We are dedicated to teaching people about radiant barrier and the simple science behind it. Radiant barrier is a great product, and as if oftentimes the case with a wonderful thing, there are unfortunately many misconceptions about what radiant barrier is and what it can/cannot do.
Here are the most common myths and misconceptions about radiant barrier foil insulation:
Myth: Adding a radiant barrier below the roof line inside the attic will make the roof hotter and damage the roofing materials, including shingles.
There is a common thought that because radiant barrier reflects 97% of heat back toward the source, it will increase your roof temperature substantially and cause damage to the roof decking and shingles. However radiant barrier doesn't change the amount of heat going through your roof, it simply changes the direction of the heat flow.
Understanding Radiant Heat
Radiant heat by definition is heat that travels as radiation in waves across either a void (air gap) or vacuum until it is either absorbed or reflected. Radiant heat is the INVISIBLE part of the light spectrum; it travels at the speed of light until it is either absorbed or reflected.
A simple way to understand this is to think of a light bulb in a dark room. When you turn the light on, it shines in all directions across the air space in the room – lighting up the space.
The same is happening in your attic; radiant heat from the sun travels across the atmosphere where it then is absorbed by your roof. The heat travels via conduction though the roofing materials and then re-radiates across your attic space, in all directions until it is absorbed or reflected by the items in your attic.
What Happens When Radiant Barrier Reflects Heat
Heat is coming in to your roof - period. Right now, without a radiant barrier, that heat is hitting the roof and being absorbed into the attic. Then it radiates across the attic until the items in your attic, such as your insulation, an A/C unit, duct work, etc., absorb it. When you add the radiant barrier the same amount of heat is still coming in, the difference is that it is not heating up the contents of the attic since the heat is blocked at the roof line (for a staple-up method). So the amount of heat in/on your roof is essentially the same, but now it is being redirected to stay between the foil and the roof, instead of being directed in various directions all over the attic.
Let's revisit the lamp analogy from above. If you take the reflector (lampshade) off the lamp, light goes in all directions (this is how your roof is without a radiant barrier). Once you add the reflector, you redirect the light to mainly go downward, from the bulb. The amount of light the lamp puts off did not change by adding a reflector, you redirected the light to a concentrated area. Do the things in the current path of the light get brighter? Maybe ever so slightly, but it's not as though they have doubled in brightness. The same is true in your attic. The heat that was radiating in all direction is now only radiating upward, away from the attic, instead of upward and downward. This means there is a slight increase in temperature, but the amount is so trivial that it doesn't really have an impact on the overall temperature of the roof or the shingle life.
Measured Temperature Differences
The government, privately owned companies, RIMA and even AtticFoil.com have all done studies to test the measurable temperature differences in a roof with radiant barrier versus a roof without radiant barrier. Some of these studies go back 20 years or more, but they all have the same conclusions. All testing concludes that the temperature of a roof does not increase enough to warrant concern about shingle life or roofing damage.
The average roof temperature increase in the studies ranged from 2°F - 10°F. On roofs with darker shingles, the temperatures overall were measured higher than on roofs with lighter shingles, as was to be expected. One example of a roof we measured showed that without radiant barrier the temperature was 166°F -167°F (this was for a medium/dark shingled roof). On the area that did have radiant barrier installed the readings were 173°F - 174°F. The tests conclude an increase of about 6°F to 7°F degrees in roofs with a radiant barrier installed below the shingle line. This is exactly within the parameters found by major studies done on the effect of radiant barrier on roof temperatures, proving that radiant barrier only increases the shingle/roof temperature by a nominal amount. This small increase is considered negligible and not having any sort of negative impact on either shingle or roofing material life.
