A radiant barrier, which most people call attic foil, is aluminum foil on a paper or plastic backing that reflects the heat radiating down from a hot roof. It helps in summer, has no R-value of its own, and pays off mainly in hot, sunny climates with air conditioning ducts in the attic. For a house in New Jersey, Connecticut, the Hudson Valley or Long Island, the Department of Energy’s own guidance points the money elsewhere: in cool climates, adding insulation is usually more cost-effective.
The order for a Northeast attic is air sealing, then insulation to code depth, then, only if the upstairs still overheats and the roof deck is being replaced anyway, foil-faced sheathing. Never foil laid on top of the insulation.
What is a radiant barrier, and what is attic foil?
The Department of Energy describes a radiant barrier as a highly reflective material, usually aluminum foil, applied to kraft paper, plastic film, cardboard, oriented strand board or air infiltration barrier material. The 2024 International Energy Conservation Code, adopted in New Jersey and New York, defines it by one number: a surface emittance of 0.1 or less. “Attic foil” is the everyday name for the same product. AtticFoil, written as one word, is also the brand name of a company that sells radiant barrier rolls online, and nothing here is about any one brand.
- Foil sheet in rolls, single- or double-sided, some fiber-reinforced. Perforated sheet lets water vapor through; solid sheet is a vapor retarder. At the rafters, the Building America Solution Center found no significant difference between one foil face and two: the first layer already cuts radiant heat gain by at least 90 percent.
- Radiant barrier roof sheathing: OSB or plywood with foil laminated to one side, installed foil side down when a roof deck is replaced.
- Foil bubble insulation: polyethylene bubble wrap faced with foil, sold under product names such as Reflective Air and double bubble. It is reflective insulation, covered below.
- Foil-faced batts: pressed against drywall, the foil faces no air space, so Building Science Corporation calls it a vapor barrier, not a radiant barrier.
- Low-e paint, sold as radiant barrier paint, is properly an interior radiation control coating. The Solution Center puts its emittance under 0.25, short of the 0.1 that defines a radiant barrier.
How a radiant barrier works, and why foil has no R-value
On a sunny day the roof deck gets hot and radiates heat to everything cooler below it: the insulation, the attic floor and any ducts. Fiberglass, cellulose and foam mainly slow heat conducted through them. Foil works on the radiation. The Florida Solar Energy Center explains that aluminum reflects thermal radiation well and emits very little, so foil facing down under a hot roof doesn’t pass the roof’s heat along. Clean foil has an emissivity of about 0.03 to 0.05, a reflectivity of 95 to 97 percent, according to the Department of Energy’s radiant barrier fact sheet from Oak Ridge National Laboratory.
- It needs an air space. The Department of Energy says the reflective surface must face one. Foil rolled out on the deck under new shingles has none, so heat simply conducts through it, the Florida Solar Energy Center notes.
- It needs to stay clean. Dust raises the foil’s emissivity and lowers its reflectivity, the Oak Ridge fact sheet explains.
An R-value rates resistance to conducted heat, and foil in a ventilated attic sits in moving air. When the EPA dropped radiant barriers from its ENERGY STAR insulation program in 2012, it said they have no R-value for that reason and ended ENERGY STAR labeling of them. Building Science Corporation is blunter: radiant barriers do not have R-values, and there is no such thing as R-11 radiant barrier paint.
Reflective insulation is a different product
Foil bubble wrap and multi-layer foil become reflective insulation when the foil faces sealed-in air spaces. That assembly can carry an R-value, but it belongs to the assembly, not the roll. Federal labeling rules require the package to state the number of sheets, the number and thickness of the air spaces, and the R-value for heat flowing up, down and sideways (16 CFR 460.12). The 2024 IECC counts an air space only when it is enclosed on all sides, and has the installer’s certificate list the sheets, air spaces and assembly R-value (Sections R303.1.1 and R303.1.6).
The manufacturers’ association gives assembly values from R-3 to R-21, depending on the application. Take away the air spaces and the number collapses: Building Science Corporation cites Canadian hot box testing of foil bubble insulation with no air space in front of the foil at R-1.5.
Do radiant barriers work in the Northeast?
They reduce summer heat gain everywhere. Whether that saves real money depends on climate, attic insulation and ducts.
- The Department of Energy: more effective in hot climates than cool ones, especially with cooling ducts in the attic. Some studies show a 5 to 10 percent cut in cooling costs in a warm, sunny climate; in cool climates, more insulation is usually the better buy.
