Radiant Barrier

A radiant barrier is an insulation system that utilizes a reflective type of foil-like sheeting that is made of a mixture of highly engineered plastic, metal and in heavier-duty applications fiber threads for added strength.  It serves as an insulator of a type that BLOCKS radiant heat energy, opposed to conventional mass insulations that work by absorbing heat energy.  In order to fully understand how radiant barriers work and how reflective insulation can greatly benefit you, the following information has been provided for your knowledge. 

How is heat transferred?

To best understand how a radiant barrier works we must first understand the different ways thatheat is transferred. There are three ways in which heat is transferred from warm spaces to cold spaces:

Conductive:  the transfer of heat flowing through a solid or fluid material
Convective:  the transfer of heat which involves the physical movement of air when it is warmed 
Radiant:  the movement of invisible heat rays from a warm surface to a cooler surface through an air space

How is reflective insulation different from conventional insulation?

Reflective insulation works differently from conventional insulation products such as fiberglass insulation, cellulose insulation and foam insulation. These products work by slowing down or resisting heat energy. The rate of resistance gives an insulation material it’s r-value. These types of insulation do not block heat energy they only slow it down.  How does a radiant barrier differ from conventional attic insulation?  Radiant barriers perform a function that is similar to that of conventional insulation, in that they reduce the amount of heat that is transferred from the attic into the house. They differ in the way they reduce the heat flow. A radiant barrier reduces the amount of heat radiated across an air space that is adjacent to the radiant barrier. The primary function of conventional insulation is to trap still air within the insulation, and hence reduce heat transfer by air movement (convection).
 
Remember, traditional attic insulation has R-value. This works to slow conductive heat (convection). Radiant barriers reflect Radiant Heat (radiation).  BOTH types of heat are trying to enter your home on a hot, summer day. The sun heats up the roof and then heat is transferred by radiant heat until it hits the attic insulation.  Then, heat switches form to conductive heat to move through the attic insulation and into your home.  This is why you need BOTH Types. Traditional attic insulation and radiant barrier work together and each do their part.
 
Conventional insulations are usually rated by their R-value. Since the performance of radiant barriers depends on many variables, R-value ratings do not apply for them.  Conventional insulations alone do not insulate against RADIANT heat transfer.
 
Radiant heat that is transferred in your home or building enters or escapes in three directions of HEAT FLOW. The charts below show the rate of HEAT GAIN or HEAT LOSS in each instance.
The charts show that radiant heat transfer is responsible for the largest amount of heat loss or gain in a building structure. Considering the fact that fiberglass, cellulose and Styrofoam only guard against heat conduction and convection, we can then understand how much energy is lost or gained through this critical “third side” of the energy transfer pyramid: radiance. 

What classifies as a radiant barrier?

According to the U.S. Department of Energy, for a product to be classified by the government for matters of measuring or providing incentives (tax, development or otherwise) as a RADIANT BARRIER it must have an emission of 10% or less and a reflectance of 90% or more.
 
A radiant barrier utilizes a foil-like surface to reflect radiant heat rays back toward the source.  Its surface has two properties that enable it to reflect radiant heat energy: 
 
  1. Reflectivity - to bend back; to give a backward turn to; to throw back; especially, to cause to return after striking upon any surface; as, a mirror reflects rays of light. 
  2. Emissivity - amount of heat which is "emitted" or radiated off of a surface to the surrounding air.

Our recommended radiant barrier sheeting products have an emission level of just 3% and a reflectance of nearly 97% --- well-exceeding US-DOE minimum classification requirements.
 
For a radiant barrier to work properly the reflective side must face an open air space of at least 3/4”.  Below are some common places a radiant barrier would be installed…
  • Over the top of an attic floor.  
  • On the underside of the rafters in an attic.
  • Around the exterior of a house as a house wrap.
If you are interested in learning more about installing a radiant barrier for your home or for questions, contact us today, we look forward to hearing from you!