A dark asphalt roof on a summer afternoon reaches about 170 degrees Fahrenheit. A white membrane on the same building on the same day sits near 105. That is a 65 degree difference produced by nothing but color, and it is not controversial: you can calculate it from first principles, and this article will, because the arithmetic is the part that makes the rest of the story make sense.
What is contested is not the physics. It is whether anyone should be allowed to require it. Over the last decade, trade associations representing manufacturers of dark roofing have run a quiet and largely successful campaign against cool roof provisions in building codes, city by city and standard by standard. That campaign is documented in public records and investigative reporting, and most homeowners have never heard of it.
This article covers three things: the real physics of how hot a roof gets and why reflectance alone does not answer it, the arithmetic of what a cool roof is worth in your specific building, and the two things that outperform a cool roof if what you want is a cooler house and a smaller bill.
What actually determines how hot a roof gets
Almost everyone believes roof temperature is about color. Color is half of it. The other half gets left out of nearly every article on the subject, and leaving it out is how people end up buying a roof that runs hot while believing it is cool.
Two independent surface properties control the outcome:
Solar reflectance (also called albedo) is the fraction of incoming sunlight the surface bounces straight back, on a scale of 0 to 1. Dark asphalt is around 0.08, meaning it absorbs 92 percent of the sun that hits it. A new white membrane is around 0.80.
Thermal emittance is the surface’s ability to radiate heat away as infrared once it has absorbed it, also 0 to 1. Most non-metallic building materials, including asphalt, paint, and membranes, are around 0.85 to 0.90. Bare metal is dramatically lower, often 0.05 to 0.15.
Reflectance decides how much heat gets in. Emittance decides how easily it gets back out. A surface needs both to stay cool, and the combined figure is standardized as the Solar Reflectance Index (SRI) under ASTM E1980, scaled so that a standard black surface is 0 and a standard white one is 100.
The numbers, for the roofs you can actually buy
| Roof surface | Solar reflectance | Thermal emittance | Peak surface temp | SRI |
|---|---|---|---|---|
| Dark asphalt shingle | 0.08 | 0.90 | 170°F | 4 |
| Weathered mid-grey shingle | 0.20 | 0.90 | 160°F | 19 |
| Bare Galvalume or galvanised metal | 0.60 | 0.10 | 149°F | 34 |
| Aged white membrane | 0.65 | 0.90 | 118°F | 79 |
| Cool-coated white metal | 0.70 | 0.85 | 115°F | 85 |
| New white membrane | 0.80 | 0.90 | 104°F | 100 |
Three things fall out of that table.
Bare metal is not a cool roof. This is the most commercially useful thing in this article, because a great many people buy a metal roof believing they have solved the heat problem. Unpainted metal reflects well and radiates terribly, so it absorbs less and then holds what it absorbs. It lands closer to asphalt than to white. A coated metal roof with a high-emittance finish is a genuinely excellent cool roof, at SRI 85. The difference between those two metal roofs is the coating, not the metal, and it is worth asking about by name.
Aging matters more than the brochure admits. A white membrane at 0.80 reflectance drifts toward 0.65 as it collects dirt, algae and pollution, typically within the first three years. That is why standards increasingly specify a three-year aged value, and why the number to plan against is the aged one, not the figure on the brochure.
Nothing beats white, but you do not have to accept white. “Cool colored” pigments reflect strongly in the near-infrared, where more than half of the sun’s energy sits, while looking like an ordinary dark color to the eye. A cool-pigmented brown shingle will not match a white membrane, but it can double the reflectance of a conventional one of the same shade. This technology came largely out of Lawrence Berkeley National Laboratory’s Heat Island Group and it is available now.
What that is worth in your house, in dollars
Here is where most cool roof advocacy overreaches, so we will do the arithmetic rather than quote a brochure. Heat entering through your ceiling is Q = U × A × ΔT, where U is the inverse of your insulation’s R-value, A is area, and ΔT is the temperature difference between attic and living space. Take 2,000 square feet, an indoor temperature of 75, and an attic that runs 130 under a dark roof or 105 under a cool one.
| Ceiling insulation | Dark roof, attic 130°F | Cool roof, attic 105°F | Heat avoided | Cooling cost saved |
|---|---|---|---|---|
| R-13 | 8,462 BTU/hr | 4,615 BTU/hr | 3,846 BTU/hr | about $56/yr |
| R-19 | 5,789 BTU/hr | 3,158 BTU/hr | 2,632 BTU/hr | about $38/yr |
| R-30 | 3,667 BTU/hr | 2,000 BTU/hr | 1,667 BTU/hr | about $24/yr |
| R-49 | 2,245 BTU/hr | 1,224 BTU/hr | 1,020 BTU/hr | about $15/yr |
Cost figures assume 1,200 cooling hours, a SEER 14 system and 17 cents per kilowatt hour.
