radiant barrier insulation is energy conservation

Frequently Asked Questions

about Radiant Barrier




                              

  • What is radiant barrier?
  • The name comes from the ability to be a barrier to the transfer of radiant heat. Radiant barrier is made from materials that are very good at reflecting radiant heat and the ability to reduce the emission radiant heat.
  • What is radiant heat?
  • Radiant heat is heat that is radiated from a heat source through space (with or without air). The heat you feel from a hot griddle on the stove is radiant heat. Most of the heat from a bright light bulb is radiant heat. Radiant heat is also called infra-red heat or infra-red energy.
  • What is infra-red energy?
  • Infra-red energy is electro-magnetic energy that is not visible. It is next to red in the wavelength spectrum.  It travels at the speed of light until it hits an object. When infra-red energy is traveling through air, a very small portion of the energy is absorbed by molecules in the air.
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  • How does heat move?
  • Heat moves by conduction, convection, and radiation.
  • Conduction is the process that occurs in substances denser than air like water and wood and stone where the heat moves through the substance. Conduction occurs rapidly in metals like gold and copper and very slowly in an insulation like fiberglass.
  • Convection is the process where air makes contact with substances that are conducting heat and the air is heated. Hot air rises and this movement makes room for cooler air and the process continues until the air and the surfaces are close to the same temperature
  • Radiation is the process of the infra-red energy emitting from the heated substance through space. The energy travels in a straight line at the speed of light until it is absorbed or reflected by another substance. It is important to remember that in order for heat to move by radiation, there must be space between the objects. The space can be as small as a few air molecules and still be effective. If the objects are touching, then the heat moves by conduction, not be radiation.
  • What is reflectivity?
  • Reflectivity, for radiant barrier purposes, can be defined as a measure of how much of the energy is reflected and not absorbed by the barrier. Very shiny aluminized plastic can reflect 98% of the radiant heat that strikes it.
  • What is absorbtivity?
  • Absorbtivity, for radiant barrier purposes, can be defined as a measure of how much of the energy is not reflected and is absorbed by the material.
  • What is emissivity? Emissivity, for radiant barrier purposes, can be defined as a measure of how much of the absorbed energy is emitted by the barrier. Very shiny aluminized plastic only emits about 3% of the heat absorbed radiantly and also from the hot air around it.
  • What is emissivity?  (black bumper/chrome bumper)
  • Which is hotter in the sun when left in the parking lot for several hours:
  • 1) A black bumper
  • 2) A Chrome bumber
  • Everything above absolute zero has thermal energy.  The farther (hotter), something gets from absolute zero, the faster it radiates.  The ability or amount of radiated infrared energy is greatly affected by the surface of the enitity.  Smooth, shiney surfaces tend to be reflective but have a very low emissivity value which tends to trap the heat inside.  Like chrome tools in your toolbox when you leave the lid open in the sun, a chrome door handle, the ignition switch in your car.
  • The ability for a chrome surface to emit radiant heat is around 4%.  What about the black bumper?  Most paints emit in the .92 range regardless of color.  Try to separate the "black is hotter" mental image from the ability of the surface to release or emit radiant heat.
  • The black bumper will get hotter faster (easily absorbs radiant heat), but as the temperature rises so will the rate at which  infrared heat is emmitted.
  • The chrome bumper being chrome will reflect most of the radiant heat.  However, due to the low emissivity, the heat is trapped and the surface temperature rises.
  • What kind of materials are used to make radiant barrier?
  • Aluminum foils are one common material. Our proprietary products use a new type of plastic radiant barrier made possible by successful research into making a lighter weight radiant barrier for spacecraft. The process is called vacuum deposition technology and it makes it possible to put a very thin deposit of metal on a film substrate.
  • After the summer sun goes down, where is the hottest place in the attic?
  • The top couple of inches of the insulation!  And it remains the hottest place in the attic until the next morning when the sun begins its radiant heating again.  It is easy to comprehend when we consider that the insulation has been absorbing radiant heat all day long, and now it is resisting that heat is trying to leave into the cooler attic air and radiating to the cool roof decking.
  • Where is the best place to install radiant barrier in the attic?
  • One problematic technique is to put radiant barrier directly on the underside of the roof sheeting. What happens in any attic that is not extremely well ventilated is that the surface of the radiant barrier gets very hot and the heat is then  convected into the air of the attic causing the attic and its insulation to get quite hot.  This is only true in an attic with a pitched roof.  Flat roof homes can really benefit from a RBS attached to the bottom.
  • To see the results of RBS testing on four indentical, unoccupied homes, click here.

