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Wednesday, November 23, 2011

Ventilation or Radiant Barrier?

This post is like eating watermelon in January. it is out of season. But as winter here last about two weeks and summer can last up to ten years, I wanted to beat the heat to the punch, because if you're buying a roof now, don't forget about Ra, Huitzilopochtli, Mithra or Apollo. They won't forget about you when your inadequate attic becomes the blast furnace that eats you alive.

The raging debate amongst the illiterati is whether to vent or to reduce heat with all the newfangled products like Cool Series and Energy Cap by GAF, Solaris by Certainteed, Energy Star colors by Gerard Roofing Technologies, or the new underlayments like Polarium and Energy Q. Below that is the best of the best, Techshield and the imitators like Solar Board. The radiant barrier foil backed decking is, hands down, the best. Painted on reflective coatings and staple on foil don't work near as well.

As heat goes where heat isn't and aluminum has very low emissivity, having the foil on the decking is the best place to have it. Putting it on the attic floor is a giant mistake because convected head lives there and the foil gets loaded with dust. Then all sorts of bad stuff happens. Like your ceilings fall in from humidity!

The answer is in the balance of the two, just like when Plato, using Socrates as his mouthpiece in "The Republic" asks if it is better to use the old country doctor who knows what works or the recent graduate of medical school who knows why something works. Even though this book was written over 2300 years ago, the debate rages.The answer is neither. You want both, the experienced doctor who keeps up his education on leeches, blood letting and spells. (you know Hippocrates called vinegar the first medicine and raw unpasteurized vinegar with mother mixed with local honey cured me of arthritis, acid reflux, and allergies.)

Back in the attic the sun's photons are doing their job and making the temperature rise to millions of degrees kelvin and the pot roast went from frozen to done in minutes. So what's a homeowner to do? Both!

Here's the math: reduce the load in factor of heat with any of these Energy Star products and keep the Venturi Effect racing from the soffits to your favorite exhaust point and the attic won't fill up with excited molecules that keep running into each other because they are hot. Less heat gain and more heat removal equals an attic closer to ambient temperature.

If you use foil faced decking, make sure it is not applied directly to the lathe of the old wood roof because the near 50% coverage results in a lot of conduction. This is why aluminum was used for wiring for years. it conducts. This will super heat your attic.

But ventilation also works in the winter by keeping down humidity and preventing ice dams. If covering your turbines makes your house warmer, you have major problems. you need that old fashioned energy saver called insulation. Once the heat passes your sheetrock, it is gone. Warm attics help no one. You always want your attic to approximate outside ambient temperature. Don't cover your turbines! Never, unless they are leaking. That's leaking water or lava into your attic, not heat outside, contributing to global warming, a plot by the Greenlandic scientists to increase tourism.

Less in, more out. That's the ticket.

Jon Alan Wright
Jon Wright Roofing, Siding, and Windows
1915 Peters Rd., Suite 310
Irving, TX 75061
972.251.1818 Office
214.718.3748 Cell
972.554.8090 Fax
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1 comment:

nat said...

hey john,
When redecking over lathe with the foil faced decking, how do you do it? In the past, I have removed half of the 1x4s leaving the rest at about 14 to 16" centers then decked vertically. Of course, this easily doubles the labor which I don't get paid for enough. I have seen so many slap on roofers who totally screw it up.

ed senter