Radiant Barrier Facts

What is a radiant barrier?

Radiant barriers are materials that are installed in buildings to reduce summer heat gain and winter heat loss, reducing building heating and cooling energy usage and corresponding utility costs. This, results in energy savings and improves the comfort in your home or building.
The largest benefit of attic radiant barriers is primarily in reducing air-conditioning cooling loads in warm or hot climates. Attic temperatures can be reduced by as much as 30 degrees. Since most homes have duct work from the heating and air conditioning systems located in the attic, adding Radiant Barrier can reduce air conditioning demand by as much as 50%.
Radiant barriers usually consist of a thin sheet of highly reflective aluminum, applied to one or both sides of a number of substrate materials. These aluminum layers reflect and reduce the emittance of radiant energy by 97%. The unique multi-layer design of radiant barriers reduce heat gain in the summer and heat loss in the winter. Some products are fiber reinforced to increase the durability and ease of handling. Radiant barriers can be used in residential, commercial, and industrial buildings.

How are radiant barriers installed in a residential attic?

Radiant barriers may be installed in attics in several configurations. The simplest is to lay the radiant barrier directly on top of existing attic insulation, with the reflective side up. This is often called the attic floor application. (shown right)

Another way to install a radiant barrier is to attach it near the roof. The roof application has several variations. One variation is to attach the radiant barrier to the bottom surfaces of the attic truss chords or rafter framing. Another is to drape the radiant barrier over the tops of the rafters before the roof deck is applied. Still another variation is to attach the radiant barrier directly to the underside of the roof deck. All Home Comfort's knowledgeable staff can assist you in choosing the correct application for maximum energy savings and greatly improved comfort.

How do radiant barriers work?

Radiant barriers work by reducing heat transfer by thermal radiation across the air space between the roof deck and the attic floor, where conventional insulation is usually placed. 

On a sunny summer day, solar (Radiant) energy is absorbed by the roof, heating the roof sheathing and causing the underside of the sheathing and the roof framing to radiate heat downward toward the attic. Roof mounted radiant barrier works by reflecting up to 97% of radiant energy, thus reducing attic temperatures and by blocking thermal radiation from striking the top of the conventional attic floor insulation, the insulation surface temperature is lower and the heat flow through the insulation is reduced much more than it would have been without a radiant barrier.
In many buildings the duct work (and some times the equipment) from the heating and/or air conditioning system are located in the attic. In the cooling season, as cold air is passing thru the ducting it can be pre-heated from the surrounding or ambient air temprature in the attic. This means that the work your air conditioner has produced to provide cold air to your rooms is partially lost costing you money in increased utility expense. Radiant barrier can lower hot summer attic temperatures by up to 30 degrees, thus reducing the amount of heat transfer to your air conditioning ducting resulting in improved cooling performance, reduced energy bills, environmental conservation, increased home comfort and reduced operating expenses.

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.

Can Radiant Barrier be used in other applications?

Yes! All Home Comfort offers products that are excellent for use as under floor insulation on raised foundation buildings as well as applications for knee walls (A wall between the attic and vaulted ceiling area of a home.) Radiant barrier is also the preferred choice for metal buildings. Radiant Barrier is often seen in warehouse applications applied to the underside of the roof structure. All Home Comfort's knowledgeable staff can assist you in choosing the best application for your needs.

What are the characteristics of a radiant barrier?

All radiant barriers have at least one reflective (or low emissivity) surface, usually a sheet or coating of aluminum. Some radiant barriers have a reflective surface on both sides. Both types work about equally well, but if a one-sided radiant barrier is used, the reflective surface must face the open air space. For example, if a one-sided radiant barrier is laid on top of the insulation with the reflective side facing down and touching the insulation, the radiant barrier will lose most of its effectiveness in reducing heating and cooling loads.

Emissivity is the property that determines how well a radiant barrier will perform. This property is a number between 0 and 1, with lower numbers indicating better potential for performance. The emissivity of typical, clean, unperforated radiant barriers is about 0.03 to 0.05. Hence they will have a reflectivity of 95 to 97 percent. Some materials may have higher emissivities. It is not always possible to judge the emissivity just by visual appearance. Measured emissivity values should be part of the information provided by the manufacturer.

Radiant Barrier Features and Benefits: