1/12/2024 0 Comments Radiant barrier insulationThat’s one reason power attic ventilators aren’t a good solution. ![]() So, the dominant form of heat gain in an attic is from radiation, which heats up all the solid materials it finds – framing, ductwork, insulation, all those boxes of Christmas decorations, and dead squirrels. Heat radiates from the roof deck to everthing in the attic.The radiant energy is absorbed by the roofing materials.You can see the heat transfer I just described in the diagram above: Typical roof decking materials – plywood and OSB – are pretty good radiators, so everything it ‘sees’ in the attic starts getting hot, too. When it finds the underside of the roof deck, it then can radiate down into the attic. That heat at the absorbing surface (shingles on most residential roofs) then does what the second law of thermodynamics tells it to do – it looks for cooler places, so it starts conducting down through the roofing materials. Once the roof sucks up those rays, it gets hot. The part we’re concerned with here is the sunlight that’s absorbed by your roof. ![]() How much of each you get depends on the wavelength of the radiation and the properties of the material it hits. When EM radiation hits a surface, it can do one of three things: (i) be reflected, (ii) be transmitted, or (iii) be absorbed. The heat from the Sun comes in the form of electromagnetic radiation. Attics get hot because the Sun is beating down on them all day. Unlike power attic ventilators, they actually go after the source rather than treating a symptom, but first, let’s look at the physics. OK, first of all, a radiant barrier is something that can keep your attic cooler. The general category of radiant barriers is an area of great hype, so I’ll tell you what I know, explain the basic physics, and show you some great resources for more information. I covered this topic a bit last year when I wrote about foil-faced bubble-wrap, a popular product for duct insulation and overblown R-value claims. ![]() So, today’s as good a day as any to talk about shiny stuff! I didn’t discuss radiant barriers in the article, but it’s a hot topic, so to speak, and someone did bring it up in the questions. In the guest post I wrote for Bob Borson in his blog Life of an Architect, I gave an overview of the types of attic insulation.
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