Radiant Barriers & Attic Efficiency…How Does Your Home Stack Up?
What Is Radiant Barrier?
Radiant Barrier is an aluminum colored, water-based, low emissivity (low-e) coating. When applied to building materials such as plywood, OSB or plasterboard, Radiant Barrier lowers their surface emissivity to 0.25 or lower, thereby blocking over 75% of the radiant heat trying to enter the home. It is classified by ASTM as an Interior Radiation Control Coating (IRCC).
How Does Radiant Barrier Work?
Radiant barrier or radiant heat barrier works by changing the emissivity of the surface where it is applied.
Building products such as wood, brick, and plasterboard have high emissivities (0.7-0.95). When heated, they radiate most of their heat to cooler surfaces by allowing the heat to penetrate the roof into the attic and from the attic into the house. Radiant Barrier lowers their surface emissivity to under 0.23, lessening their ability to radiate heat and therefore letting less heat penetrate the roof into the attic.
Radiant Barrier is designed to be applied to the under-side of the roof deck and any gable ends of a house. Applying a thin, even coat to these surfaces creates an effective radiant heat barrier that will stop over 80% of potential radiant heat transfer into the attic, which in turn, makes your home more energy efficient.
On hot summer days, the sun heats the exterior of the roof. The darker the roof, the greater the heat transferred. This heat will seek the cool interior of the home. The roof heat is emitted as radiant energy from the underside of the untreated roof deck, down to the ceiling insulation. The insulation, if installed correctly and in good condition, will resist a portion of the heat for a time, but will soon transfer heat down into the living space of the home. Think about how hot a well insulated home can get without air-conditioning.
Radiant Barrier can effectively cut the amount of radiant heat entering your attic. Less heat in the attic equals less heat entering the living space. Radiant Barrier works just like shade trees, keeping your home cooler. Radiant Barrier-Ultra will also keep attic mounted HVAC ducts cooler. Cooler ducts means the AC will not need to work as hard when it is running.
Radiant Barrier is a liquid applied, breathable film that will not contribute to moisture retention. Because the film is non-conductive, Radiant Barrier Ultra will not interfere with attic-mounted antenna or with cell phone reception. Radiant Barrier-Ultra has almost no odor to it because it is water based and now has lower VOC’s, therefore, making it environmentally friendly.
Benefits Of Using Radiant Barrier For Your Home
- Lowest emissivity available at 0.19
- Substantially lowers your cooling bills
- You feel cooler, more comfortable in your home
- Ideal for hot climates
- Low cost for long term results! Energy Efficiency!
- Environmentally friendly, very low odor
Where Can Radiant Barrier Be Used To Make Your Home More Energy Efficient.
- Roofs: Building products such as wood, brick, and plasterboard have high emissivities (0.7-0.95). When heated, they radiate most of their heat to cooler surfaces by allowing the heat to penetrate the roof into the attic and from the attic into the house. Radiant Barrier lowers their surface emissivity to under 0.23, lessening their ability to radiate heat and therefore letting less heat penetrate the roof into the attic.
- Radiant Heating Systems: It is an effective heat reflector when used behind wood stoves or on walls adjacent to ceiling mounted radiant heaters in commercial applications.
- Vent-Skin Construction: A vent-skin roofs Radiant Barrier should be applied on the underside of the outer roof skin facing down into the vent channel. On vent-skin sidewalls Radiant Barrier should be applied on the inside of the outer skin facing into the vent channel.
- Sidewalls: Though it can be used on sidewalls, Radiant Barrier is normally more effective when used under roofs. Roof surfaces are generally much hotter than sidewalls. Up to 80% of the summer heat gain is from above. Low surfaces become more effective in controlling radiant heat transfer as the temperature of the radiant heat source increases. However, in tropical climates where no insulation is used in sidewalls, Radiant Barrier can substantially help increase interior comfort.
Frequently Asked Questions About Radiant Barrier
Do Radiant Heat Barriers Lower Heating Costs?
While they are most effective at lowering cooling costs, studies performed by the University of Kansas have showed a 15% reduction in heat loss through the attic when radiant barriers are used.
Does Radiant Barrier Degrade Over Time? What Is The Product Life Span?
Radiant Barrier does not lose its effectiveness over time like some products. Foils can tear and require the staples to penetrate the barrier. Foil chips can accumulate dust, which diminishes their effectiveness. Radiant Barrier will last as long as the surface area it is applied to is not damaged or disturbed and nothing is coming in contact with the product.
Is Attic Ventilation Important?
Absolutely! Radiant heat barriers only control radiant heat loads. Good attic ventilation helps control convection loads. Together they raise the comfort levels and lower cooling costs. Venting to allow 2.5 air changes per hour should be specified as a minimum.
What Is The Recommended Application Method For A Radiant Barrier?
For best results, spray application using a spray pump size 3/4 GPM or greater, 2,000 psi and tip size of 0.017" to 0.021". The product can be rolled with a 3/8" synthetic nap roller, however, roofing nails penetrating the surface can make brushing or rolling difficult.
What Is the Coverage Rate For the Radiant Barrier?
Recommended coverage for Radiant Barrier is 325 - 500 sq.ft. per gallon depending on the porosity of the substrate.
What Is Emissivity?
Emissivity is the ability of a surface to radiate or emit energy in the form of long wave electromagnetic radiation. It is represented by a value from 0 to 1. The closer the value is to 1, the less effective the surface is at impeding radiant heat transfer. Wood has an emissivity of 0.90. Thus, when wood is heated above the temperature of surrounding surfaces, it will tend to transfer 90% of its heat energy by radiation. Radiant Barrier, when applied to most non-porous surfaces, will decrease the surface emissivity to 0.25 or lower, allowing less than 25% of the heat energy to be transferred by radiation.
What Is The Role Of Air Space When Using Radiant Barrier?
To function effectively, a radiant heat barrier must face an airspace of 1" or greater. A radiant heat barrier will not function if sandwiched between two solid surfaces. Radiant Barrier, when installed on the underside of roof decking, normally faces downward into the attic. If insulation is installed in the cavity formed by the roof trusses and roof decking (as in a cathedral ceiling), at least 1" should be allowed between the top of the insulation and the Radiant Barrier surface.
Is The Radiant Barrier Permeable To Water?
Yes! Radiant Barrier allows water vapor to permeate, and does not trap water vapor within roof decks or sidewalls. This is vitally important in attic conditions.
Do Radiant Barriers Have An “R” Rating?
No. R-values apply only to solid insulation or to insulating systems that control heat flows other than radiation. In independent testing of the product at the University of Kansas, the R-value of the insulation, after applying Radiant Barrier-75 to the roof deck, increased by 87% to 98%.