Radiant Barrier Questions: (Click a question to reveal the answer)
Technical questions
- What is a radiant barrier?
- A radiant barrier is a highly reflective insulation material designed to resist heat transfer across an air space. The material must have a low emissivity (0.10 or less) and a high reflectivity (90% or greater). Radiant barriers are most commonly used in attic spaces to lower radiant heat gained or lost through the ceiling.
- How does radiant barrier work in an attic?
- Radiant heat travels through space (vacuum, air or any gas) and is either absorbed or reflected by the first solid object that it encounters.
In the summer, heat from the roof decking typically radiates down through the attic and is absorbed by the insulation heating up the house below. Installing a radiant barrier between the roof and the insulation reflects the heat back out, greatly reduces the amount of heat absorbed into the house.
In the winter, heat from the house typically radiates off the insulation into the attic space and is absorbed into the roof decking to be lost outside. Installing a radiant barrier between the insulation and the roof reflects the heat back into the house below, reducing the amount of energy required to heat the house.
- Why are air spaces required for ARMA FOIL™ to work?
- A radiant barrier only works on radiant heat. In order for radiant heat transfer to occur there must be a gap (air space) between two objects of different temperatures. If there is no gap (air space), there is no radiant heat. The heat would move from one to the other by means of conduction. Radiant barriers only work on radiant heat, they do little to reduce conductive heat transfer.
- What is the R-Value of radiant barrier?
- 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. We do not generally assign an R-Value to ARMA FOIL™ as it is greatly dependent on the installation method and any R-Values are associated with a whole assembly. It is ARMA FOIL's™ low emissivity and ability to reduce radiant heat that makes it such an energy saver.
There are, however, R-Values associated with the air spaces in a building assembly. The R-Value of an air space depends heavily on the emissivity of adjacent materials, the size/orientation of the air space and the direction of the heat flow. For example, if we consider a 3.5" air space enclosed by wood or any other common building material and assume the heat is flowing in the downward direction, its R-Value is increased from 1.22 to 8.17 by adding a single layer of ARMA FOIL™ above the air space. While the radiant barrier technically has no R-Value, in this case it adds nearly R-7 to the whole assembly.
- Is your perforated radiant barrier as effective as the non-perforated version?
- Yes it is, the perforations are small and do not lower the performance of the material in any measurable way. They are designed as small as possible to allow the material to "breathe" (let moisture out) and have virtually no effect on the overall thermal performance.
- Is double-sided radiant barrier any better than the single-sided type?
- Yes, but only if it is installed with an air space on both sides. There are two properties which allow radiant barriers to work, reflectivity and low emissivity (low-e). Regardless of the season and directing of heat flow, the heat is both reflected back towards its source on the hot side and not re-emitted to the air on the cold side. Of these two properties the low-e value is of greater importance. According to a study performed by a Texas A&M University professor, double-sided radiant barriers were nearly 50% more effective than their single-sided counterparts.
- Why does ARMA FOIL™ only have a reflectivity of 95% when some of the other products claim 97%? Do they work better than ARMA FOIL™?
- While untreated aluminum has an emissivity as low as 0.03 reflecting up to 97% of the radiant heat, it quickly degrades as a clear layer of oxidation builds on the surface. In fact, some heavily oxidized aluminum alloys have an emissivity as high as 0.4 and would only reflect about 60% of the radiant heat.
ARMA FOIL™ comes pre-coated with a special coating to prevent oxidation from occuring. While this coating does slightly increase the emissivity to 0.05, ARMA FOIL™ will continue to reflect 95% of the radiant heat for years to come.
- How does Radiant Barrier Foil compare to the paint products?
- The most important specification to look at when comparing different types of radiant barrier is the emissivity value. The best radiant barrier paints have an emissivity value of around 0.16, while ARMA FOIL™ radiant barrier has an emissivity of 0.05. The lower this value, the better it works at blocking and reflecting heat. In other words, the best paint products can only stop about 84% of the radiant heat, while our foil products can block up to 95% of the radiant heat. In fact, to even be considered as a true "Radiant Barrier", a material must have an emissivity of .1 or less. The paint products fall sort of this mark. Compare Foil vs Paint
- Will radiant barrier prevent my cell phone from working or interfere with radio reception?
- A foil radiant barrier can slightly lower reception for radio based electronics. Most of the time this interferance is insignificant and will only pose a problem if your reception is extremely poor to begin with. We have tested a cell phone and found that we had to completely wrap it in 14 layers before it stopped ringing. We have sold radiant barrier for over 10 years suppling over 25,000 homes and in this time we have talked to less than 5 customers with this complaint. All of them admitted to having poor reception even before the radiant barrier was installed.
If this is a consern, you may consider using a radiant barrier paint product which has no effect on radio signals.
- Is ARMA FOIL™ as strong as some of the other heavier weight radiant barriers?
