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Posted by Jay J on June 22nd, 2000 10:41 AM
In reply to Radient barriers have been around for a good while in the Sun-Belt by J.C. on June 22nd, 2000 08:13 AM [Go to top of thread]

Do understand, folks, that I agree that you can put up a radiant barrier on the INSIDE of any room, attic include. The cavet is that the space is a 'livable space' AND it's been properly finished (attic or family room or basement.) Of course, each of us wants to keep heat INSIDE in the winter, and keep COOL air INSIDE in the summer. But to apply a radient barrier to an unfinished 'surface', like the underside of a roof's sheathing, defeats all logic and physics to me. Sooooo, ... Here ya go, guys. Here's just 1 site that talks about a radient barrier: Horizon Energy Systems

THEY say, and I quote:

Stapling RBS sheets under the roof is difficult, and causes accelerated roof temperatures leading to premature shingle degradation. When RBS is laid flat over existing insulation in sheet form, it offers itself to the accumulation of dust and a gradual decrease in reflectivity which reduces the performance. When applied as a multi-layed chip, the top layers become dusty while the layers below continue to block unwanted radiation for the life of your home...we know, its been tested (click here), by the Florida Solar Energy Center in 1989 and we have installations in dusty Phoenix since 1988.

For information on where to install RBS correctly, click here

Since the RBS Chip is designed to reflect heat flow away from your insulation, it's important to allow this heat to escape. We add dormer vents, soffit vents or power ventilators on every installation. Click here for info on attic venting.

Read the 'click here' links too. This is EXACTLY what I'm talking about. Are these folks wrong??!

And they say this on one of the 'click here' links:

1) Sheets of radiant barrier stapled inside the attic under the roof has been the recommended placement by the U.S. Department of Energy for several years. The graph clearly shows this application of radiant barrier to increase energy consumption and demand. Late in the day (4pm-5pm), the reflective properties of radiant barrier under the roof decking, faces the now superheated insulation and prevents heat from escaping. Heat becomes trapped in the attic much like a thermos bottle increasing demand and electical consumption.

2) Plywood laminated with radiant barrier has a similar effect though not as drastic as the rafter application. The explanation for this is simple once emissivity and convection are understood. The plywood roof deck, with a lowered emissivity due to the placement of radiant barrier, raises the temperature of the wood (much like a chrome car bumper on a sunny day). This in turn increases the convective currents in the attic which in turn superheats the insulation to a temperature higher than at home without radiant barrier! Manufacturers of this product claim lower attic temperatures at noon which can be seen in the graph above. It is not until 4-5pm
that the trapped heat becomes apparent and raises the need for electricity.

3) As can be seen in the graph, a radiant barrier placed directly over the insulation significantly reduces energy costs by keeping the insulation cooler. Our patented Radiant Barrier Chip product overcomes the anomolies once associated with this placement: performance degradation due to dust accumulation, labor intensive installations and moisture condensation in colder climates.


Jay J

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