Answers:
- An R-Value is a measurement of resistance to the flow of conductive heat transfer. Since Radiant Barriers are designed to reflect radiant and not conductive heat, they do not have an actual R-Value. Any "theoretical" or "equivalent" R-Value depends heavily on the method of installation and the size and number of airspaces surrounding the material. We do not attempt to assign any R-Value to Radiant Barrier as it is not relevant and somewhat misleading. It is the RB's ability to reflect radiant heat that makes it such an energy saver.
- It depends on your application. Here is the general rule of thumb. If you are installing the Radiant Barrier on the outside/exterior of mass insulation, use the Perforated type so as not to trap moisture in the insulation. If you install it on the inside/interior of mass insulation, use the Solid type and tape the seams to create a vapor barrier. We recommend using only perforarted radiant barrier in all attic installations.
- Yes, the holes are very small and do not degrade the performance of the RB. They are there just to allow moisture to pass through and have virtually no effect on the thermal performance.
- When using Radiant Barrier as a Vapor Barrier or housewrap, it is important to seal all the seams. You will need approximately 1 roll of tape (2" x 150') for every 1000sf of Radiant Barrier. Most other installation types generally need little or no tape.
- Yes, most definately! There are two properties which allow radiant barriers to work, reflectivity and low emissivity (low-e). Heat is reflected on the top/hot side, and since RB has a low-e value, heat is not emitted to the bottom/cold side. Of these two properties the low-e value is of greater importance. In order for a radiant barrier to be most effective in both summer and winter it needs to have aluminum on both sides. According to a study performed at Texas A&M University, double sided radiant barriers were 41% more effective then their single sided counterparts.
- Your actual savings will vary with many factors including: attic installed location, house shading, duct leakage, air handler location, geographic location, etc. In the South, you can expect to see a 40% reduction in heat gained through the ceiling. This can translate to a 17% savings on cooling bills. In some installations, there will also be additional savings on heat lost through the ceiling in the winter.
- The Radiant Barrier will only increase the roof surface temperature by 2 to 5 degrees. To put it in perspective, the surface temperature of dark asphalt shingles can reach 190°F on a hot sunny day. Most roofing manufactures recognize that adding radiant barrier to your attic will not harm your shingles.
- The most important specification to look at when comparing different types radiant barrier is the emissivity value. This is a number ranging from 0 to 1, and the lower the better. The best radiant barrier paints have an emissivity value of around 0.25, while foil based radiant barriers typically have an emissivity from 0.03 to 0.05. In other words the best paint products can only stop about 75% of the radiant heat, while foil products can block up to 95 to 97% of the radiant heat. In fact, to be even be considered as a true "Radiant Barrier" a material is supposed to have an emissivity of 0.1 or less. The paint products fall sort of this mark.
- It is true that over time dust may accumulate on the top surface of the Radiant Barrier when installed on the attic floor. However, the main reason that a radiant barrier works is that Aluminum has a low emissivity value of 0.03 - 0.05. This means that it only emits 3-5% of the heat by radiation to the cold side. Dust accumulation on the top surface of a double sided material has no effect on the emissivity of the lower side. In addition, most of the dust test available were performed on a single sided material with the aluminum side facing up. It is generally accepted that dust is not an issue when radiant barrier is stapled up above the attic space.
- There are some venders which suggest the use radiant barrier instead of regular insulation, but we always recommend using it in conjunction with regular insulation. The reason is that they work to perform different functions. Regular insulation primarily slows down conductive heat transfer, but does not prevent radiant heat from penetrating. Radiant Barrier blocks radiant heat, but not conductive heat transfer. A good system utilizes both radiant barrier and mass insulation to reduce both types of heat gain or loss.
- Most foil products available today are double sided and it doesn't matter which direction you install them. However, if you were to install a single sided product, the shiny side needs to face the airspace. For example the foil side would face down toward the attic space.
- There are now many websites selling radiant barrier products. Be sure to compare the specifications of the different products. We recommend the following online store. If you live near Dallas, TX you can even pick up material at their warehouse.
972.283.0163
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