- ARMA FOIL™ is a lighter weight material that actually resists tearing better than every other code complient radiant barrier on the market. Some companies boast heavier and thicker materials as if that translates into a higher tear strength. New technologies have allowed us to produce lighter weight yet stronger materials. For example, a titanium or carbon fiber mountain bike is much stronger than its steel counterpart even though it is half the weight.
Here is the difference. Our competition makes radiant barrier by laminating sheets of foil/film to a plastic lining. In order to make it stick, they must heat the plastic to its melting temperature. Heat treating plastic in this way makes it brittle and more suseptable to tearing from a staple. To test for this, take a sample of both products, snip into the side with a pair of siscors and then try to tear it. Metalized film and PE based laminated products will continue to tear easily. Since ARMA FOIL™ is not laminated, it never undergoes the heat cycle resulting in a much stronger product at a lower physical weight. Lighter weight material is both easier to work with and less expensive to ship saving both time and money.
- What makes ARMA FOIL™ better than other radiant barriers?
- We believe ARMA FOIL™ is the best material on the market. It is non-laminated, protected against oxidation, lighter weight yet stronger, passes all current codes, and is easier to install. For more details and information read "What makes ARMA FOIL™ the best radiant barrier available?"
Installation related questions
- How much savings can I expect after installing radiant barrier in my attic?
- Your actual savings will vary with many factors including: attic installation method, house shading, duct leakage, air handler location, geographic location, etc. In the summer, you can see a huge reduction in heat gained through the ceiling, translating into a savings of up to 30% on cooling bills. In the winter, radiant barriers reflect heat back towards the house reducing heat loss and increasing overall savings.
- Can I use a radiant barrier instead of regular insulation?
- While there are some vendors which suggest using radiant barrier instead of other insulations, we always recommend using it in conjunction with regular insulation. The reason is that they each work to perform different functions. Regular insulation primarily slows down conductive heat transfer, but does not prevent radiant heat from penetrating. Radiant barrier works primarily to block radiant heat. A good system utilizes both radiant barrier and mass insulation to reduce both types of heat gain or loss.
Please read our "Radiant Barrier vs. Fiberglass Insulation" article for more information on this topic.
- Should I use perforated or non-perforated radiant barrier in my installation?
- It depends on your particular climate and application. If you are installing the Radiant Barrier on the outside/exterior of mass insulation, you generally want to use the perforated type so as not to trap moisture within the wall. If your climate or local codes call for an interior vapor barrier, you can install the non-perforated type on the inside/interior of your mass insulation. In this case you would also tape the seams to create a vapor barrier.
We recommend only using perforated radiant barrier in all attic installations.
- How much tape do I need?
- When using ARMAFOIL-VB™ or ARMAFOIL™ in an air barrier application, it is important to seal all the seams. You will need approximately 1 roll of our foil tape (2" x 150') for every 1,000 sq ft of radiant barrier.
- When stapling radiant barrier up under my roof, does it matter which side faces down?
- All of our radiant barrier materials are double-sided (foil on both sides), so it will not make any difference in which side faces up or down. However, if you were to install a single-sided product, the foil side should face down towards the attic space.
- Are soffit and ridge vents required for Radiant Barrier to work?
- While attic ventilation plays an important role in relieving moisture and excessive heat build-up, it is not a requirement for radiant barrier to work. Radiant barrier will reflect the same amount of radiant heat even in an attic with no ventilation.
- How much of a space should I leave at the eave and ridge?
- We recommend leaving a mininum gap of at least 2" between the foil and the insulation at the eaves. This allows ventilation air from the soffits to flow both above and below the foil. We recommend leaving a minimum gap of at least 2" inches at the ridge.
Please note: some states like California recommend a 5" gap at both the top and bottom
- Will radiant barrier help if my attic is already well ventilated?
- Yes, as a matter of fact very little radiant heat is captured by air and removed by attic ventilation. Radiant heat travels in the form of waves through space until it is either absorbed or reflected by a solid surface. So even in a well ventilated attic, without radiant barrier installed, your home will still suffer from excessive radiant heat gain.
Think about standing outside on a bright sunny day. You will get just as sun-burned on a windy day as you would on a calm day. The wind does not prevent the solar radiation from hitting your skin. In a similar way, attic ventilation may help cool your attic space, but it does not prevent radiant heat from penetrating your ceiling.
- Will radiant barrier make my roof hotter and cook my shingles?
- Radiant barriers increase roof surface temperatures by less than 5°F. 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.
more information on shingle temperatures
- I'm having a new roof put on, can I install ARMA FOIL™ between tar paper and asphalt shingles?
- We get this question several times a week, in part because there is at least one website recommending this type of installation. Unfortunately, without the required air space adjacent to the foil surface, the heat will simply conduct through the foil.
There are a few types of roof systems utilizing purlins that do create air spaces and allow ARMA FOIL™ to work effectively.
- Does ARMA FOIL™ meet the requirements of Title 24 in the state of California?
- Yes it does. Title 24 requires that a radiant barrier be at least 95% reflective and strong enough to hold staples when installed above the attic space. ARMA FOIL™ meets both of those qualifications.
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