Radiant barriers are recommended by many of today’s green building rating systems and emerging codes. When properly specified and installed, these products function as part of a structure’s insulating envelope. However, research shows that they perform better and contribute more toward comfort and savings in some climate zones than others; and when used incorrectly, they may offer little benefit, add unneeded labor and cost, and lead to possible building science–related problems. Here’s how to decide if they’re right for you.
Maintaining a comfortable indoor environment is a building science that goes beyond keeping unwanted heat or cold out and conditioned air in. Although most builders understand the basics of heat transfer and know how to create homes that are reasonably efficient when it comes to heating and cooling, the concept of radiant heat transfer is frequently misunderstood or misapplied. As a result, radiant barriers, which have been available for years and are a rapidly growing category due to increased home energy requirements, are not used by many builders.
Inflated, inaccurate, and conflicting claims about the application, cost efficiency, and usefulness of radiant barrier products have also hindered their use. In some cases, according to building-science researchers and even industry proponents, this has given these products a negative image and resulted in confusion among green building professionals. “There’s nothing wrong with the products themselves,” says Craig Drumheller, a building product specialist at the NAHB Research Center who has studied radiant barriers in the field and in the lab. “Do radiant barriers work? Yes. Are there other things you can do to get more benefit at less cost? Probably. There are better ways to spend your money on energy savings.”
This view is challenged by radiant barrier manufacturers, especially those who have introduced new or improved products that, they claim, have been thoroughly researched and offer valid benefits at a reasonable cost. In addition, several of today’s most progressive green building guidelines, like the 2010 California Green Building Standards (CALGreen) Code and Energy Star 3, now specify radiant barriers in residential heat-control applications.
One product in particular, radiant barrier sheathing, is gaining traction among home builders, including large production builders. According to a spokesman for LP Building Products, the manufacturer of TechShield Radiant Barrier OSB sheathing, 87 of the top 100 builders in the U.S. now use radiant barrier OSB for roof and gable-end sheathing, and one out of five homes built in 2010 included radiant barrier sheathing.
KB Home, a national builder based in Los Angeles, installs TechShield along with other energy-efficient features on almost all of its homes. TechShield, which was previously sold under the name CoolPly, has a layer of reflective aluminum foil bonded to one side of standard oriented strand board. When installed foil-side down, the roof deck itself prevents a measurable amount of solar heat gain from migrating into a home’s interior spaces. This one-step process enables builders to install both a radiant barrier and roof sheathing in one cost-efficient operation.
According to Dan Bridleman, senior vice president for sustainability and technology with KB Home, “We had been using radiant barriers for a long time, especially in high-heat areas like Texas. We worked with LP and identified that, from an energy perspective, this product would keep heat out and provide efficiency for homes. Once you start putting radiant barriers on a roof, you’re looking at different R-values.”
Bridleman emphasizes that KB Home does not reduce the amount of insulation it normally installs when radiant barrier sheathing is used and says radiant barriers are “just one part of the insulating system.” Because KB Home buys TechShield in volume, he adds, home buyers pay no additional cost for it. In areas where high solar heat is not a factor, the company decides whether to install radiant barrier sheathing “on a case-by-case basis.”
Blocking Radiant Energy
Radiant barrier products are not new. As far back as the 1960s, builders and HVAC installers in Sun Belt states have used aluminum-foil sheeting in attics to block radiant heat gain from sun-warmed roofs. Since that time, liquid radiation control coatings designed to be sprayed, rolled, or brushed onto interior surfaces also have been developed. These barriers help to reduce some of a home’s heat load—and associated energy costs—and are particularly effective when cooling equipment is installed in unconditioned attic spaces.
A radiant barrier is a highly reflective material that blocks heat transmitted in the form of infrared or long-wavelength radiation. Such barriers typically consist of a thin layer of aluminum or metallic foil bonded to another material that adds strength and durability. Not all shiny foil materials qualify as radiant barriers: To meet ASTM C1313 and C1371 specifications, the material must reflect up to 90% of heat radiation and have an emittance rating less than 0.1. Emittance is a ratio of energy or heat that is intercepted by the barrier and reradiated outward.
Interior radiation control coatings (IRCCs), on the other hand, are applied directly onto the interior side of exterior walls and roofs. These coatings offer little or no heat-reflective performance and are instead designed to block heat that builds up within the materials they are adhered to. The effectiveness of the coating is limited by the condition of the substrate it is applied to, the thickness and porosity of the coating, and other factors. To meet ASTM C1321 standards, IRCCs must have an emittance rating less than 0.25.
