Six experts — Lorraine Bittles, associate OSB product manager, LP; J.P. Bolton, vice president of sales, Innovative Insulation Inc.; Wes Hall, national sales manager, Reflectix Inc.; Marcus Jablonka, vice president, research, development, and production, Cosella-Dorken Products Inc.; Bill Lippy, senior vice president, chief marketing officer, Fi-Foil Co. Inc.; and Ryan McCoy, product manager, radiant barrier division, Insulation Solutions Inc. — discuss the state of radiant barriers:

We've been writing about radiant barriers for 20 years, but the principles of the technology can be difficult to understand. How do they work?

Bittles: Radiant barriers minimize heat gain in the summer and heat loss in the winter. A benefit of reducing radiant heat in attics is the immediate reduction in air conditioner cooling loads in warm and hot climates. A radiant barrier is a thin sheet of aluminum that is typically laminated to a substrate material. Because of the aluminum's low emittance, radiant heat is blocked from entering the attic space in hot weather climates. In cold weather climates, because of the aluminum's high reflectance, radiant heat is unable to escape through the roofing materials and is sent back into the home.

Bolton: Radiant barriers outperform standard mass insulation materials due to their physics on control of heat transfer principals. Mass insulation products (I include all fiber and foam materials) delay and accumulate heat, but after the R-value period of time has passed, they become saturated and transmit 100 percent of the heat. R-value is the time period to saturation. Radiant barriers block 97 percent of the heat, and regardless of time period only 3 percent of the heat is ever transferred. Additionally, once saturated, R-value materials are just as resistant to heat dissipation as they are to heat accumulation. To quote Monty Milspaugh, a brilliant mind in the barrier industry, mass insulation is like a sponge with water dripping on it (water equaling BTU's of heat). It absorbs it until it finally becomes saturated, and then every drop of water on the top creates an equal drop of water on the bottom. When the water is turned off, the saturated sponge continues to drip until it dries out.

Jablonka: Have you ever experienced the difference of wearing a black or a white T-shirt on a hot summer day? You will feel cooler when wearing a white T-shirt compared with wearing a black T-shirt. This effect is due to solar radiation, also called electromagnetic waves emitted by the sun (in simple words: a huge amount of energy). Radiant barriers work simply by reflecting as much of the solar energy as possible.

McCoy: Heat can be transferred from the exterior to the interior (or vice versa) of a building in three ways: conduction, convection, and radiation. While most mass insulations try to reduce conductive and convective heat transfer through walls, floors, and ceilings, radiant barriers aim at combating heat transfer that occurs via radiation. Radiation takes place when a warm object or surface begins emitting heat, such as a hot roof radiating downward into the attic in the summertime. The infrared rays emitted by the warm object are absorbed by most common building materials, such as wood and mass insulation, resulting in an increase in the ambient air temperature. Radiant barriers are manufactured with low-e surfaces that allow them to reflect (instead of absorb) radiant heat. When a radiant barrier is installed facing an air space, it redirects heat back to its source, reducing the amount of heat transfer that occurs though the wall, floor, or ceiling.

Is there a point where an insulator stops adding extra insulation and goes with a radiant barrier instead?

Bittles: Installing insulation alone will fall short of maximizing the home's energy efficiency. Best building practices depict that a home should be insulated to code regulations, then followed up with adding a radiant barrier. Both insulation and radiant barriers reduce heat transfer into the house but do so in different ways. A radiant barrier will reduce radiant heat transfer by blocking the sun's heat from entering into the home, whereas insulation will trap still air to reduce conductive heat from entering the living space. Adding a radiant barrier will allow the insulation to perform more efficiently.

Bolton: When a radiant barrier is applied with ancillary mass insulation materials, it blocks 97 percent of the heat and the mass insulator is only subject to 3 percent of the heat load. As a result the addition of more mass insulation is money spent to control 3 percent of the heat and as such is a disutility.

Hall: In keeping your home cooler, mass insulation reduces the conductive heat transfer, ventilation (roof vents or turbines) addresses the convective element, and radiant barriers reduce radiant heat transfer. The most efficient attic system comprises all three types of products: mass insulation, roof vents or turbines and radiant barriers (to address all three modes of heat transfer). If a home is insulated with mass insulation at or less than the code requirement for that region, a radiant barrier is a good choice to provide an additional heat transfer reduction benefit. If a home is heavily overinsulated with mass insulation, the positive effects of the radiant barrier are diminished (but still evident).

