenty bucks (at 6 mpg) in gasoline plus three or four working hours out of the day for that drive down the mountain caused me to think again about how maybe we could put that trip off for a few days by a resort to some sort of primitive technology closer to hand. When the sight of a pair of five gallon buckets, one white, the other black came to my eye out there under the sun, I figured that maybe we were suddenly, and for a first time most fortunately in the gas-free hot-water business. After filling both with water from the well, I set them out in direct sunlight to stand all day while we went back to work getting those rotten old shingles off the roof of the 1,200 sq. ft. log home we just bought (with some wooded acreage) and are in process of restoring to a livable condition.
Long about midday, upon my first check of the water temperature in those buckets, I found that science was not to be insulted in one of its most basic principles of physics concerning heat absorption and light reflectivity, in what would be otherwise known as the LRV or *light reflectivity value* when it comes to a variance of temperature pertaining to color.
The water in the black bucket was already risen to a comfortable bath temperature, whereas in the white bucket, the water was still cool to the touch. There are few things more satisfying in life than to see theory substantiated by experiment in fact and reality. I almost got a kind of 'rush' out of it, as they say in the crack house or out on the Rainbow Family Farm--and I continued to get off on it, as they say, the rest of that day as I slaved on under the hot sun scraping those black shingles off the roof.
This remarkable contrast between the black bucket water and the white had me thinking long and deep (and not a little angrily) about what was striking me more and more as the abjectly stubborn stupidity of roofing a building with a color of material that turns out to be lowest of all on the LRV scale, where white is 86.64 and black is 4.16!
"What manner of thick-headedness is this?" I had to wonder, as I went on hoeing those nasty, smelly black tiles off the roof and pushing them over the edge of the eaves on to a clear plastic sheet I had laid out over the grass below--such a horrible mistake as that, by the end of the day, would turn out to be. When we took up the sheet to empty all the detritus of asphalt and black roofing granules, we found that the lawn beneath had been burned to a beautiful shade of light, golden brown.
I gasped, staring aghast not so much at the fried grass as at the reality of what the sheathing on most people's roof-tops is being subjected to, at brunt of the same destructive cause: dark roofing materials cooking that roof, every day the sun is up there beating down on it.
I decided to try an experiment, now that I had seen first hand that my physics teachers hadn't just been whistling "Afternoon Delight", as to all the difference a color of material can make, and I was bound and determined to see might happen if someone were to be so confident in these principles as to actually break with some old dirty roofing habits and try a new thing.
I took a one foot square of Dow-Corning 3/4" sky blue Styrofoam panel and nailed it down to the now bare plywood surface of the roof, and left it there. Now of course you can read up on all the dope of do's and don'ts from Dow itself as to the specifications for this material when it is used strictly to a purpose of roof insulation . . .
http://files.buildsite.com/dbderived-f/dowchemical/derived_files/derived7344.pdf
Clearly, what I had in mind was not unprecedented--for insulation. So, you can imagine the sense of satisfaction that came by the touch of a hand, to feel the contrast in heat between the light brown surface of the bare plywood, and that of the light blue Styrofoam. It was totally, "Wow!" The plywood was hot to the touch while the Styro was cool by comparison, just perhaps around air temperature or that of a lukewarm bath.
Then, just to be on the safe side of a greater certainty, I decided to leave that square of Styro up there under full sun, through peak daytime temps of +92 degrees for two more days. Yesterday morning, as I climbed down the ladder from the roof, just before taking off for our house in town, I was happy to jump behind the wheel in the Blazer and announce to my Baby that there had been absolutely no visible deterioration to the Styro--none whatsoever.
I have long been a firm believer in the proposition that modern mankind gets stuck, more often than not in stubborn old habits that we get mistaken for the 'state of the art'. We keep using heavy, expensive, smelly old materials from a bygone era that technology has since made obsolete--if only we could know that by suddenly recognizing the new material and method that is here to replace the old.
Here is the idea . . .
You are hardly going to find a membrane less permeable to moisture than Styrofoam--whether by direct penetration or osmosis. The stuff is just flat out water-tight, as I have been able to observe, once again by experiment, putting water over its surface and waiting long hours to see if any gets through. None does.
But Styrofoam is soft and highly subject to damage by impact of whatever might come flying through the air; hail, sticks, bird-beaks and claws, name your favorite fine-feathered or furry varmint, like your wife's most beloved cat. Because of that, Styro must be covered by something to protect its highly vulnerable surface. Even so, the fact remains that those Styro panels can be caulked along every edge, peak and valley, to make of the entire roof one water-impermeable surface. Now that *is* the roof, and all it needs is something to shield it which theoretically need not even be water-tight. Had you a mind to get all wild and wicked, you could strap a bunch of bare wooden lattice up there over the Styro covered by a layer of window screen *(to keep the leaves and crap out of the gaps) and paint . . .
By damn! Even as I sit here rethinking all this (as first written yesterday) I begin to realize how wildly, wickedly ventilated such a roof would be, all aerated by a lattice-work of treated wood the color of wooden shakes like that, and if you were to ask me, I'd say that it would look damned nice!
In any case, here's the rest of what I had (yesterday) before this Satori-like thought came to sit on my mind like a fat, but feather-light outrageously laughing Buddha . . .
In a manner of speaking it almost doesn't matter what you put over the Styro for a shell so long as it does not defeat the other primary purpose aside from shedding water--that of reflecting heat. In any case, the Styro would have to be painted for protection against UV radiation, as according to considerations revealed by a fine study done in Florida on the feasibility of working with something developed by NASA for the Space Shuttle in the form of the "elastomeric" ceramic micro-sphere technology--as a paint additive.
http://www.fsec.ucf.edu/en/publications/html/FSEC-PF-293-95/index.htm
Such products e.g. "Kool Seal" are on the market already mixed, and the LRV of the white, rubberized coating, for the first year or so before dirt, mildew and staining had a chance at it, was high enough to result in so much as a 60% reduction in air conditioning costs--according to that study backed by some pretty fancy looking science.
But as some people have cause to complain about the eye-strain impact of a bright roof, a few communities as e.g. in Arizona have outlawed the stuff--and I don't know that I blame them--as I think about that red metal roof lately installed across the street from my house in town, the way that sucker reflects heat and light. While storm clouds are rising, I have been known, a time or two, to get out on the lawn for a few quick rain dance Boogaloo steps, in conjuration of a thunderstorm with golf-ball or better sized hail, just to serve that neighbor right. And, upon wishing not to be like that tin-roof lodger over there, I have had much thought toward a better, kinder more neighborly idea.
There is a fairly informative article entitled "Paint it Green" on the "green technology" of LRV factors and that NASA micro-sphere technology when it comes to such an additive in the various colors and shades of paint . . .
http://www.metrosantacruz.com/metro-santa-cruz/04.25.07/green-paint-0717.html
And you can access a list giving the precise value for nearly every color and shade in the rainbow . . .
http://www.apcosigns.com/techpdf/lrv.pdf
What led me to that Santa Cruz site was a search on the keywords "green" and "LRV", going on the hunch that the color green, in its lighter shades might prove to have a higher LRV than most any other. The above-linked list bears the hunch true, as it turns out that e.g. "Mint Green" is higher on the scale even than the lightest shade of yellow.
Well! it only stands to reason that trees and most all plant life with the kind of sun exposure they get, would evolve with a color scheme for their foliage which would be least susceptible to burning from UV sunlight radiation. Most plants do not have blue leaves, so I figure that we should not have a blue roof, but a Mint Green one for that log cabin.
Here's the plan . . .
We invest in some of that unpigmented translucent fiber-glass corrugated roof sheeting to serve as the shell over the Styro and we paint the Styro the color we like, namely Mint Green--and maybe we'll even go so far as to paint the underside of the shell Mint Green, too. As shown by the list . . .
http://www.apcosigns.com/techpdf/lrv.pdf
. . . of all colors, short of the various shades of white, Mint Green is highest on the LRV scale at 75.80, higher than Sky Blue at 65.80 (no wonder the Styro was so cool to the touch out in that sun), the Satin Silver at 52, the Chrome Yellow at 42, and the Buff at 53.40.
Back to the Styro: Two more advantages are these: since it is soft and compressible like a sponge, you can buy the 'ship-lap' sheets, fit them together with no necessity of allowing for contraction and expansion as with all other forms of sheathing. And yet, so spongy as that stuff may seem, as the weight of anything put down over it gets distributed, it is remarkably capable of sustaining its depth without being depressed even to the extent that we were able to underlay the air-conditioners on the roof of our RV (to stop leaks) with Styro sheets at the beginning of this season with as yet, no visible change in 3/4" depth of the material. You can crawl on it with your knees (while cutting) or even walk on it--carefully--with minimal effect to the surface.
The stuff holds up, and due to this virtue, our plan continues as follows . . .
We'll lay down the adhesive, the Styro and caulk it. Either we'll paint that or simply undercoat the fiberglass corrugated sheets--maybe both. The fiberglass sheets will be pre-drilled for the screws, and we'll use the neoprene washers. Finally, although we might fully trust that the screws through the Styro would be self-sealing--for peace of mind, we'll dip every screw in silicone just to be on the safe side.
Any objections? If so, I want to hear them before I wind up sitting up there drenched to the drawers under that roof with nothing to show for it but a cold shower and a bunch of Mint Green paint chips offering a fine contrast to a cherry red face so wet that you could not tell the teardrops from the rain.
--
Mackie
http://whosenose.blogspot.com
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