The Arizona Republic
Recently, the focus has been on whether to install a radiant barrier in your attic where temperatures can climb as high as 140 degrees in summer. The idea of eliminating some of that hot air overhead can be appealing. The radiant barrier industry has been growing in hot climates like Arizona where even the U.S. government says these barriers work more effectively than in cold climates.
What is a radiant barrier? According to the Department of Energy definition, it’s a highly reflective material that reflects -- or emits -- radiant heat rather than absorbing it. A radiant barrier doesn’t work the same way as the thermal insulation in your attic that slows the entry of hot air into air-conditioned spaces downstairs.
Radiant barriers come in several forms including reflective foil, reflective-laminated roof sheathing and metal roof shingles.
According to Scott Petre, a manager with Banker Insulation in Chandler, the best way to use a radiant barrier in an existing house in Southern Arizona, is to install a foil-type barrier stapled to the trusses in your attic. The material should be installed leaving a space at the ridge and at the eaves; that way the heat can flow out of ridge vents or gable vents in your roofing.
A single layer of radiant barrier insulation can also be put on over asphalt shingles when a homeowner lays a metal roof on top of the old roofing.
Of course, having the right radiant barrier correctly installed is vital. You can buy radiant barrier material and put it in yourself, but it is important to put it in properly to get the desired result. The type of radiant barrier that is simply laid on an attic floor will deteriorate quickly in Arizona because of heavy dust accumulation over time.
What a radiant barrier will cost, including installation by an experienced and reputable contractor, will vary depending on several factors including how big your house is, how accessible your attic is, and what type of radiant barrier you choose.
There are several manufacturers of radiant barriers and many products to choose from; it is important to look not only at product performance and cost, but make sure the product has been tested according to American Society for Testing and Materials Standards.
At Rosie on the House, we tend to think that a much better investment than over-insulating your attic or adding a radiant barrier is ensuring that you have R-30 to R-38 insulation that has been properly installed. The smallest deviation in how it should be used in your attic can make a difference in its performance.
According to Jerry Thieken, an energy consultant with SRP in Phoenix, a homeowner with R-30 to R-38 insulation, probably won’t get much more help from a radiant barrier. “If you have R-19, for example, it could be more cost-effective to upgrade your existing insulation,” Thieken says.
The real debate about radiant barriers, as with any insulation, is whether it warrants the cost. Everyone agrees it provides savings on air conditioning. The Department of Energy says in general that radiant barriers “can lower cooling costs between 5 to 10 percent when used in a warm, sunny climate.” Fi-Foil, a Florida manufacturer of barriers used in the Phoenix area, says that AC savings can be up to 10 to 12 percent.
Want to compute your maximum possible savings?
Let’s use a typical all-electric Arizona home of 2,000 square feet – three bedrooms and two baths for a family of four. The home’s usual March utility bill is $200. That’s what we call the base load with no air conditioning. The August bill is $400, indicating that the cooling cost during the hottest month is $200.
Let’s say that the attic in this home accounts for maybe 12 to 15 percent of this cooling cost in terms of heat coming through the ceiling and into the living space. In other words, using a figure of 13 percent, a hot attic costs maybe about $26 a month in the summer and much less in late spring and early fall.
Multiplying that $26 by four months totals $104. If we include April, May, October and November, the air conditioning cost due to the attic is nearly zero. But let’s make it $10 times four months. Now the total cooling cost for this typical house due to heat load from the attic is $144. Compare this to the estimate for installing a radiant barrier to determine how many years you have to stay in the house for a reasonable return on investment.
Most estimates I’ve seen for installing radiant barriers are in the thousands of dollars. This equates to a payback lasting decades, not years. To me, the numbers say that from a pure return on investment analysis, radiant barriers are not the place to start a campaign to save money on your cooling bill.
If you are still interested, choose a long-time trusted insulation contractor to put in your radiant barrier. There are companies that drop into Arizona temporarily during the hot season to install radiant barriers, plus unnecessarily thick insulation for outrageous prices, and then disappear. Look for a reputable firm that will quote you a fair price.
Another note about attic cooling: At Rose on the House we never recommend powered attic ventilation without consulting a mechanical engineer to ensure that that electric fan won’t actually raise your energy bill in summer.
Check back with us next week when we start a series of articles on home security. We will be talking about creating an inventory of your valuables for use in case of theft or fire.
For more do-it-yourself tips, go to rosieonthehouse.com. An Arizona home building and remodeling industry expert for 35 years, Rosie Romero is the host of the Rosie on the House radio program from 8-11 a.m. Saturdays on KTAR-FM (92.3) in Phoenix, KQNA-AM (1130) in Prescott and KAZM-AM (780) in Sedona, KAFF-AM (930) in Flagstaff and KNST-AM (790) in Tucson. Call 888-767-4348.