What Is Radiant Barrier and Why It Works

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 a 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'll offer little benefit, add unneeded labor and price, and cause possible building science–related problems. Here’s the way to decide if they’re right for you.

The Basics

Maintaining a cushty indoor environment may be a building science that goes beyond keeping unwanted heat or cold out and conditioned air in. Although most builders understand the fundamentals of warmth transfer and skills to make homes that are reasonably efficient when it involves heating and cooling, the concept of radiant heat transfer is usually misunderstood or misapplied. As a result, radiant barriers, which are available for years and are a rapidly growing category thanks to increased home energy requirements, aren't employed by many builders.

Inflated, inaccurate, and conflicting claims about the appliance , cost efficiency, and usefulness of radiant barrier products have also hindered their use. In some cases, consistent with 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 facility who has studied radiant barriers within the field and within the lab. “Do radiant barriers work? Yes. Are there other belongings you can do to urge 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 that have introduced new or improved products that, they claim, are thoroughly researched and offer valid benefits at an inexpensive cost. Additionally , several of today’s most progressive green building guidelines, just like the 2010 California Green Building Standards (CALGreen) Code and Energy Star 3, now specify radiant barriers in residential heat-control applications.

One product especially , radiant barrier sheathing, is gaining traction among home builders, including large production builders. consistent with a spokesman for LP Building Products, the manufacturer of TechShield Radiant Barrier OSB sheathing, 87 of the highest 100 builders within the U.S. now use radiant barrier OSB for roof and gable-end sheathing, and one out of 5 homes inbuilt 2010 included radiant barrier sheathing.

KB Home, a national builder based in l. a. , installs TechShield along side other energy-efficient features on most of its homes. TechShield, which was previously sold under the name CoolPly, features a layer of reflective aluminium foil bonded to at least one side of ordinary 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.

According to Dan Bridleman, senior vice chairman for sustainability and technology with KB Home, “We had been using radiant barriers for an extended 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 supply efficiency for homes. Once you begin putting radiant barriers on a roof, you’re watching different R-values.”

Bridleman emphasizes that KB Home doesn't reduce the quantity of insulation it normally installs when radiant barrier sheathing is employed and says radiant barriers are “just one a part of the insulating system.” Because KB Home buys TechShield in volume, he adds, home buyers pay no additional cost for it.

Blocking energy

Radiant barrier products aren't new. As far back because the 1960s, builders and HVAC installers in Sun Belt states have used aluminum-foil sheeting in attics to dam radiant heat gain from sun-warmed roofs. Since that point , liquid radiation control coatings designed to be sprayed, rolled, or brushed onto interior surfaces even have been developed. These barriers help to scale back a number 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 may be a highly reflective material that blocks heat transmitted within the sort of infrared or long-wavelength radiation. Such barriers typically contains a skinny layer of aluminum or metallic foil bonded to a different material that adds strength and sturdiness. Not all shiny foil materials qualify as radiant barriers: to satisfy ASTM C1313 and C1371 specifications, the fabric must reflect up to 90% of warmth radiation and have an emittance rating but 0.1.

Interior radiation control coatings (IRCCs), on the opposite hand, are applied directly onto the inside side of exterior walls and roofs. These coatings offer little or no heat-reflective performance and are instead designed to dam heat that builds up within the materials they're adhered to. The effectiveness of the coating is restricted by the condition of the substrate it's applied to, the thickness and porosity of the coating, and other factors.

To perform properly, radiant barriers must be installed facing an outdoors space. When placed directly against another material, these barriers actually promote heat transfer by conduction, rather than blocking or reflecting it away. Impermeable radiant barriers and coatings also can restrict airflow. Because improper installation can cause moisture buildup and structural damage, perforated and vapor-permeable products are now available to stop those issues.

Radiant barriers aren't insulators and thus haven't any inherent R-value. But when used as a part of an insulating system, like when installed along side batt or foam insulation with appropriate air spaces between each material layer, radiant barriers reduce the warmth emitted into a structure and enable the insulation to perform at or near its intended R-value. Radiant foils bonded to insulating materials, like plastic “bubble wrap,” often claim to possess R-values, but it's the air trapped within the plastic that's doing the insulating, not the foil. However, by repelling a number 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're generally effective and price 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 within the farthest southern U.S. locations can save the maximum amount as $150 per annum on their electrical bills by installing radiant barriers. However, this is often a best-case scenario. The estimated cost savings fall to as little as $5 per annum within the most southerly areas if there are not any HVAC ducts or air handlers during a home’s attic. consistent with ORNL, the speed of savings also drops off quickly for homes in milder climates, with homes in cooler latitudes receiving little or no enjoy radiant barriers.

Similar studies by the Florida solar power Center support this data. Claims of utility savings up to 40% are unrealistic, consistent with the FSEC website. A more credible expectation amounts to savings of three to six 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. During a sampling of product manufacturers, material costs alone for interior radiation control coatings ranged from 20 cents to 55 cents per sq ft of coverage, while radiant barrier products range from 10 cents to 65 cents per sq ft, consistent with FSEC. Installed costs are often up to 3 times higher, supported 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 utilized 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 lots of 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 choice of allowing all that heat into the attic then handling it after the very fact with insulation,” Drew says. “Or, he can add a radiant barrier, which can barricade 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 upper cost of retrofitting foil or liquid radiant barriers distorts the value equation. Installing radiant barrier OSB roof and gable-end sheathing typically adds $300 to $400 in cost to a replacement home, Drew estimates. supported those figures, the three to six annual energy savings cited within the FSEC data, “from a replacement construction standpoint, may be a big number. I’m pleased with 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 satisfy 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 employed by RIMA et al. within the insulation industry, “Any quite performance claim, by law, must be supported by test data.” He recommends that installers search for such verification on product specifications and packaging.

RIMA officials acknowledge that misinformation about radiant barriers and coatings has dogged the industry, but they assert it's not always intentional. “These are some things we fight continuously,” says executive Mary Edmondson, who noted that the organization provides information to support industry claims also as debunk “myths and misconceptions.”

In the end, it's up to the architect, builder, or installer to work out the relative advantages or disadvantages of including radiant barriers or interior radiation control coatings during a home’s insulating envelope.