If those numbers look underwhelming, that is because they are, and you should distrust anyone who tells you otherwise. On a well-insulated house with no ductwork in the attic, a cool roof is a modest energy measure. Insulation is a better first purchase, and if you are choosing between them, insulate.
But the picture changes completely in four situations, and most buildings are in at least one of them.
Your ducts are in the attic. This is the big one, and it applies to a large share of American housing. Run the same calculation for 150 feet of R-6 flex duct carrying 55 degree supply air, and a dark roof adds about 4,900 BTU/hr of parasitic gain against 3,300 for a cool roof. That 1,600 BTU/hr roughly doubles the benefit calculated above, and it is exactly why the Department of Energy notes that these measures work best when cooling ducts are in the attic. You are paying to cool air that a 130 degree attic is reheating on its way to your rooms.
Your building is not air conditioned at all. A shop, barn, garage, greenhouse or workshop has no thermostat to hide the problem. Here the roof is not saving you money, it is the entire difference between a space you can work in during August and one you cannot. The dollar figure is zero and the value is high.
Peak demand and equipment size. A cool roof cuts the worst hour of the worst day, which is the hour that determines what size air conditioner you need. Reducing peak load can let you install smaller equipment, and that capital saving usually dwarfs the annual energy saving.
The roof itself lasts longer. Asphalt spends its life at 170 degrees, cycling. Heat drives the volatile loss and embrittlement that ends a shingle’s life. A cooler roof ages more slowly, which is a real economic benefit that never shows up on an energy bill.
Why this is fought at the code level rather than the showroom
Hold those modest per-house numbers in mind, because they explain the politics. If a cool roof saved a homeowner four hundred dollars a year, the market would sort it out and no ordinance would be necessary. It saves a few tens of dollars, so individuals reasonably choose on looks and price.
The collective effect is a different quantity entirely. Roofs are roughly 20 to 25 percent of an urban surface. Change their albedo across a city and you measurably lower ambient air temperature, which lowers everyone’s cooling load including buildings that did nothing, reduces peak grid strain on the days grids fail, and cuts heat deaths, which are the deadliest weather hazard in the United States. That is a public good that no individual purchase decision captures, which is the textbook definition of something that ends up in a building code.
Which is precisely why the fight happens in code hearings, where almost nobody is watching.
The dark roof lobby, and what the record shows
We want to be careful here, because this subject attracts more heat than evidence. What follows is the documented record, with sources at the end. Where we could not document something, we say so.
The organized opposition to cool roof requirements is real, it is well funded, and it has been winning. The lead actor in the public record is not the asphalt industry but the EPDM Roofing Association, the trade group for black rubber membrane, whose executive director Ellen Thorp also runs a group called the Coalition for Sustainable Roofing. The Asphalt Roofing Manufacturers Association has worked alongside it. The documented campaign includes:
Denver, 2015. A letter-writing campaign by EPDM advocates defeated a proposed cool roof requirement. A far narrower ordinance, applying only to new commercial buildings over 25,000 square feet, passed three years later in 2018.
ASHRAE, ongoing. The industry opposed a proposed change to ASHRAE standards that would have extended reflective roof requirements into climate zones 4 and 5, the temperate middle of the country. ASHRAE rejected the change. Thorp has described the result plainly: they have been able to stop those requirements from reaching zones 4 and 5.
Baltimore, 2022. Both associations lobbied against the city’s cool roof ordinance, arguing that dark roofs are more efficient in northern climates and that current research did not support cool roofs for energy efficiency or heat island reduction. The ordinance passed anyway in 2023.
Tennessee, 2025. Thorp’s coalition worked with a lobbyist on legislation eliminating the state’s cool roof requirement. Lawmakers passed it. A rule that had applied to 14 counties was repealed and a planned expansion to 20 more was reversed.
ARMA’s public position is not “cool roofs are bad.” It is subtler and more effective than that: the association argues for a whole building approach, in which roof reflectance is merely one factor among insulation, shading and climate, and should not be singled out by prescriptive requirement. Its executive vice president Reed Hitchcock has framed this as preserving design flexibility and consumer choice.
That argument is not stupid, and it deserves a straight answer rather than a sneer. A whole building approach genuinely is better engineering than any single prescriptive rule. It is also, conveniently, unenforceable in a way that a reflectance number is not. A code official can measure SRI. Nobody can inspect a philosophy. When an industry proposes replacing a measurable requirement with a holistic one, the practical effect is usually that the requirement disappears, and that is what happened in Tennessee.