Shingle Warranty and Radiant Barrier
Many people often wonder if installing a radiant barrier will void their shingle warranty. While it's best to check with the manufacturer of your specific shingles to see what guidelines are in place for your particular warranty, oftentimes shingles are made to handle a much hotter load than they do – even with radiant barrier installed. Also, some cities and counties require a radiant barrier on all new homes constructed. If you are unsure about your particular roof, check your paperwork before installing a radiant barrier. Remember, on a 100°F day, with a roof getting up to 180°F – a temperature increase within 10°F is nominal in the overall assembly. Make sure you install the radiant barrier with the proper air gaps, have adequate and uninterrupted air flow in the attic and start reaping the benefits of a radiant barrier today.
For more information on RIMA's testing of roof shingle temperatures, click here.
Myth: Using a radiant barrier causes moisture problems that ultimately lead to mold and mildew.
Did you know that over 70% of all home issues are moisture related? Moisture problems are not always complicated to solve, but that doesn't mean they can't pose big problems. To be proactive toward these potential problems, it's important to keep your attic both cool and dry.
Condensation is simply water changing its form. You have a gas (water vapor) changing into liquid form (water). Water vapor is water that is basically suspended in the air. Condensation occurs when relatively warm-moist air comes in contact with a colder surface. An example of this is someone breathing on a cold window. Warm water vapor in your breath comes in contact with the cold glass and condenses (or converts) into the liquid form of water. So, foil does not cause moisture, warm-moist air and cold surfaces meeting together causes moisture. The key to avoiding moisture problems in your home is to eliminate the source of moisture – or warm-moist air.
Most Common Trouble Spots - HOLES in your ceiling
What are the sources of moisture? Light fixtures, ceiling fans, bathroom fans, and duct registers are the best places to start. Can-lights or recessed lights are usually the worst culprits of air leakage, which carry warm moist air into the attic. If you live in an area that has consistently cold temperatures, it is imperative that you find these sources of air leakage and fix them immediately since prolonged cold temperatures can increase your chances of moisture occurring. You should take care of any of these problems before you think about installing radiant barrier, to make sure you're setting yourself up for optimum results with minimum problems.
So how do you protect yourself against these problem areas? The good news is that many of the moisture culprits can be easily addressed and economically fixed. Air sealing and good attic ventilation all go a long way in helping reduce the probability of moisture causing complications.
The first, and best, method is to seal up all the holes in your ceiling. In fact, you should do this even if you're not installing radiant barrier. Sealing up leaky holes reduces the amount of air leaking out of your home, and ultimately reduces your energy costs. Sealing includes ductwork, HVAC registers, vents and any light fixtures that may not be sealed up completely; an easy way to tell if your lights are sealed is to turn on the lights that share the same drywall as the attic floor, then go up into the attic without turning on the light and look for areas the light is shining through. If you see light – that's a sure fire way to tell the fixture is not airtight. However, just because there is no light coming through a ceiling penetration does NOT necessarily mean the hole is airtight.
Next, make sure than any vents from the inside of the home are vented upward past the insulation, and ideally out of the attic. Vents from kitchens, bathrooms or laundry rooms should all be routed so that they vent to the outside, not into the attic. If you have any vents that are currently blowing into the attic, they need to be re-routed before you install a radiant barrier.
Finally, proper ventilation in an attic is essential to creating a dry space. The idea behind ventilation is quite simple – don't over complicate it. You need intake vents and exhaust vents; intake should occur at the bottom of the attic and exhaust vents should occur at the top since this is in line with natural airflow (warm air will naturally rise). Typically your intake vents will be your soffit vents. Make sure these vents are clean and clear of obstructions (insulation, paint on the screens or built up dust or dirt. etc.) so that they are functioning properly. Exhaust vents can range from gable vents and ridge vents to attic fans of all types. Again, ventilation is simple; you need to create an easy way for air to come in the attic and an easy way for it to leave the attic. This natural flow allows for moisture to freely move about and eventually diffuse. Incidentally, this is why radiant barrier is perforated and why you should always use a perforated product in a vented attic. The perforations in the foil are tiny pinholes that allow water vapor molecules to pass through. In an attic situation this is exactly what you want: moisture moving freely to contribute to an overall dry attic space.