- Building America: 8 to 12 percent of cooling costs in hot climates, but seldom cost-effective in cold climates, where thick attic insulation already minimizes heat transfer.
- Insulation level: a radiant barrier cuts the heat flowing into the house from the attic by about 40 percent, the Solution Center says, but at R-30 or better there is very little heat flow left to cut. New Jersey (2024 IECC) and New York (2025 energy code) require R-49 in new attics, Connecticut (2021 IECC) R-60.
- More insulation did more: in tests summarized in the Oak Ridge fact sheet, a radiant barrier over R-19 cut summer ceiling heat gain by 16 to 42 percent, about 2 to 10 percent of the cooling part of the summer bill. Taking the same R-19 attic to R-30 instead cut ceiling heat flow by 27 to 33 percent.
- Winter is weaker: the fact sheet reports smaller reductions in winter, and very little testing in climates colder than Knoxville, Tennessee. The Florida Solar Energy Center adds that the more of your bill goes to heating, the less sense a radiant barrier makes, because while the heat is on, warmth from the attic helps.
What that means in New Jersey, New York and Connecticut
Bills here are weighted toward heat. In the Energy Information Administration’s 2020 household survey, space heating took 28 percent of household energy spending in New Jersey and air conditioning 13 percent; in New York, 32 and 10 percent; in Connecticut, 34 and 9 percent. Florida, where much of the radiant barrier testing was done, is the mirror image: 8 percent heating, 28 percent air conditioning.
In dollars: the average New Jersey household that used air conditioning spent $282 on it in 2020. Apply the Department of Energy’s warm-climate 5 to 10 percent, more than a well-insulated Northeast attic should expect, and that is roughly $14 to $28 a year at 2020 prices. Ducts matter too, but half of Northeast households cool mainly with window and wall units, mini-splits or portables, the EIA reports, and a window unit gains nothing from a cooler attic.
A radiant barrier can still make sense here when the roof deck is being replaced anyway, so foil-faced sheathing adds little cost, or when central air ducts sit in a vented attic under a sunny roof and moving them inside isn’t planned. If the attic is already at R-30 or better, expect little.
Where attic foil goes: under the roof, not on the insulation
The Oak Ridge fact sheet describes the choices: foil fastened to the underside of the roof deck, draped over the rafters before the deck goes on, stapled to the rafters or truss chords, or laid over the insulation on the attic floor. The Solution Center recommends only the roof positions for sheet foil.
Stapled to the rafters or built into the roof deck
- Foil side down. A one-sided barrier works either way at first, but a face pointing up collects dust and loses its effect, the Florida Solar Energy Center says.
- Leave a gap under the deck: the Department of Energy says to let the material droop to make at least a 1-inch air space.
- Keep the vents working. Stop the foil 2 to 3 inches above the attic floor insulation, leave a strip open at the ridge, and cover no vents.
- Keep clear of heat: Building America calls for 3 inches from a chimney, furnace or flue pipe, and foil on the gable ends as well as the roof.
- At a reroof with new decking, foil-faced OSB installed foil side down does the same job with no attic work.
Laid over the attic floor insulation
The Department of Energy strongly recommends against this one:
- Dust. The Oak Ridge fact sheet estimates a dusty attic floor installation loses about half its effectiveness after one to ten years.
- Moisture. In cold weather, water vapor rising from the house can condense, even freeze, under foil lying on the insulation, the fact sheet warns, wetting the insulation, staining ceilings and, in severe cases, rotting framing. Building America says moisture gets trapped under the barrier, with a risk of mold and wood rot.
- Solid foil is a vapor retarder on the cold side of the insulation. The manufacturers’ association accepts attic floor installations only at 5 perms or more, laid loose, over an attic with no moisture problem.
If foil goes on an attic floor at all, it has to be perforated or otherwise vapor permeable, kept off recessed lights and vents. The better choice is not to put it there.
Fire ratings, wiring and shingles
- Fire rating. The Oak Ridge fact sheet says that to meet code a radiant barrier needs an ASTM E84 flame spread index of 25 or less and a smoke-developed index of 450 or less, the limits the International Residential Code sets for insulation and facings in attics (Section R302.10.1 of the 2021 edition Connecticut uses and the 2024 edition New Jersey and New York adopted).
- Product standards. The 2024 IECC in New Jersey and New York requires any radiant barrier installed to meet ASTM C1313 and be installed to ASTM C1743 (Section R303.2.2); Connecticut’s 2021 edition has no such section. Building America notes that a radiant barrier doesn’t reduce the attic insulation the code requires.
