attic floor. While this method can be more effective in the winter there are a few potential concerns with this application, which the US Department of Energy and the Reflective Insulation Manufacturers Association International feel the need to address. First, a breathable radiant barrier should always be used here. This is usually achieved by small perforations in the radiant barrier foil. The vapor transmission rate of the radiant barrier should be at least 5 perms, as measured with ASTM E96, and the moisture in the insulation should be checked before installation. Second, the product should meet the required flame spread, which includes ASTM E84 with the ASTM E2599 method. Lastly, this method allows for dust to accumulate over the top surface of the radiant barrier, potentially reducing the efficiency over time. Energy savings According to a 2010 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, such as in the US Deep South, 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. Shingle temperature One common misconception regarding radiant barrier is that the heat reflecting off the radiant barrier back to 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 prevented heat loss through the roof. RIMA International wrote a technical paper on the subject which included statements collected from large 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