As for motive, one specific and sourced observation is worth more than speculation. Industry consultant Brian Whelan has noted that manufacturers likely earn higher margins on EPDM systems than on white TPO alternatives, because the black rubber systems require high-margin accessories such as seam tapes and sealants that the alternative does not. The incentive is in the accessories, not in some grand plan about your thermostat.
What we could not document: an HVAC industry campaign. It is a reasonable suspicion, since equipment manufacturers plainly benefit when buildings need larger air conditioners, and reduced peak load is explicitly one of the things a cool roof delivers. But we found no evidence of HVAC trade groups lobbying against cool roof provisions, and we are not going to assert one because it would be satisfying. The structural incentive exists. The campaign, on the record, belongs to the roofing membrane manufacturers.
The heating penalty argument, taken seriously
The industry’s technical case rests on one real effect, and it deserves a fair hearing rather than dismissal. A reflective roof that rejects sunlight in July also rejects it in January, when you would have liked the free heat. That is the heating penalty, and it is genuine.
It is also much smaller than the cooling benefit in most of the country, for three reasons that rarely get stated together. Winter days are short and the sun is low, so far less energy strikes the roof in the first place. Winter skies are cloudier across most of the US. And snow cover, when present, makes every roof white regardless of what you paid for.
Weighed fairly, cool roofs are a clear net win in climate zones 1 through 3, a close call in zones 4 and 5 depending on the specific building, and a probable net loss in zones 6 through 8. Which means the industry is not wrong that a one-size-fits-all national mandate would be poor policy. They are simply applying a valid argument about Minnesota to defeat requirements in Tennessee, which is a different thing, and it is the part worth noticing.
If you are in a cold climate, this article’s recommendation is not a white roof. It is the radiant barrier and the solar array below, both of which work in your favor year-round.
Radiant barriers: the air gap is the whole product
A radiant barrier is a sheet of low-emittance foil installed in the attic, and it addresses a different transfer path than insulation does. Your hot roof deck radiates infrared downward at the top of your insulation. Fiberglass does not stop radiation particularly well; it slows conduction. Foil stops radiation almost completely.
The physics is a two-surface radiation exchange, and the effective emittance between two parallel surfaces is:
εeff = 1 ÷ (1/ε1 + 1/ε2 − 1)
A bare wood deck at emittance 0.90 facing insulation at 0.90 gives an effective emittance of 0.818. Introduce foil at 0.05 and it becomes 0.0497. That is a 94 percent reduction in radiant transfer across the attic, from a material that costs a few hundred dollars.
How to install one
Position it under the rafters, foil facing down into the attic. Staple the foil to the underside of the roof rafters, leaving the existing ventilation channel above it clear. This keeps the reflective face pointed at an open air space, keeps dust off it, and avoids trapping moisture in the insulation.
Maintain at least three quarters of an inch of air space on the reflective side. This is the requirement the entire product depends on.
Do not block soffit vents or the ridge. Attic ventilation still has to work. Stop the foil short at both ends.
Do not lay it flat on top of your insulation unless you have no alternative. Face-up foil collects dust, which raises its emittance and degrades performance, and it can trap moisture in the insulation below. The good news on dust, from Florida Solar Energy Center research, is that degradation is real but not fatal: even at an emittance degraded to 0.20 you retain roughly three quarters of the benefit.
Perforated products exist for a reason. If there is any chance of vapor drive into the attic, use perforated foil so the assembly can dry.
Expect 5 to 10 percent off cooling costs, not a miracle. That is the Department of Energy’s figure for warm sunny climates, and it is larger when the ducts are in the attic. In cool climates, DOE is explicit that adding insulation is more cost-effective than adding a radiant barrier, and we agree.
Solar panels: the best thing you can put on a roof
Now the part that makes the entire cool roof debate look small.
A photovoltaic array shades your roof. That is not a side effect, it is measurable, and it was quantified in the first peer-reviewed study of the phenomenon, by Anthony Dominguez and Jan Kleissl at UC San Diego, published in Solar Energy in 2011. Using thermal imaging on a campus building they found the ceiling under panels was 5 degrees Fahrenheit cooler than under exposed roof, and that the panels cut heat reaching the roof by about 38 percent. The benefit was larger where an open air gap let air circulate beneath the panels, so tilted racking outperformed flush mounting. At night the effect reverses helpfully: panels reduce radiant loss to the sky, trimming winter heating.
One clarification on mechanism, because the popular description gets it backwards. Panels do not “pull heat out of” your roof. They intercept sunlight before it reaches the roof, convert about 20 percent of it into electricity, and dump most of the rest into air moving through the gap underneath. The roof stays cooler because it is in shade, and the gap is what keeps the shade from simply becoming a hot lid. That is why racking height and tilt matter, and why an installer who mounts panels tight to the deck has thrown away the thermal benefit.