- Not an ignition barrier. Foil isn’t on the code’s list of ignition barriers for attic spray foam, which includes 1 1/2 inches of mineral fiber or cellulose and 3/8-inch gypsum board (R303.5.3 of the 2024 IRC, R316.5.3 in 2021). The manufacturers’ association adds that foam sprayed against a radiant barrier cancels its benefit.
- Wiring. Foil conducts electricity. The Department of Energy warns against contact with bare wiring, and the Florida Solar Energy Center says never staple through or over it.
- Shingles. The Florida Solar Energy Center measured peak shingle temperatures only 2 to 5 degrees F higher over an attic radiant barrier; the Oak Ridge fact sheet cites 2 to 10 degrees for roof-mounted barriers, with any effect on roof life unknown.
What to do first in a Northeast attic
- Seal the attic floor: top plates, chases, recessed lights, flues and the hatch. ENERGY STAR says sealing leaks and adding insulation can save up to 10 percent on annual energy bills. See air sealing.
- Bring the insulation up to ENERGY STAR levels. In every climate zone in our service area, ENERGY STAR recommends R-60 for an uninsulated attic, or R-49 added over 3 to 4 inches already there. See attic insulation and recommended R-values.
- Deal with attic ducts. Building America notes that ducts in a vented attic can raise energy bills, and lists the fixes: seal and insulate them, convert to an unvented attic, or go ductless when the system is replaced. The energy code requires R-8 on ducts 3 inches and larger outside conditioned space (Section R403.3.3 of the 2024 IECC, R403.3.1 in 2021).
- Consider spray foam at the roof deck when the attic holds ducts or an air handler, the roof has hips, valleys or dormers that are hard to ventilate, or the attic is becoming a room. Foam under the deck makes the attic indoor space, and Building America says radiant barriers belong only in vented attics. Foam costs much more than blown insulation; see roof insulation and spray foam insulation.
We air seal, blow in cellulose and fiberglass, install fiberglass and mineral wool batts and rigid foam board, spray open and closed cell foam, and install radiant barrier at the rafters where it fits. If you want foil-faced sheathing, the time is a reroof, and the roofer installs it foil side down. How the materials compare: types of insulation.
Foil bubble insulation on basement walls, ducts, garage doors and pipes
Wherever foil bubble insulation goes, its label R-value depends on air spaces, and the foil is a vapor barrier.
- Basement walls. Building America says an insulated basement wall must dry to the inside, with no foil, plastic or vinyl wallpaper on the room side; foil-faced polyiso board may be the exception. Building Science Corporation describes foil over furring on the inside of Florida block walls that became a vapor barrier on the wrong side, with mold behind it. Code asks for R-10 continuous or R-13 in New Jersey’s zone 4 counties, and R-15 continuous, R-19, or R-13 plus R-5 in its zone 5 counties (2024 IECC), Connecticut (2021 IECC) and New York (2025 code). We use closed cell spray foam or rigid board; see basement insulation.
- Ducts. Code calls for R-8 on most ducts outside conditioned space, and Building Science Corporation says a quarter inch of bubble wrap on a duct is not R-4. Duct wrap packages must show R-value and thickness under federal rules, so read the label. Building America says ductwork should be sealed with mastic, not ordinary duct tape.
- Garage doors. A foil bubble kit’s R-value applies only to the air spaces and heat flow direction its label states, so compare those with how the kit is installed. A door kit makes the garage milder but rarely fixes a cold room above; see garage insulation.
- Pipes. The energy code sets R-3 as the minimum for heating and cooling system piping (Section R403.4, 2021 and 2024 IECC). Whatever the wrap, look for a stated R-value that meets it.
What radiant barriers cost, and installing one yourself
The reflective insulation manufacturers’ association puts installation of standard radiant barrier sheathing on a new house needing 1,500 square feet at $300 to $500 on average, $600 to $2,000 for larger or more complex jobs, and a 500-square-foot roll for do-it-yourselfers at 14 to 20 cents a square foot. When foil comes bundled in an energy package, the Florida Solar Energy Center advises asking for an itemized price, and says higher prices appear to reflect marketing more than performance.
Most of our projects, which are air sealing and insulation, run between $3,500 and $12,500. State and utility programs offer rebates for that work; see New York and New Jersey insulation rebates and Connecticut insulation rebates. The federal 25C tax credit ended for anything placed in service after 31 December 2025.