Jablonka: Highly reflective roof coverings have demonstrated energy savings in warm, moderate, and cool climate zones. However, their effectiveness in saving energy is highest in warm areas that require cooling throughout most of the year. Reflective barriers should not be used as a tradeoff to reduce the amount of insulation. They work on a different heat transfer mechanism. To achieve the highest energy efficiency of an assembly, radiant barriers and thermal insulation should be used in combination. It is recommended to always use at least the minimum amount of thermal insulation required by the local building code, or better, the minimum amount of thermal insulation recommended by the American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE) 90.1-2007.

McCoy: Radiant barriers are very effective in redirecting heat transfer that occurs via radiation. Therefore, if the insulator knows that there will be a heat source nearby that will be giving off heat, for example a hot roof or in-floor radiant heating tubing, then it makes sense to incorporate a radiant barrier into the system. To provide year-round energy efficiency, the ideal insulation system would include mass insulation and a radiant barrier.

Do radiant barriers qualify for Leadership in Energy and Environmental Design (LEED) credits?

Bittles: Radiant barriers are a major part of green building programs and are certified by various green building standards. Since green building programs tend to be unique to certain regions, homeowners should check with local builders or specifiers to see what the qualifications are in their area.

Bolton: Unfortunately my knowledge of precise LEED certification is limited. I can, however, respond to a similar point system — green points. To gain green points for a structure, an application must be made with the development department of that municipal code entity. We supplied a contractor in Boulder, Colo., with radiant barrier for a project in which the development department required a detailed application for green points specific to this construction. The application was complex and required detailed explanation of how materials could meet certain criteria to be eligible for green points. For example, use of reclaimed lumber earned five points, use of recycled roofing materials gained three points, etc. Radiant barrier applications gained 39 points for the following uses: natural cooling (five points), vapor permeable infiltration barrier (two), radon mitigation (five), innovative product or design (10), energy code measures (17). The result was 39 points earned for the green program.

Jablonka: Under the United States Green Building Council (USGBC) LEED program, one point can be granted for the installation of a reflective roof membrane. Thus the use of radiant barriers helps to achieve LEED certification.

Lippy: Generally the largest impact from adding a radiant barrier would be under energy and atmosphere and optimizing energy performance. The radiant barrier will assist in achieving increasing levels of energy performance above the baseline to reduce environmental and economic impacts associated with excessive energy use. Note that the actual points awarded for a radiant barrier will depend on the energy software program selected. Under materials and resources, radiant barriers can help you gain points for building and materials reuse, and regional materials points may also apply, depending on the manufacturer's location in reference to the building site. Finally, under indoor environmental quality, radiant barriers do not emit fumes, particles or other toxins and help improve thermal comfort design.

McCoy: Because radiant barriers save energy and increase building comfort, they line up directly with the goals and values of the LEED program, which are centered on creating sustainable, energy efficient structures. Radiant barriers can earn LEED points for a project by reducing the amount of energy needed to heat or cool a building and sometimes even allowing the designer to specify smaller heating, ventilating, and air conditioning (HVAC) equipment. Radiant barriers also can earn points in the area of IAQ (indoor air quality) because they do not emit chemicals or fibers.

In what regions and markets are you seeing the most growth?

Bittles: The demand for radiant barriers has increased over the past few years as buyers have become increasingly conscious of the environment and energy cost saving. According to KB Homes, one of every two homebuyers chooses to purchase a radiant barrier in markets where our product is available. In some Sunbelt markets, that rate is 80 percent. Radiant barriers were first created and used in the hot Texas market, and now we are seeing the demand for the product spanning into other regions that are affected by the summer heat.

Bolton: The main area where we are seeing an exponential increase in acceptance is the architectural field. The architects are at the top of the food chain in this business. If they spec it, it is going into the project. The main hindrance in the past has been the lack of exposure to radiant barrier products. That has changed. The next hurdle was the misconception that since a radiant barrier only affects radiant heat and has no effect on conductive or convective heat transfer that it is ineffective as an insulation material. The error in this otherwise valid assumption is that heat transitions through all three transfer phases when entering or exiting any structure. The architects who understand this aspect of the radiant barrier materials create a huge benefit to the owner. Also the green movement is definitely an area where radiant barriers outperform the mass insulation products.

McCoy: There seems to be a growing interest among architects and builders regarding how they can incorporate radiant barriers into their homes and buildings. In years past, the interest seemed to be coming mostly from homeowners and do-it-yourselfers. We speculate that the demand for green and sustainable buildings is driving architects and builders to seek out ways to differentiate their work in today's competitive market.