Radiant Barriers 101 - Increase Your Understanding

Radiant barrier foil insulation is a reflective insulation system that offers a permanent way to reduce energy costs. Radiant barrier foil insulation systems BLOCK radiant heat energy instead of absorbing it like fiberglass insulation.  A pure aluminum radiant barrier reflective foil insulation is unaffected by humidity and will continue to perform at a consistent level no matter how humid it may be. A radiant barrier foil insulation system is a layer of foil facing an airspace and is installed in the envelope of a building.

In order to fully understand how radiant barriers work and how they can benefit you, the following information has been comprised to provide a foundation for your new radiant barrier knowledge and understanding.

How Heat is Transferred

Heat is transferred from one source to another via three methods of transfer: conduction, convection, and radiation.

Conductive:  the transfer of heat flowing through a substance (molecular motion) or to another touching substance. If you touch a pot on the stove, the heat is transferred from the pot to your hand via conductive heat transfer.

Convective:  the transfer of heat in fluids, such as rising heated air, steam, and moisture. If you put your hand above a boiling pot, you will feel heat rising from the pot in the form of steam. This transfer of heat from the pot upwards is via convective heat transfer.  Convective heat transfer results in warmer air rising and cooler air settling creating a convection loop termed free convection.  A Convection loop can also be generated mechanically with the aid of fan or wind and is then called forced convection.

Radiant: the transfer of heat via infrared radiation rays that are invisible to the naked eye and unaffected by air currents.  If you step outside on a windy sunny day, you will feel the sun's heat rays on your face. This transfer of heat from a heated source across an air space to a colder surface is via radiant heat transfer.  All materials radiate radiant heat in ranges from 0% to 100%.

Common examples of radiant heat transfer:

• Skin warming up when outside on a sunny day via the radiant heat from the sun regardless of the ambient temperature.

• Roof shingles heated via the radiant heat from the sun.

• Heat radiating from a light bulb.

Convention Insulation

Most people are familiar with traditional insulating materials such as fiberglass, cellulose, Styrofoam, and rock wool.   These products absorb or slow down convective and conductive heat transfers to insulate.  These types of insulation do not BLOCK heat - only slow it down.  Therefore, after a period of time, 100% of the heat absorbed would eventually transfer through the insulation.  The rate in which this heat eventually transfers through an insulation material is the material's R-Value.

• Fiberglass and blown-in cellulose insulation rely on air spaces within the material to decrease the conductivity of heat.  They also reduce convective heat flows by trapping heating air flows and thereby restricting air circulation.

• Foam insulations work similarly to fiberglass and blown-in insulation with the exception of using hydrochlorofluorocarbons (HCF), instead of air, to absorb and slow down the transfer of heat via conductive and convective measures.  However, the United States has scheduled phasing out the manufacturing and importing of all HCFs over the next 23 years.  HCF's, such as those contained in foam insulation products, are considered very potent greenhouse gases.

Conventional insulations do not insulate against radiant heat transfers.

All three methods of heat transference are in play in your home or building year-round.  The following three charts show the percentage of heat transferred via conduction, convection and radiation from each direction of heat flow.   In all cases, radiant heat transfer is the dominant mode.

Conductive    Convective    Radiant       

     

As can be seen, radiant heat transfer is the largest mode of heat transfer within a building structure yet conventional insulations (fiberglass, cellulose, Styrofoam, and rock wool) deal with only conductive and convective heat transfers leaving the radiant heat transfer completely unprotected against.  

How Radiant Barriers Work

A radiant barrier reflects/BLOCKS radiant heat energy instead of trying to absorb it.   A radiant barrier also REDUCES convective heat transfer by acting as a physical blockade against convective air flow.

How does a radiant barrier reflect/BLOCK radiant heat?

The aluminum found in radiant barriers has two properties that enable it to reflect/BLOCK radiant heat:

Reflectivity = The natural reflectivity property of aluminum facing a heat source across an air space allows the aluminum to REFLECT radiant heat back to the direction from which it came. Emissivity = All materials have emissivity's ranging from 0% to 100%.  The lower the emittance percentage of a material, the lower the amount of radiant heat radiated from its surface.  The naturally low emissivity property of aluminum facing an air space results in very low emittance of heat from itself; it does not radiate much of its own heat from itself.    This naturally low emissivity property makes aluminum ideal for use in radiant barriers.