Can you install a radiant barrier yourself?
Yes. The Florida Solar Energy Center and the Building America Solution Center both publish step-by-step retrofit instructions. Their safety points: work with a partner, early in the day or in cool weather, because attic daytime temperatures can climb far above 100 degrees F; step only on the framing or a board across it, never on insulation or drywall; wear a hard hat against roofing nails, plus goggles, long sleeves and a mask; and never staple near wiring. Don’t crush the insulation already there: the Oak Ridge fact sheet notes an R-19 batt squashed to 3 1/2 inches is roughly R-13.
Common questions about radiant barriers and attic foil
Do radiant barriers work in cold climates?
They cut summer heat gain anywhere, but pay back poorly where heating dominates. The Department of Energy says adding insulation is usually more cost-effective in cool climates, Building America calls radiant barriers seldom cost-effective in cold climates, and tests summarized by Oak Ridge National Laboratory found smaller reductions in winter than in summer.
Is a radiant barrier worth it in New Jersey, New York or Connecticut?
Rarely as a purchase on its own. Heating takes a much bigger share of household energy spending than air conditioning in all three states, and research finds little benefit once an attic reaches R-30. It can make sense as foil-faced sheathing during a reroof, or over attic ducts under a sunny roof. Seal and insulate first.
Does attic foil have an R-value?
No. A radiant barrier reflects radiant heat and has no R-value of its own; the EPA dropped radiant barriers from ENERGY STAR insulation labeling in 2012 for that reason. Reflective insulation, such as foil bubble wrap facing an enclosed air space, can have an assembly R-value, which depends on the air spaces its label describes.
Can I lay radiant barrier foil on top of my attic insulation?
The Department of Energy strongly recommends against it. Foil facing up collects dust, and Oak Ridge estimates a dusty attic floor installation loses about half its effectiveness in one to ten years. In cold weather, vapor from the house can condense underneath. Staple it to the rafters, foil side down, instead.
Can a radiant barrier cause mold?
It can, in the wrong place. Building America warns that a barrier in contact with attic floor insulation traps moisture, with a risk of mold and wood rot, and Building Science Corporation documents mold behind foil on the inside of masonry walls. Under the roof, Building America recommends a perforated product with gaps for air flow above, below and behind it.
Should I use perforated or solid radiant barrier?
Perforated for attic work. Building America recommends it because it is less likely to trap vapor, and any foil laid on an attic floor must let vapor through. Solid foil is a vapor retarder. Very large holes raise the foil’s emissivity and lower its performance, the Oak Ridge fact sheet notes.
Will a radiant barrier damage my shingles?
It’s unlikely. The Florida Solar Energy Center measured peak shingle temperatures only 2 to 5 degrees F higher over an attic radiant barrier, and the Oak Ridge fact sheet cites 2 to 10 degrees for roof-mounted barriers and says any effect on roof life is unknown. Ask the shingle manufacturer to confirm the warranty in writing.
Is a radiant barrier or spray foam better?
They do different jobs. Spray foam under the roof deck insulates, air seals and turns the attic into indoor space, which suits attics with ducts or an air handler. A radiant barrier only reflects heat, belongs in a vented attic, and loses its benefit if foam is sprayed against it. Foam costs far more; in a plain vented attic, air sealing and blown insulation come first.
How much does a radiant barrier cost?
The reflective insulation manufacturers’ association puts installation of radiant barrier sheathing on a 1,500-square-foot new house at $300 to $500 on average, up to $2,000 for larger or complex jobs, and rolls for do-it-yourselfers at 14 to 20 cents a square foot. Most of our projects run between $3,500 and $12,500.
What should come before attic foil?
Air sealing and insulation to ENERGY STAR depth. We air seal and install spray foam, blown-in cellulose and fiberglass, batts and rigid foam board, and we install radiant barrier where it fits. A free energy audit shows whether foil would add anything in your attic. For foil-faced roof sheathing, decide before a reroof.
Free energy audit
Before you buy foil, we look at the attic you have: insulation depth, air leaks, ventilation, ducts and any sign of moisture. If a hot upstairs is the complaint, we explain what is driving it and what will fix it, in a written scope at no charge. See what an energy audit covers.
Call 914-554-2289 or use the contact form, 8am–8pm, seven days. The Home Insulators is family-owned, based in New Rochelle, NY since 2015, with a 100-plus-person in-house crew that never subcontracts. We work across all of New Jersey, all of Connecticut, New York’s Hudson Valley and Long Island; see our service area.