Attic Insulation using Radiant Barrier Reflective Insulation

Attic Insulation using Radiant Barrier Reflective Insulation

Contents

The latest advance in attic insulation in recent years by far is reflective aluminum insulation used as a radiant barrier. Radiant insulation reflects heat instead of either absorbing it or letting it pass through. The concept is simple: each unit of radiant heat energy that is reflected away from your home in summer and each unit reflected back inside during winter means less operation of your air conditioning and heating systems, less wear and tear on your equipment, and less money you pay in utility costs.

Radiant insulation is a commercial spin-off of the Apollo space program technology for insulating spacecraft. NASA uses reflective aluminum to effectively block the flow of heat in both directions. It keeps out the intense heat of the sun which, in space, can reach 250 °F and also keeps needed heat inside at night which, in space, can drop to 400 °F below zero.

NASA also uses radiant insulation in space suits, protecting astronauts during space walks. In a space suit, the radiant barrier reflects the astronauts' body heat back to them for warmth. At the same time, the radiant insulation reflects the sun's heat away, keeping them cool. NASA documents report that "Using conventional insulation, a space suit would have required a 7-foot-thick protective layer." Reflective insulation brings this radiant barrier technology to buildings of all types.

Using a radiant barrier in your attic is key to making your home more comfortable, keeping you cooler in summer and warmer in winter. A properly installed radiant barrier in your attic will lower your air conditioning and heating bills and potentially extend the life of your appliances. It is an absolute must in warmer climates. The aluminum foil material commonly used in reflective insulation will reduce radiant heat transfer through your attic by as much as 97%. As aluminum foil insulation is not affected by moisture, it can often completely replace older insulation materials. It can also be used effectively in conjunction with other insulation materials.

Installation in the attic ceiling means that the heat of the sun will be reflected back out of your attic instead of crossing the attic airspace to be absorbed by the attic floor insulation and then down into your house. A 2001 field monitoring study conducted for Florida Power Corporation on the performance of attic radiant barrier systems in central Florida homes found that an attic radiant barrier could save 8-12 % on annual air-conditioning costs. The average cooling energy savings from a radiant barrier attic retrofit was roughly 9% while the average reduction in summer afternoon peak demand was about 16%. The study reported an average 8 degree drop in the average maximum daily summer attic temperature. The U.S Department of Energy Attic Radiant Barrier Fact Sheet (DOE/CE-0335P) states that the cost of cooling can be reduced by up to 17% with proper installation of an attic radiant barrier.

According to whole house tests run by the Mineral Insulation Manufacturers Association and the Oak Ridge National Laboratory, the average reductions in ceiling heat flow due to the addition of a radiant barrier stapled under rafters were between 24 - 30% in comparison with R-19 attic floor insulation and no attic radiant barrier.

Technical data from the Florida Solar Energy Center (FSEC) have shown that in attics with R-19 attic floor insulation plus radiant barriers can reduce summer ceiling heat gains by 16 to 42% compared to an attic with the same insulation level and no attic radiant barrier. The Florida Solar Energy Center says, "If you shop carefully, you will probably find that attic radiant barriers are one of the least costly and yet most effective of the attic conservation measures for Southern climates."

Radiant Installation

Radiant barrier insulation is both easy to install and very affordable. It can be incorporated into new building construction on top of the rafters before adding the roof decking or on the bottom of the roof truss chords or rafters. For existing homes, the radiant barrier can be easily added to your attic by attaching it to the bottom of the roof trusses. Note that the reflective side of the insulation must face the airspace of the attic.

Where to Install Attic Insulation

Reflective insulation is the most effective when incorporated with at least a 3/4" airspace between the insulation and any adjacent material. Many people use furring strips to create additional airspace. Reflective insulation can rest against some other insulations like fiberglass batt and still maintain ample airspace as the batt is composed primarily of airspace. You may also install drywall directly over reflective insulation. Reflective insulation attaches with tape, glue, nails or staples. Note that tape doesn't attach well to concrete or wood. All seams should be sealed with reflective tape.

