
Radiant barriers reflect heat away during the summer and reflect it in during the winter. They are easily added to existing homes at little cost.

Radiant barriers reflect heat away during the summer and reflect it in during the winter. They are easily added to existing homes at little cost.
During college, I spent summers fighting forest fires in Northern California. At all times, we were required to carry with us a little pouch containing a fire shelter, which was basically a giant aluminum bag you were supposed to crawl into in the event you were surrounded by the fire and had to weather it out. As long as the fire doesn't touch the tent, most of the heat would be reflected away, saving the life of the person inside.
Radiant barriers use the same heat reflecting properties of aluminum installed in the attic of a home to reflect out the sun's radiant heat during the summer and reflect some heat back in the home during the winter.

According to LP Corp, a leading manufacturer of radiant barriers, homes with radiant barriers can save up to 17% on monthly home energy costs. In fact, radiant barriers are REQUIRED in newly constructed homes in ten of the 16 climate zones in California.
I recently visited a new home construction in North Carolina with the radiant barrier installed. In addition to the potential energy savings, it looked clean and increased the reflect light and visibility of the attic.

For new construction it makes sense, as you can by roof sheathing with the aluminum already attached to the bottom. It installs just like a regular roof, with the added benefit of a radiant barrier.
For existing construction however, there are options of adding the radiant barrier. RadiantGuard sells their Ultima product that can be stapled to the underside of your rafters, and for most homes would come in under $200 dollars.

But does it work? Some studies say it does. Does anyone have any firsthand experience? And which would be better, adding more insulation to an attic or installing a radiant barrier?
Resources:
LP Corp
Radiant Guard
Department of Energy on Radiant Barriers
My husband did his senior project on these. His results were not to the company's liking... the cost of installing the radiant barriers *in existing homes* did not cover the savings in electricity, given that the barriers degrade over time and are useless after 10 years. Installing new insulation is more effective.
Of course, since fuel prices have gone up quite a lot since that time, things may have changed.
In a new building, yes, installing a radiant barrier is a good idea, since adding the barrier doesn't increase the cost of labor by very much. But in his study, the barrier actually increased heating costs in winter by reflecting the heat out.
Provided you want to do this, though, one of the cheapest ways to retrofit a home to reduce heat is to paint your roof white. For aesthetic reasons, I don't think that'll catch on, though.
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This material works great on the inside trusses on the underside of roofs. Be careful to allow air to pass between the roof's plywood. It still needs to breath. The material has shown significant gains in the summer by reflecting the heat from the living space.
Steve Sanders-Home Improvement Contractor http://www.reducemyenergy.com
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