To perform properly, radiant barriers must be installed facing an open air space. When placed directly against another material, these barriers actually promote heat transfer by conduction, instead of blocking or reflecting it away. Impermeable radiant barriers and coatings can also restrict airflow. Because improper installation can lead to moisture buildup and structural damage, perforated and vapor-permeable products are now available to prevent those issues.
Radiant barriers are not insulators and therefore have no inherent R-value. But when used as part of an insulating system, such as when installed along with batt or foam insulation with appropriate air spaces between each material layer, radiant barriers reduce the heat emitted into a structure and enable the insulation to perform at or near its intended R-value. Radiant foils bonded to insulating materials, such as plastic “bubble wrap,” often claim to have R-values, but it is the air trapped in the plastic that is doing the insulating, not the foil. However, by repelling some of the radiant heat-energy, the foil is contributing to the insulation’s effectiveness.
Green Building Value
Controversy has surrounded radiant barrier products since their introduction. Advocates say they are generally effective and worth the installation and material cost. Skeptics claim the barriers provide scant benefit and are only effective in limited, high-heat climatic areas—and even then deliver a poor return on investment.
Studies by the Oak Ridge National Laboratory show that homeowners with attic HVAC systems in the farthest southern U.S. locations can save as much as $150 per year on their electrical bills by installing radiant barriers. However, this is a best-case scenario. The estimated cost savings fall to as little as $5 per year in the most southerly areas if there are no HVAC ducts or air handlers in a home’s attic. According to ORNL, the rate of savings also drops off quickly for homes in milder climates, with homes in cooler latitudes receiving little or no benefit from radiant barriers.
Similar studies by the Florida Solar Energy Center support this data. Claims of utility savings up to 40% are unrealistic, according to the FSEC website. A more credible expectation amounts to savings of 3% to 6% on “the entire annual electricity bill” for a typical Florida home (DOE Climate Zone 5).
By these measures, the installed costs for radiant barriers and coatings can outweigh their return-on-investment for homeowners and builders, leading many experts to question their value. In a random sampling of product manufacturers, material costs alone for interior radiation control coatings ranged from 20 cents to 55 cents per square foot of coverage, while radiant barrier products range from 10 cents to 65 cents per square foot, according to FSEC. Installed costs can be up to three times higher, based on industry averages, and retrofit costs often higher.
However, other studies support the contention that radiant barriers can contribute to energy savings. One industry-funded test on OSB with radiant barrier foil installed over R-30 insulation demonstrated that, during simulated hot summer conditions, combined air-conditioning energy savings up to 30% are attainable. And a 2010 ASHRAE study conducted by ORNL concluded that, when used in combination with various other insulation and energy-saving construction design strategies, “radiant barriers showed excellent performance in hot climates.” Neither study evaluated the effectiveness of radiant barriers alone.
David Drew, an LP Building Products manager for TechShield OSB, says the ASHRAE tests confirmed that radiant barriers not only helped to save on cooling costs in hot climate zones but also contributed to peak-load energy savings in cool-climate regions as far north as North Carolina. “The builder has the option of allowing all that heat into the attic and then dealing with it after the fact with insulation,” Drew says. “Or, he can add a radiant barrier, which will block up to 96% of that radiant heat and reduce attic temperatures by 30%.”
Drew says a homeowner’s return on investment improves when a radiant barrier is installed during new construction. He says the higher cost of retrofitting foil or liquid radiant barriers distorts the cost equation. Installing radiant barrier OSB roof and gable-end sheathing typically adds $300 to $400 in cost to a new home, Drew estimates. Based on those figures, the 3% to 6% annual energy savings cited in the FSEC data, “from a new construction standpoint, is a big number. I’m proud of that number,” he says.
Choosing Radiant Barriers
Products that claim to be radiant barriers or interior radiation control coatings must pass third-party testing to meet building and energy code requirements, as determined under ASTM standards. RIMA International, the Reflective Insulation Manufacturers Association, verifies compliance and lists products that have met the test criteria.
According to David Yarbrough of R&D Services, an independent testing facility used by RIMA and others in the insulation industry, “Any kind of performance claim, by law, must be supported by test data.” He recommends that installers look for such verification on product specifications and packaging.
RIMA officials acknowledge that misinformation about radiant barriers and coatings has dogged the industry, but they say it is not always intentional. “This is something we fight continuously,” says executive director Mary Edmondson, who noted that the organization provides information to support industry claims as well as debunk “myths and misconceptions.”