A note about high moisture content homes - A radiant barrier is not recommended for use stapled over existing attic floor insulation in high humidity areas as it can act as a vapor barrier causing condensation underneath. Condensation can lead to wet fiberglass that loses its insulating abilities and wood rot. Using a radiant barrier over fiberglass insulation in drier areas is acceptable as long as the area is not dusty. Dust that settles on the radiant barrier will reduce or eliminate its effectiveness over time.

Comprehensive attic installation methods and homeowner examples are available by clicking here.

Determine the right product for your attic

Insulation is rated in terms of thermal resistance, called R-value, which indicates the resistance to heat flow. The higher the R-value, the more effective the insulation. Although a radiant barrier reduces heat loss and gain through the building envelope because it is installed in vented cavities (like attics), it is not an insulation material per se and has no inherent R-value. Reflective insulation products incorporate trapped air spaces as part of the system and will carry an R-value. Reflective insulation traps air with layers of aluminum, foam, plastic bubbles, or paper as opposed to mass insulation which uses fibers of glass, particles of foam, or ground up paper.

As an example, compare these two products:

Radiant Barrier: Foil-Foil is two layers of foil held together by woven polypropylene. While an excellent radiant barrier for stapling over or under the rafters or on top of the attic floor insulation, it provides no resistance to heat flow and has no R-value.

Reflective Insulation: : Prodex Total Insulation is a double sided Foil-Foam-Foil construction with two layers of reflective foil encasing 1/4-inch closed-cell polyethylene foam (superior to bubble) to create a true insulating material impeding the flow of warm air. The aluminum is creased to create more airflow in applications, which enhances the insulation performance. The double sided foil construction is the radiant barrier.

Unaffected by moisture, it is preferable to fiberglass batt for multiple reasons. Foil-Foam-Foil insulation can be used alone or as supplemental insulation. You can use polystyrene boards, blown-in, fiberglass batt or other insulations to supplement and achieve the desired R-value.”

DOE Recommended R-values for Wood Frame Homes with Natural Gas Heat and Electric Cooling - Select Cities
	Attic - New	Attic - Retrofit
Bowling Green, KY	49	38
Chicago, IL	49	38
Dallas, TX	49	38
Denver, CO	38	38
Las Vegas, NV	49	38
Los Angeles, CA	22	19
Miami, FL	38	38
Omaha, NE	49	38
New York, NY	49	38
Seattle, WA	38	38

You can determine the correct R-value for your attic based on the type of fuel you use and your zip code using the Department of Energy's R-Value Recommendation form.

Attic Insulation using Reflective insulation is a top priority for reducing energy costs.

Conclusion

According to the US DOE, inadequate insulation and air leakage are the leading causes of energy waste in most homes. The DOE Insulation Fact Sheet lists attic insulation to the recommended R-value as the top insulation priority. "It is most important to:

Insulate your attic to the recommended level, including the attic door, or hatch cover.
Provide the recommended level of insulation under floors above unheated spaces, around walls in a heated basement or unventilated crawl space, and on the edges of slabs-on-grade.
Use the recommended levels of insulation for exterior walls for new house construction. When remodeling or re-siding your house, consider using the levels recommended for new construction in your existing walls."

Key references

Oak Ridge National Laboratory
Radiant Barrier Attic Fact Sheet
http://www.ornl.gov/sci/roofs+walls/radiant/index.html

NASA Scientific and Technical Information
HEATING AND COOLING EFFICIENCY FOR HOMES
http://www.sti.nasa.gov/tto/Spinoff2004/ch_6.html

US Department of Energy
Insulation Fact Sheet
www.ornl.gov/sci/roofs+walls/insulation/ins_01.html

Florida Solar Energy Center.
Radiant barriers: a question and answer primer.
http://www.fsec.ucf.edu/en/publications/html/FSEC-EN-15/index.htm

Space Foundation News, Jan. 14, 2005, Space Foundation certifies Eagle Shield as a space technology improving life in earthly homes

Parker, D.S., J. R. Sherwin and M. T. Anello, January 2001. "FPC Residential Monitoring Project: New Technology Development - Radiant Barrier Pilot Project," Contract Report FSEC-CR-1231-01, Florida Solar Energy Center, Cocoa, Florida.

Reflective Insulation Manufacturer's Association
Understanding and using Reflective Insulation, Radiant Barriers And Radiation Control Coatings
May 2002
www.rima.net

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