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    Another location is on top of the insulation. Here, the radiant barrier does the bulk of its work by preventing the infra-red energy from being absorbed by the porous insulation.  However, laying a single layer of a reflective surface makes the RBS vulnerable to the inevitable settling of dust on the surface.  This application begins degrading from the day it is installed and continues until it is completey covered and severly degrades performance.   This is why the RBS Chips works so well and carries a lifetime, transferable performance warranty.
     

  • How important is attic ventilation with an attic radiant barrier system?
  • Ventilation is very important because this is the primary method used to get rid of the heat that is being reflected by the radiant barrier.  In climates that require a lot of cooling, it is recommended that attic ventilation at the top of the attic meet or exceed the Uniform Building Code recommendations of 1/150th of the attic area. The UBC also specifies 1/600th at the eaves/soffits of the roof. It is recommended that this be at least 1/200th of the attic area. The UBC's attic ventilation requirements are directed toward preventing moisture condensation problems but they are equally valuable to hot climate homes that need to get rid of the heat absorbed by the roof.
  • Sheets of radiant barrier are very difficult to install in existing attics. It is also difficult to get a good installation because of the difficult working conditions of extreme heat in the summer, low headroom, numerous roof framing or truss webs in the way, and low light conditions.
  • What is the "Achilles Heel" of radiant barrier?   
  •   Dust., water and contact with other surfaces.  Dust accumulation will degrade performance over time.  This is one reason our RBS Chips are patentable over other RBS.  RBS Chips are impervious to dust.  Most RBS are comprised of aluminum which can corrode rapidly when in contact with water for extended periods.  RBS in dircect contact with any surface negates performance as radiant heat cannot be reflected or emitted, only conducted.

  • Is there a way to avoid dust in attics?
  • No. There is no practical way to keep an attic dust free so the challenge for radiant barriers is to work well in spite of the dust. As a matter of fact, a radiant barrier system is not designed to work with dust is not worth considering. Some studies seem to be finding that some types of dusty radiant barrier are worse than no radiant barrier at all.
  • Well, then if the attic floor is the best place for radiant barrier but dust makes it not work, and it is difficult to install, what are my options?
  • These challenges were the catalyst to the invention of a new kind of radiant barrier called EcoGuard Radiant Barrier Chips (click here) .  Chips are made from aluminized plastic film that is then blown over the existing insulation.  To install it, a small blower and hose is employed to blow a coating of chips on top of the existing insulation. The radiant barrier becomes a topcoat to the insulation, the "icing on the cake" that makes a complete insulation.

    • Dust is no longer the death-knell because the chips are installed multiple layers deep, usually about 10 layers of protection. The layer exposed to dust becomes ineffective on the dusty side but all the rest keep doing their job.
     

  • How about mixing the chips with the insulation?
  • Radiant barrier must have space between it and other materials or it doesn't work. Radiant heat travels through this space and without space, the heat is just conducted from the radiant barrier to the material touching it. The RBS Chip has a patented shape which overcomes these anomalies.
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  • What happens if the chips are disturbed?
  • If the chips are installed on batt insulation, it is very easy to just move them back over the places where the insulation is exposed. When chips are installed on loose-fill insulation and the chips become well mixed with the insulation, it is necessary to thin out the many layers around the disturbed area and use them to cover the exposed insulation. One very good aspect of radiant barrier is that only the area that is not covered is adversely affected. All the rest of the areas continue to perform at the normal level. This characteristic is unlike insulation where if the batt was too small for the cavity it was installed in., it allows great convective air flow and almost makes the insulation useless.

  • Do the chips cause condensation problems?
  • No.  Because the chips are not one continuous layer but are loose, the moisture trying to leave a warm humid house into a cold attic has no problem getting out. But with continuous sheeting radiant barriers, moisture condensation has been a real problem.

  • What if the attic is small and there is no way a person could get in there to blow the chips?
  • Many times such attics are under-ventilated. With the need for more ventilation, this provides a serendipitous opportunity to cut some small holes in the roof, blow the chips in and then install the attic dormer-shaped vents.

  • How about chips and cold climates?
  • Radiant Barrier Chips work even better in cold climates as it does in hot climates. Much like a Thermos bottle, the reflective coating on the RBS film reflects interior heat back into the room. Our testing has shown ceiling temperatures increase 8f to 10f degrees where the chips are installed.  We get reports of 30%-40% savings in heating costs and most customers report they have to turn down the temperature on the thermostat to maintain comfort.

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    Radiant Barrier Chips are safe and non-toxic                Install this product yourself.  Just ask how!



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