Should I install a radiant barrier?

Should I install a radiant barrier?
25 August 2007

A couple of weeks ago when I was discussing ways in which to lower one’s electric bill I mentioned increasing the depth of insulation in the attic. All in all a good idea. Like money in the bank, more is always better. However the ten inch target depth that I mentioned is an older standard. Andrew Cameron of AC&R Insulation contacted me reminding me that most counties in the state now require an R38 (15.3") in the attic with new construction, while the U.S. Department of Energy recommends even more R49(19.1") of blown fiberglass. I told Andrew that I routinely see only about three or four inches of attic insulation in the majority of the older housing stock I inspect. He knew that. Bulking up insulation in the attic is truly money not only well spent but that will come back quickly through energy savings.

Q. I’ve been seeing information recently about energy saving aluminum radiant barriers. From what I’ve seen the barriers are fairly effective even for the novice because even with minor imperfections in the installation process they are still effective a nd can save energy. They sure sound good to me but I have two questions that the literature I’ve seen doesn’t address. First, everything suggests that you can save money and energy in southern states. Does this mean that those of us in the mid-Atlantic area would not realize a savings or should not use this product? Second, if as the installation instructions suggest, you place the barrier on the underside of the roof. What effect does it then have on the roof and shingles thereon? Presumably it blocks 95 percent of the heat radiated down by the roof. A radiant barrier sounds like a good idea but is it suitable for our area?

A. There’s some truth to what you’ve been reading. I've seen tons of technical data on reflective barriers and under certain circumstances researchers actually measure quite a difference. However with an adequately insulated ceiling-- see above--and with proper ventilation, I don't think you will gain much by using one. And under certain circumstances a barrier can even cause trouble.

There’s the unanticipated consequences to consider. The single-minded quest for a certain result by employing a certain method oft-times ignores what else might occur by the use of the new method. The two words that scare me most with a reflective barr ier are "reflective" and "barrier". I recently saw a TV documentary where they lit the Olympic flame with a reflective dish using the sun's rays. I don't think your reflective barrier would do that to your shingles but keep the concept in mind. And th e notion of a barrier to me suggests a possible under-roof condensation surface when the sun's not shining. Big trouble.

The way roofs age is the sun cooks the asphalt life out of the shingle over time. Putting a reflective barrier under the shingles in the attic may even shorten shingle life. And I don't like any sort of barrier in such an application in the attic as a p otential condensation surface. Moisture migrating via vapor pressure from the warm house during cold weather is a powerful force and if you block it you’re asking for grief. The end results possibly costing you the whole roof--wood framing and all.

The key is proper ventilation working in concert with insulation. We live is a climate that is both a heating and cooling climate-- a bit more cooling than heating. I have seen roof systems designed around radiant barrier systems and all the negatives-- including roof covering type-- were taken into account. Where they are most effective is in structures that are essentially uninsulated such as large agricultural buildings that can heat to unbearable levels in the summer sun. Radiant barriers are a goo d idea for many applications but I don’t recommend trying to retrofit one into your attic.