Dealing with Moisture Build Up
As a preventative measure, it is recommended that if you are installing a radiant barrier and you are not 100% sure that the obstacles underneath it are airtight, it is best to play it safe and cut holes in the radiant barrier foil insulation above those areas. Ideally you want full coverage, but a little bit of foil cut out over a large install area is not going to dramatically alter your results or the effectiveness of the product.
So what if you are dealing with a moisture problem that already exists? Well the most important thing is to try to locate the source of the problem. Once you have determined where the moisture is occurring, you should be able to establish what is causing the problem. The best thing to do would be to remove any and all materials surrounding the source until you have remedied the situation. In many cases, it's best to contact a professional when you are dealing with mold, mildew & rot since not every area that is effected will present the same characteristics.
While moisture has the potential to cause severe problems if untreated, do not let it scare you off from doing home improvements. Understand what you are dealing with, eliminate situations that can cause problems and make sure the space you are working in has adequate airflow and ventilation. Taking these precautions will allow your radiant barrier foil installation to go smoothly and it will set you up to receive the best-case results from the product. Remember: radiant barrier alone doesn't cause moisture, but it can disclose areas where air is leaking from your home.
Myth: The accumulation of dust on radiant barrier compromises it's reflectivity and therefore its ability to work as a reflector of radiant heat.
To begin, it's truthful to say that most homes will not accumulate enough dust in the attic area to diminish aluminum's reflective quality. Even at a glance, a thin layer of dust on your AtticFoil® radiant barrier has been shown to cause no difference in the ability of the material to reflect radiant heat. A simple way to think of this is to consider a mirror in your home that might get dusty; the more dust that accumulates, the more reflectivity the mirror will lose.
Dust and Single-Sided Foil
Before double-sided foil was created, radiant barrier existed as a single-sided product. Because of this, installation was precise in which side of the foil needed to face up or down. About 30 years ago, when single-sided foil still dominated the market, most installations consisted of laying the foil on the attic floor, over the existing insulation. The foil was installed with the foil side facing up, leaving it prone to dust collection. In cases where dust accumulated rapidly and frequently, it was noted that this had an impact on the reflectivity of the radiant barrier. Large amounts of dust can reduce, or eliminate, aluminum's ability to act as a reflector of radiant heat. Therefore, it was determined that when using a single-sided product, careful measures had to be taken in order to minimize dust accrual. Some of these measures included stapling the foil up on the rafters and using multiple layers of foil on the floor, but eventually the superior idea of creating a double-sided material was born.
Dust and Double-Sided Foil
The creation of a double-sided radiant barrier proved to be an economical way to increase year-round benefits, while eliminating the threat of dust endangering the reflectivity of the foil's surface. The main advantages of double-sided heavyweight radiant barrier foil are that it allows for protection against radiant heat by one of two ways: reflectivity or emissivity. Both properties are present in the foil, so if/when one is compromised, the foil can still work off the other property, without a decrease in overall performance.
Reflectivity and Emissivity
Reflectivity is defined as a measure of the ability of a surface to reflect radiation (or energy/heat). Aluminum's reflectivity is 97%; therefore, aluminum has the ability to reflect 97% of the radiant heat waves coming in contact with it. This is why AtticFoil® radiant barrier works so well against radiant heat – when the sun radiates heat to the earth, it is either absorbed or reflected. Typically your roof will absorb the heat (because the majority of roofs are not reflective) and it will travel through the roofing materials until it reaches your attic. At that point there is nothing left to come in contact with so the heat converts from traveling conductively (through materials that are touching in the roof) to its radiant form (heat traveling across an air space) where it can now be reflected (via the radiant barrier) back towards the direction it came from.
Emissivity is defined as the ability of a surface to emit (release) radiant energy. While aluminum has a high reflectivity (97%), it has a low emissivity (only 3%). This means that aluminum only allows 3% of radiant heat to pass through it by means of trapping 97% of the radiant heat behind the foil.
