A metal roof with a reflective finish bounces more of the sun’s energy back into the sky than a dark asphalt roof, which keeps your attic cooler and gives your air conditioner less to do. How much you save on energy depends on your climate, your attic insulation and ventilation, and the color and finish you pick. This guide explains what a cool roof is, how metal roof energy savings happen, and how to get the real benefit instead of the sales pitch.
What makes a roof cool
Two measured properties decide how hot a roof surface gets in the sun. The first is solar reflectance, the share of sunlight the surface bounces away. The second is thermal emittance, how readily the surface releases the heat it has absorbed back to the sky. A surface that scores high on both stays coolest. Painted metal scores high on emittance regardless of color, and its reflectance depends on the color and the pigments in the paint.
Reflectance and emittance
Think of reflectance as how much heat never gets in, and emittance as how fast the roof gets rid of the heat that did. A white painted metal roof has high reflectance and high emittance. A dark shingle roof has low reflectance and decent emittance, so it soaks up heat all day. Bare metal such as unpainted Galvalume reflects well but has low emittance, so it holds heat once it warms up. Both numbers are combined into a single Solar Reflectance Index in some codes and product listings.
Infrared-reflective pigments
Roughly half of the sun’s energy arrives as near-infrared light you cannot see. Cool pigments are designed to reflect that invisible part while still looking like a normal color to your eye. That is how a dark bronze or charcoal metal roof can stay noticeably cooler than the same color in an ordinary paint. Most PVDF paint lines from major coil coaters now include infrared-reflective pigments in their standard colors, and many SMP lines do too. Our guide to PVDF versus SMP finishes explains the paint systems themselves.
Light colors versus dark colors
| Roof surface | Solar reflectance | Thermal emittance | Summer attic effect |
|---|---|---|---|
| White or very light painted metal | High | High | Coolest option |
| Light gray, tan or light stone painted metal | Medium-high | High | Cool |
| Medium colors with infrared-reflective pigments | Medium | High | Noticeably cooler than standard |
| Dark colors with infrared-reflective pigments | Low-medium | High | Cooler than you would expect from the color |
| Bare Galvalume | High when new, lower as it weathers | Low | Reflects well but holds heat |
| Dark asphalt shingles | Low | Medium-high | Hottest common roof |
These are relative tiers, not test results. The rated numbers for a specific color and finish are published by the Cool Roof Rating Council, and your installer or the panel manufacturer can give you the values for the exact product in your bid. Our metal roof colors guide covers how to weigh heat against looks.
Where the heat goes
On a summer afternoon a dark roof surface can be far hotter than the air around it. That heat radiates down into the attic, warms the insulation and the ductwork running through it, and eventually pushes into the rooms below. Lowering the surface temperature with a reflective roof is the first step. The next steps are stopping the heat that still gets through and letting the attic breathe.
Above-sheathing ventilation
Metal roofs can be installed on battens or over a vented spacer rather than flat on the deck. That creates an air channel between the panel and the sheathing, open at the eave and vented at the ridge, and warm air rising through it carries heat away before it ever reaches the deck. Installers call this above-sheathing ventilation. It works with standing seam, metal shingles and stone-coated steel, and in cold climates it also helps keep the roof deck cold, which reduces ice dams. It adds material and labor, and it changes the wind and fire listings for the assembly, so ask about it rather than assuming.
Insulation and air sealing still come first
A cool roof lowers the attic temperature. Insulation and air sealing decide how much of whatever heat remains reaches your living space. If your attic is under-insulated or has gaps around ducts, can lights and the attic hatch, fixing those will usually do more for your bills than any roof color, and a reroof is a good time to do it because the ceiling is not disturbed. Soffit intake and ridge exhaust vents keep the attic air moving. Our underlayment and ventilation guide goes into what belongs under the metal.
Which climates benefit most
The payoff is largest where the cooling season is long and the sun is strong: the Sun Belt, the Southwest, Texas, Florida and the Gulf Coast. Homeowners there often notice the difference in the attic on the first hot day. Mixed climates in the middle of the country see a moderate benefit in summer with little effect in winter. In cold northern climates the cooling savings are small, and a reflective roof gives up a little winter solar gain, though the loss is minor because winter sun is weak and the roof is often under snow. There, choose color for looks and durability and treat energy as a bonus.
Metal has one more advantage in any climate: it has very little thermal mass. Once the sun goes down a metal roof cools within minutes, while a heavy tile or asphalt roof keeps radiating stored heat into the attic well into the evening.
Codes, ratings and incentives
Some energy codes require cool roofs on certain projects in hot climate zones; California’s Title 24 is the best-known example, and it uses rated reflectance and emittance values to define what qualifies. Local utilities sometimes offer rebates for cool roofing, and federal tax rules on roofing have changed several times over the years. Check what applies today with your utility and a tax professional rather than taking a roofer’s word for it, and get the product’s rating sheet so you can prove what you installed.
Cool roofs by metal roof style
- Standing seam and metal shingles in painted steel or aluminum: the full range of rated colors is available, and PVDF finishes hold their reflectance longest.
- Stone-coated steel: reflectance depends on the granule color, and lighter blends stay cooler; the textured surface and the air space under some profiles help too.
- Bare Galvalume: bright and reflective at first, but with low emittance and a surface that dulls over time; fine for barns and modern looks, less reliable as an energy strategy.
- Copper and zinc: these develop natural patinas that are not especially reflective; people choose them for the look and the 100-year life, not for energy.
Finding an installer who thinks about heat
Good metal roofers in hot climates talk about color ratings, ventilation and insulation without being prompted. Our directory lists metal roofing companies by state, and you can filter by style and metal to find installers who work with the finish you want.
Frequently asked questions
Does a metal roof really lower cooling costs?
It can, especially in hot, sunny climates. A reflective metal finish sends more of the sun's energy back to the sky instead of into your attic, and metal sheds the heat it does absorb quickly after sunset. The size of the saving depends on your climate, the color and finish you choose, how well the attic is insulated and vented, and how much you run the air conditioner. Nobody can promise a percentage for your house.
Do dark metal roofs still reflect heat?
Dark colors reflect less visible light than light colors, but many dark metal roof finishes use infrared-reflective pigments that bounce the part of sunlight you cannot see. A dark bronze or charcoal with cool pigments stays cooler than the same color in a standard paint, though still warmer than white or light gray. Ask for the rated reflectance of the exact color rather than guessing from how it looks.
Is a metal roof bad for heating bills in a cold climate?
The effect is small. A reflective roof gives up a little winter solar gain, but winter sun is weak, days are short and the roof is often covered in snow when it would matter most. Attic insulation and air sealing control winter heating costs far more than roof color does. In cold regions most homeowners choose a metal roof color for looks and durability and treat energy as a secondary factor.
What is a cool roof rating?
A cool roof rating reports two measured values for a roofing product: solar reflectance, which is how much sunlight it bounces away, and thermal emittance, which is how readily it releases heat it has absorbed. The Cool Roof Rating Council publishes these values for rated colors and finishes, both new and after three years of weathering. Some building codes use the ratings to define which roofs qualify as cool in hot climate zones.
Is bare Galvalume a cool roof?
Partly. Unpainted Galvalume reflects a lot of sunlight when new, but bare metal has low thermal emittance, which means it holds the heat it does absorb instead of radiating it away. Painted finishes have much higher emittance. Whether bare Galvalume qualifies as a cool roof depends on the rating system in use and how the surface weathers. If energy is a priority, a light painted PVDF finish is the safer bet.