In the end, it is up to the architect, builder, or installer to determine the relative advantages or disadvantages of including radiant barriers or interior radiation control coatings in a home’s insulating envelope.
Reflectix. Reflective Insulation consists of two layers of 5/16-inch-thick polyethylene “bubble wrap” with a reflective foil layer bonded to one or both exterior faces. It helps to reduce heat loss by reflecting away up to 96% of radiant energy, while air trapped in the bubbles blocks conductive heat transfer with R-values up to 4.55. Flexible and versatile, it can be installed in most building applications to block heat loss or gain around ductwork, water heaters, and pipes. It meets fire, smoke, and building code requirements, as verified by RIMA International, and is Energy Star qualified for residential applications. 800.879.3645. www.reflectixinc.com. Circle 360.
Ainsworth. Thermastrand OSB roof sheathing has a micro-perforated, low-emission aluminum foil facing bonded to its surface during manufacturing, which helps to reduce or eliminate panel warping and foil bubbling. It blocks up to 97% of the sun’s radiant heat and offers a 25-year warranty against delamination. This product is certified to meet Sustainable Forestry Initiative (SFI) requirements, meets California’s Title 24 energy efficiency code, and is Energy Star qualified. 877.661.3200. www.thermastrand.com. Circle 364.
Dow Building Solutions. Tuff-R Insulation has a polyisocyanurate foam core with radiant barrier-quality aluminum foil facers adhered to both sides. One side of standard Tuff-R is reinforced with kraft paper under the foil facing; Super Tuff-R includes a triple ply of polyester, kraft paper, and reinforced foil for increased durability. Available in several thicknesses and nominal 4x8-, 4x9-, and 4x10-foot sheet sizes, both types can be applied to a variety of substrates. They are Energy Star qualified and meet IBC/IRC requirements for foam plastic insulation. 866.583.2583. www.insulateyourhome.com. Circle 362.
Innovative Energy. AstroECO is an aluminum foil-faced polyethylene bubble film made from 25% recycled materials. Its thin design profile (1/16- or 2/16-inch) makes it easy to handle and install, yet it provides R-values up to 9.3 when installed as specified, as well as reflectivity ratings to 96% and emittance to 0.05. The product’s specifications are verified by RIMA International, and it is Energy Star qualified. 800.776.3645. www.insul.net. Circle 365.
Norbord. Solarbord Radiant Barrier Sheathing has heat-reflecting foil laminated to oriented strand board, so it installs like standard sheathings without additional labor and blocks up to 97% of solar radiant heat. It carries a 25-year warranty, is Energy Star and SFI certified, and is a NAHB Research Center Green Approved product. 888.667.2673. www.solarbordosb.com. Circle 361.
Georgia-Pacific. Thermostat radiant barrier sheathing is available in SFI-certified plywood and OSB panels for roof and gable-wall sheathing. The Energy Star-rated sheathing blocks up to 97% of solar radiant heat, carries a limited-lifetime warranty, and can contribute towards NGBS (NAHB Green Approved), LEED, and EarthCraft Home certifications. 800.284.5347. www.gp.com. Circle 363.
LP Building Products. TechShield Radiant Barrier installs like conventional oriented strand board (OSB) roof sheathing but is manufactured with aluminum foil laminated to APA Exposure 1 rated sheathing. Energy Star qualified, it uses wood that meets Sustainable Forestry Initiative standards and contains no urea-formaldehyde, so it can help contribute to green building credits. It also features a patented incising process that allows construction moisture to dry quickly. It is available in nominal 4x8-foot sheets and a variety of performance categories (thicknesses). 888.820.0325. www.lpcorp.com. Circle 366.
SOLEC Solar Energy Corp. New Lo/Mit MAX Radiant Barrier Coating offers an emittance rating of 0.147, as verified by RIMA International, and meets all applicable code standards. This qualifies as the most efficient performance available for this type of product, according to the manufacturer. This silicone-based, waterborne liquid has a Class A flame-spread and smoke rating and low VOCs, and comes premixed. It can be applied to most building surface materials with a roller, brush, or standard low-pressure air or airless spray equipment. 609.883.7700. www.solec.org. Circle 368.
TVM Building Products. Ultra NT Radiant Barrier is a “metalized” single-layer polyethylene sheet that is guaranteed against delamination. Available as a perforated or solid sheet, it reflects 95% of radiant heat with less than 0.05 emittance, and its thermal performance is not affected by moisture. This product has been verified by RIMA International to meet all applicable code standards. 888.699.1645. www.tvmi.com. Circle 367.