Frequently Asked Questions About Reflective Insulation, Radiant Barriers and Interior Radiation Control Coatings (IRCCs)
What is a radiant barrier? – Radiant barriers function by reducing heat transfer by radiation. The reduction of radiant heat transfer is directly proportional to the surface emittance of the radiant barrier material. Emittance measurements of all materials range between zero (0), no radiant heat transfer, and one (1) that of a black surface or a total radiant heat transfer material. Common building materials such as wood and masonry have surface emittances of approximately 0.85 and therefore have high radiant heat transfer rates. Products defined as radiant barriers have low heat transfer rates with surface emittances less than or equal to 0.1. This results in lower interior surface temperatures because dramatically less radiant energy is being transferred by the radiant barrier to the interior of a building.
Why don’t radiant barriers have an r value? R-values are a performance criteria utilized for determining the comparative thermal performance of mass insulation products (fiberglass, cellulose, foam …). Radiant barriers provide benefits in a different way. They reduce radiant heat gain into a structure resulting in cooler interior surface temperatures and cannot be quantified by an R-value.
How Do Radiant Barriers work? – Radiant barrier system work by reducing radiant heat gain. To be effective, the product must face an air space. Radiant barriers are most efficient during periods of hot weather in which they reduce radiant energy transfer into a structure, resulting in reduced HVAC usage.
What types of radiant barrier are available? – Several types of radiant barrier materials are in the market. Most products available commercially, fall into two major categories:
- Aluminum Foil Laminates – aluminum foil laminated to kraft paper, plastic films, or to OSB/plywood roof sheathing
- Aluminized Plastic Films – a thin layer of aluminum particles deposited on film through a vacuum process
How much do radiant barriers cost? For a new construction project with a standard radiant barrier/OSB product, with a requirement of 1,500 square feet; installation costs on average between $300 and $500. A larger and more complex project can cost anywhere between $600 and $2,000, due to increased labor needs. For the DIYer, a product roll of 500 square feet averages $0.14 to $0.20 per square foot.
Who makes radiant barriers? There are many manufacturers of radiant barriers; but to ensure you receive a quality product, it is recommended that you consider a radiant barrier manufactured by a member of the Reflective Insulation Manufacturers Association International.
Does radiant barrier need an air space? Yes. A “radiant barrier system” (RBS) requires that at least one (reflective) side of the product faces an air space. Most commonly, a ventilated attic provides the air space below a radiant barrier.
Is Radiant Barrier better than mass insulation? – It provides benefit differently than mass insulation. The two product types complement each other. A radiant barrier makes mass insulation more efficient because the summer attic temperatures are lower. This results in less conductive heat transfer for the mass insulation to have to address.
What is the R-value of bubble wrap Reflective Insulation? – Reflective Insulation assembly R-values can range from R-3.0 to R-21 (depending on application). These products have 20+ applications around a typical home. The Reflective Insulation is always installed in conjunction with an enclosed air space. The R-value is determined by the size of the air space and its location within the structure.
Does Radiant Barrier affect WIFI or Cell Signals? – In general, metal can affect the transmission of radio waves, which is what both cell phones and Wi-Fi systems use for communicating information. As most radiant barrier products contain a thin layer of aluminum, there could be a slight impact to these signals, but the impact is expected to be minimal. Cell signals bounce and reflect off a number of surfaces in a home to transfer information between the nearest cell tower. The roof only covers 20-30% of the surface area of a home, and the thickness of the aluminum is only a few microns thick, so the actual impact is probably so slight that you’d be hard pressed to notice it. With Wi-Fi signals, unless the radiant barrier is between you and the router, there is unlikely to be any impact.
Is spray on radiant barrier effective? – These reflective paint products are called Interior Radiation Control Coatings (IRCCs). When the coating is installed correctly, it will block about 75% to 85% of the radiant energy. They perform in the same manner as a radiant barrier.
Will reflective insulation prevent condensation? If so, how?
Yes. Reflective insulation is often an outstanding solution to condensation problems. The thermal break provided by the air space prevents warm, moist air inside a building from interacting with cold air on the other side of the surface. When installed correctly, with secure seams, condensation will be dramatically inhibited or eliminated.
Do I need to tape the seams?
This will be dependent on your application. Refer to the manufacturers’ installation instructions.
Are there places reflective insulation or a radiant barrier can be installed in an existing structure?
Yes, there are many places these products can be installed retrofit. These areas include an attic, HVAC ducting, water heater, basement ceiling, knee wall, garage door, crawl spaces, just to name a few.
Should radiant barrier be installed on gable ends?
Yes. Gable end walls are also an area that allows radiant energy to enter the house. The reflective side of the product should face into the attic space.
Can radiant barrier be installed only on specific portions of the roof?
Although some benefit will be derived by a partial installation, this is not recommended. Your benefit will be proportional to the amount of the roof area in which the product is installed. Full benefit requires a complete envelope of the reflective surface, including gables.
Will radiant barriers damage my shingles?
No, there is a wide range of mechanisms at work which dissipate the heat blocked by the radiant barrier. Studies have shown that shingle temperatures only rise approximately 2-5 degrees F using radiant barriers. This is well within the 200 degree F shingle temperature that most shingle companies warrant.
Can reflective insulation be installed on walls?
Yes it can but, the proper air space must be maintained between the reflective product surface and any other materials. This may require additional construction methods and materials to create the required air space.
Can other materials such as spray foam be installed against radiant barrier in the attic?
No. An air space must exist on the reflective side of the product in order to net reduced radiant energy transfer benefits. Spraying foam over the full surface will totally negate any benefits.
How does an Interior Radiation Control Coating (IRCC)/low emissivity coating work?
An IRCC works by changing the emittance of the surface that is coated. It is a liquid product applied like paint. Building products, such as wood, brick, painted surfaces and plasterboard exhibit high emissivities (0.7 – 0.95). When heated above the temperature of adjacent surfaces, they radiate most of their heat energy to cooler surfaces. IRCCs work by lowering the surface emittance (to between 0.25 to 0.15), thereby reducing their ability to radiate infrared energy. This is the same thermal performance benefit mechanism provided by a radiant barrier.
Why would someone choose an IRCC over a radiant barrier?
An IRCC is normally applied using airless spray equipment, resulting in very low labor costs and greatly reduced installation times. Also, a water based IRCC can be safely installed in existing structures where the costs of installing reflective foil or film products may be prohibitive or impractical. These reflective liquid products may also be used in many manufactured products (such as infrared heat reflectors of automotive parts) where it is impractical to adhere/attach foil or film radiant barriers.
Can reflective paints be used with radiant heat systems?
Yes. Reflective paints are effective heat reflectors when used behind wood stoves or on walls adjacent to ceiling mounted radiant heaters in commercial applications.
Is there a radiant barrier paint on the market?
There has been a lot of talk lately about the benefits of radiant barrier paint. The problem is, according to definitions set forth by the American Society of Testing and Materials International (ASTMI), there is no such product currently available that has a 0.10 or lower emittance performance rating. There are low-emittance or reflective paints, which are also known as Interior Radiation Control Coatings (IRCC) with emittance values in the range of 0.25 to 0.15.