Therefore, depending on which side of the double-sided product the air gap is one, the foil will be either using reflectivity to reflect heat or emissivity to block it. Either way, your results are going to be 97% rejection of heat transfer.
Dealing with Dust
So what do reflectivity and emissivity have to do with dust and how it affects foil? Where previously foil had one side, optimal conditions were required in order to make sure the topside would not be compromised by dust accrual. Now, with double-sided foil, even if the dust does get to a point where it jeopardizes the reflectivity, the foil on the bottom side (the side facing the insulation on the floor) will work off of it's emissivity quality, only allowing 3% of the heat to pass through.
If it's wintertime and you're heating your home, this means you're not losing heat through the roof and so you home stays warmer without using as much energy (to replace what is being constantly lost). If it's summertime, this means only 3% of the radiant heat entering your attic will be emitted into the insulation on your floor. So rather than absorbing 100% of the heat and having to run your air conditioner to keep your living space cool, you now only have to deal with about 3% of that heat. That means a cooler, more comfortable home and a more reasonable energy bill. Overall double-sided foil is the best choice for all applications of a radiant barrier because it offers you the advantage of both of aluminum's properties, making dust a non-issue.
Myth: If I install a radiant barrier on my roof my cell phone won't get reception in my home because the aluminum blocks the radio waves.
Radio waves and cell phones.
Cell phones use radio waves to transmit signals, including the ones that allow us to make phone calls, send text messages and stream the web. Radio waves control more than just phone signals; they control the signals for TV, cordless phones, garage door openers, microwaves and even your wireless routers.
What materials block radio waves?
There are several materials that have virtually no effect on radio waves. Those materials include plastic, glass and wood. On the other hand, there are materials that will block radio waves, many of them being metallic in nature. Aluminum is one of those materials known to block radio waves.
Aluminum and Cell Phones
The thickness and the amount of the aluminum being used (surface area) can determine whether or not it will completely block radio waves to/from your cell phone. Consider certain buildings where your cell phone doesn't work, this could include hospitals, research facilities and government buildings. Typically these buildings are forged with thick, metallic frames and walls, making signal transmission in and out of the building difficult without specific technology.
A different example is your car. You most likely have no problems transmitting signals to/from your cell phone while in your car (though the occasional dropped call can happen, this has nothing to do with the car's metallic exterior). Your car, unlike a building, has a much thinner metallic structure and it contains about 40% glass, making transmissions easier.
AtticFoil® and Cell Phones
AtticFoil® radiant barrier, like the car example, is a thin layer and is only covering the roof of your home (generally around 20-35% of your total surface area). Your home still has four walls that radio waves can travel seamlessly through to provide a signal for your cell phone. Both the thickness and the amount of foil being used make it unlikely that it will have any impact on your cell phone. Additionally, many new phones are equipped to handle commonplace interferences because they are made with stronger antennas. The only cases where we've heard of signal transmission problems arising are where the cell phone or particular area had a weak signal to start with, beyond that there have been no reported issues.
The Final Proof
In general, installing a radiant barrier in your attic (or on your roof) will not affect your cell phone's signal. If you still have concerns that your phone can't handle the interference, we recommend you order a FREE sample of our radiant barrier foil from us so you can test it yourself.
Simply lay the phone down on a flat surface and set the sample of AtticFoil® radiant barrier on top of the phone. Then, from another phone, call the phone under the foil. If the phone doesn't ring, then it might have some trouble with getting a signal after installing a radiant barrier in the attic. Two ways to remedy this are to use your phone near the perimeter of the house (near outside walls versus interior rooms), or you can install an external antenna to help boost the signal.
If your phone does ring, then it should have no trouble handling the addition of a radiant barrier to your home.
Bottom line: usually installing a radiant barrier does not cause any problems with cell phone reception. However, if you already have a weak signal, then installing a radiant barrier may push it to the point that you may have some reception issues.