According to a study by the Building Envelope Research Program of the Oak Ridge National Laboratory, homes with air-conditioning duct work in the attic in the hottest climate zones, e.g., the deep south of the U.S., could benefit the most from radiant barrier interventions, with annual utility bill savings up to $150; whereas homes in milder climates, e.g., Baltimore, could see savings about half those of their southern neighbors. On the other hand, if there are no ducts or air handlers in the attic, the annual savings could be even much less, from about $12 in Miami to $5 in Baltimore. Nevertheless, a radiant barrier may still help to improve comfort and to reduce the peak air-conditioning load.
One common misconception regarding radiant barrier is that the heat reflecting off the radiant barrier back out the roof has the potential to increase the roof temperature and possibly damage the shingles. Performance testing by Florida Solar Energy Center demonstrated that the increase in temperature at the hottest part of the day was no more than about 5 degrees F. In fact, this study showed that radiant barrier had the potential to decrease the roof temperature once the sun went down because it was preventing the heat loss through the roof. RIMA International wrote a technical paper on the subject, where they collected statements from the largest roofing manufacturers, and none said that radiant barrier would in any way affect the warranty of the shingles.
Attic Dust Accumulation
When laying a radiant barrier over the insulation on the attic floor, it is possible for dust to accumulate on the top side. Many factors like the dust particle size, dust composition and the amount of ventilation in the attic will affect how dust accumulates and the ultimate performance of radiant barrier in the attic. A study by Tennessee Valley Authority mechanically applied a small amount of dust over a radiant barrier and found no significant effect when testing for performance. However, TVA referenced a previous study which stated it was possible for the radiant barrier to collect so much dust that its reflectivity could be decreased by nearly half. It is not true that a double-sided radiant barrier on the attic floor is immune to the dust concern. The TVA study also tested a double-sided radiant barrier with black plastic draped on top to simulate a heavy dust accumulation, as well as a single-sided radiant barrier with heavy kraft paper on the top. The test indicated that the radiant barrier was not performing, and the small air spaces created between the peaks of the insulation were not sufficient to block radiant heat.
Radiant barrier may be used as a vented skin around the exterior of a wall. Furring strips are applied to the sheathing to create a vented air space between the radiant barrier and the siding, and vents are used at the top and bottom to allow convective heat to rise naturally to the attic. If brick is being used on the exterior, then a vented air space may already be present, and furring strips are not necessary. Wrapping a house with radiant barrier can result in a 10% to 20% reduction in the tonnage air conditioning system requirement, and save both energy and construction costs.
Radiant barriers are also quite effective in floor systems above unheated basements and crawl spaces. The radiant barrier may be either stapled below the floor joists, creating a single reflective air space, or between the joists, followed by some type of sheathing. Radiant barrier works extremely well in this application for two reasons. First, a radiant barrier that is not perforated for breathability acts as an excellent vapor barrier. This means that ground moisture will not be able to pass through the radiant barrier and enter the living space. Secondly, the floor is the only part of the building where the heat flow is always down, unlike a roof where the heat would be coming down during the summer and rising to escape in the winter. When the heat flow is down, 93% of the heat is radiant heat, which is exactly what the radiant barrier is designed to block.