Example of reflectivity property in common every day uses.  This aluminum keeps the chocolate from getting too warm and melting.

As noted above, a radiant barrier will only work when at least one side of it faces an air space (either the side facing the heat source OR the side facing away from the heat source).

The air space MUST be at least 3/4" or more.

Location of air spaces in common radiant barrier installations:

• Laid over the attic floor:  One air space is located above the radiant barrier (the attic air space).  One air space is located underneath the radiant barrier (between floor joists and/or inside of fiberglass or blown-in insulation).

• Stapled to the underside of attic roof rafters:  One air space is located above the radiant barrier between each rafter.  One air space is located underneath the radiant barrier (the attic air space).

• Stapled directly to the underside of the roof decking:  One air space is located underneath the radiant barrier (the attic air space).

• Stapled to exterior as a house wrap:  One air space is located on the outside of the radiant barrier between any exterior surface (siding, brick, etc).  An air space can be created by installing 1X2 furring strips over the top of the radiant barrier to which to attach the exterior surface.

Blocking Radiant Heat Transfers in a Home or Building

All building surfaces include roofs, ceilings, and even conventional fiberglass and blown-in insulation radiate heat in varying degrees.  Radiant heat from the sun strikes the outer surfaces of roofs and walls and is absorbed causing building surfaces to heat up.  This absorbed heat moves through the material (via conduction) to the opposite side and is then radiated from itself into attics and living spaces increasing the temperatures inside the building.

During the winter, 50-75% of heat loss through the ceiling/roofing system and 65-80% of heat loss through walls is radiant. In the summer, up to 93% of heat gain is radiant. If you are depending on R-value (resistance) alone to insulate against heat gain and loss, remember that traditional forms of insulation are virtually transparent to radiant energy and are affected by changes in humidity (moisture levels). A 1-1/2% change in the moisture content of fiberglass insulation will result in a 36% decrease in performance (referenced from HVAC Manual 10.6; McGraw-Hill).

Installing a radiant barrier is a MUST to combat the major form of heat transfer (radiant)  that is currently not being controlled by your conventional insulation.

What Classifies as a Radiant Barrier

Per the Department of Energy (DOE), a product classified as a "radiant barrier" MUST have a low emittance of 10% or less and a high reflectance of 90% or more.

RadiantGUARD® radiant barriers have an emittance of only 3% and a reflectance of 97%; considerable better than the DOE's radiant barrier minimum classification requirements.  For more information, visit the Department of Energy website.

How RadiantGUARD® Radiant Barriers Benefit You

RadiantGUARD® radiant barriers reflect/BLOCK radiant heat; not just absorb or slow it down like other forms of insulation.

RadiantGUARD® radiant barriers are unaffected by humidity or ambient temperatures, unlike other forms of insulation, and therefore, perform at a consistent level at all times.

RadiantGUARD® radiant barriers reflect/BLOCK 97% of the radiant heat transfer and when installed in an attic space, they can result in a reduction of attic temperature below the radiant barrier of up to 30 degrees.  Lowering the temperatures above living space ceilings provides a significant benefit by reducing air conditioning loads and energy usage.  Our radiant barriers can:

• Reduce heat transfer from attic to living spaces by up to 50%,

• Extend the life of air conditioning unit,

• Increase the comfort level of a home or building, and

• Reduce utility bills up to 17%.

RadiantGUARD® radiant barriers are safe and easy to install:

• No breathing apparatus required

• Non-toxic / non-carcinogenic

• Clean and lightweight; easy to handle

• Installation requires no special tools or clothing

• Don't promote the growth of fungi or bacteria

• Provides no nest support for rodent or insect pests

• Class A / Class 1 Fire Rating

• Meets fire and smoke safety requirements of most federal, state and local building codes

• Require no maintenance

• Do not shrink

RadiantGUARD® Testing and Approvals:

• United States Testing Company

• Tennessee Valley Authority

• Tennessee Technological University

• State of California Quality Standards

• Oak Ridge National Laboratory

• Metro Dade County

• Texas A&M University