Then there is the part that is not close:
| Measure on a 2,000 sq ft R-30 house | Annual value |
|---|---|
| Cool roof instead of dark asphalt | about $24 |
| Radiant barrier, warm climate | 5 to 10% of cooling |
| 6 kW rooftop solar array | about $1,340 |
Roughly fifty times the cool roof, from the same square footage, while also shading it. Figures assume 4.5 peak sun hours, an 80 percent system derate and 17 cents per kilowatt hour; your numbers move with local sun, rates and net metering rules, and net metering is the variable that has changed most in recent years and deserves checking before you sign anything.
Three caveats belong with that number. It is a capital project measured in five figures rather than a weekend. It needs a roof with enough remaining life that you are not paying to strip and reinstall the array in six years. And shading from trees kills output far faster than most homeowners expect. If you are considering it as part of a broader resilience plan rather than purely as an investment, our guides to solar power kits for off-grid living and sizing backup power that actually works cover the difference between a grid-tied array that shuts down in an outage and a system that keeps your refrigerator running. That distinction catches a lot of people by surprise at the worst possible moment.
Where to spend your money, by situation
Hot climate, replacing a roof soon: specify by SRI, not by color. Ask for the three-year aged value. Cool-pigmented shingles let you keep a dark appearance and still roughly double reflectance.
Hot climate, roof not due for replacement: skip the roof, do the radiant barrier. A few hundred dollars, a weekend, and it works on the roof you already have.
Ducts in the attic, any climate: this is your highest-value target. Cool roof, radiant barrier, and sealing and insulating the ducts themselves. You are currently air conditioning an attic.
Cold climate: do not chase a white roof. The heating penalty is real where you live. Insulate, add a radiant barrier if the attic runs hot in summer, and consider solar, which pays in every season.
Unconditioned shop, barn or garage: the cheapest transformation available to you is a reflective roof coating plus a radiant barrier. There is no air conditioner masking the problem, so the roof is the whole story. This is also the building where a mistake is cheap, which makes it the right place to learn.
Considering metal: ask specifically about the coating’s emittance, not just its color or reflectance. Bare Galvalume is not a cool roof. Coated metal at SRI 85 is an excellent one.
Anyone: look up your jurisdiction before you assume what is allowed or required, since as this article describes, the rules in your state may have changed recently and not in your favor. Our guide to local laws and regulations covers the general habit.
The broader point is the one worth carrying away. A roof is the largest solar collector you own, and you own it whether or not you use it. Right now most American roofs absorb about 90 percent of everything the sun delivers and convert it into a cooling bill. The physics of doing better has been settled for forty years. What has not been settled is who gets to require it, and that argument has been running in rooms you were not invited to.
References
The lobbying record. Floodlight News, “This little-known ‘dark roof’ lobby may be making your city hotter” (2025), the primary investigative account, syndicated by WWNO and others. Engineering News-Record, “The Little-known ‘Dark Roof’ Lobby May Be Making Cities Hotter”. Roofing Contractor, “The Battle Over Cool Roofs Heats Up Following Tennessee Rollbacks”, trade-press coverage from inside the industry.
The industry’s own position, in its own words, which we recommend reading rather than taking our summary for: ARMA’s Steep-Slope Cool Roofing white paper (2020), and the EPDM Roofing Association’s “Cool Roofs in Northern Climates”, which is the heating-penalty argument in full.
The science. Lawrence Berkeley National Laboratory’s Heat Island Group on cool roofs, the group that did much of the foundational work including cool-colored pigments. LBNL’s Status of Cool Roof Standards in the United States. The Cool Roof Rating Council, which maintains the third-party rated product directory where you can look up any specific roofing product’s reflectance and emittance.
Radiant barriers. US Department of Energy, Radiant Barriers, the plain-language official guidance including the 5 to 10 percent figure, the requirement that the reflective surface face an air space, and the advice that insulation beats a radiant barrier in cool climates. (Linked to an archived copy: the Energy Saver page was reorganised off this address and the live URL now returns an error.) Florida Solar Energy Center, “Radiant Barriers: A Question and Answer Primer”, the most useful practical document on installation and on the dust question. Installation practice is also covered by ASTM C1158.
Solar panels as shade. A. Dominguez, J. Kleissl and J. C. Luvall, “Effects of Solar Photovoltaic Panels on Roof Heat Transfer”, Solar Energy, 2011, the peer-reviewed source of the 38 percent and 5 degree figures. UC San Diego’s plain-language summary of the same work.
Standards referenced: ASTM E1980 (Solar Reflectance Index), ASTM C1549 and C1371 (measuring reflectance and emittance), ASTM C1158 (radiant barrier installation).
