In the guest post I wrote for Bob Borson in his blog lifetime of an Architect, I gave an summary of the kinds of attic insulation. I didn't discuss radiant barriers within the article, but it is a hot topic, so to talk , and someone did bring it up within the questions. So, today's nearly as good each day as any to speak about shiny stuff! So here I am as a Home analyst give you the full sugestion about the Radiant Barrier Fundamentals for Your Home Needs!


I covered this subject a touch last year once I wrote about foil-faced bubble-wrap, a well-liked product for duct insulation and overblown R-value claims. the overall category of radiant barriers is a neighborhood of great hype, so I'll tell you what i do know , explain the essential physics, and show you some great resources for more information.

OK, first of all, a radiant barrier are some things which will keep your attic cooler. Unlike power attic ventilators, they really follow the source instead of treating a symbol , but first, let's check out the physics. Attics get hot because the Sun is thrashing down on all of them day. the warmth from the Sun comes within the sort of electromagnetic wave . When EM radiation hits a surface, it can do one among three things: (i) be reflected, (ii) be transmitted, or (iii) be absorbed. what proportion of every you get depends on the wavelength of the radiation and therefore the properties of the fabric it hits.

The part we're concerned with here is that the sunlight that's absorbed by your roof. Once the roof sucks up those rays, it gets hot. That heat at the absorbing surface (shingles on most residential roofs) then does what the second law of thermodynamics tells it to try to to - it's for cooler places, so it starts conducting down through the roofing materials. When it finds the underside of the roof deck, it then can radiate down into the attic. Typical roof decking materials - plywood and OSB - are pretty good radiators, so everything it 'sees' within the attic starts getting hot, too.


You can see the warmth transfer I just described within the diagram above:

  • Radiation hits the roof.
  • The energy is absorbed by the roofing materials.
  • The thermal energy conducts downward.
  • Heat radiates from the roof deck to everthing within the attic.


So, the dominant sort 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. That's one reason power attic ventilators aren't an honest solution. they go after the air, but the air is hot only because all the solid materials are hot.

A better thanks to reduce the attic temperature is to travel after the source - the radiation constantly blasting the attic from rock bottom of the roof deck and rafters. Plywood and OSB are good radiators. In physics language, they need high emissivity, which suggests they're good at emitting energy .

That's where radiant barriers are available . These are materials that have a coffee emissivity. When the underside of the roof deck features a radiant barrier installed, the warmth still travels through the materials, but once it hits the radiant barrier, it's come to a dead end. Little of that heat then radiates to the attic.



The radiant barrier gets hot. If you go up into the attic and touch it, you will see that the heat's still getting there. But like that chrome steel playground slide, once you hold your hand near it without touching, it doesn't desire it's hot. The magic of low emissivity! just in case you're wondering, the solution is yes, this is often an equivalent thing that creates 'low-e' windows so good. Also, if you're wondering how hot the shingles get, the Florida solar power Center has done research thereon , which I wrote about last year.

OK, so if the radiant barrier doesn't feel hot once you hold your hand an in. away but it can burn you once you touch it, what does that mean for installation? you bought it! you've got to possess an air gap next to the radiant barrier. If you spray foam insulation right the radiant barrier, you've wasted your money thereon . Heat will conduct throughout the radiant barrier because generally, materials with low emissivity have high conductivity.

There's such a lot more to mention about radiant barriers, but let me conclude this text and provides you a few of resources where you'll read more about how they work, the way to install them, what proportion they could save, and why you almost certainly don't need to put in one in Pennsylvania. the primary is that the Florida solar power Center (FSEC). they need a touch of radiant heat gain in attics down there and know a thing or two about this subject . Here's an honest Question and Answer Primer that's got tons of excellent info. Oak Ridge National Laboratory, which does tons of great building science research, has several good pages about radiant barriers, too.

I'll come to the present topic and write more once more , except for now, let's not forget what my friend Mike Barcik says is one among the simplest things about radiant barriers - People like shiny stuff!

Then, If you also want then you can get then another idea about How an Installed Radiant Barrier Works