Cool Roofs: How Reflective Coatings Cut Your Energy Bills

On a hot summer afternoon, a dark asphalt roof can reach 150–190°F. A white or light-colored roof under the same sun stays 50–80°F cooler. That temperature difference doesn’t stay on the roof — it flows directly into your attic, your HVAC system, and your utility bill. Cool roofs are one of the most cost-effective tools available for reducing cooling loads in warm climates, and they’ve gotten considerably more accessible over the past decade.

This guide covers the science, the products, the realistic energy savings, and how to apply them.

The Science: How Cool Roofs Work

Two physical properties determine how a roofing surface handles solar energy.

Solar Reflectance (Albedo)

Solar reflectance measures the fraction of solar energy reflected away from the surface, expressed as a decimal from 0 to 1 (or as a percentage). A surface with a reflectance of 0.10 absorbs 90% of solar energy. A surface with a reflectance of 0.80 absorbs only 20%.

Standard dark asphalt shingles have solar reflectance around 0.05–0.15. White elastomeric coatings can achieve 0.80–0.90.

Thermal Emittance

Emittance measures how efficiently a surface releases absorbed heat as infrared radiation, again on a 0–1 scale. A high-emittance surface (0.85+) sheds heat quickly. A low-emittance surface (like polished metal) retains absorbed energy.

Most roofing materials — including asphalt, concrete, and coated surfaces — have naturally high emittance (0.85–0.95). Metal is the exception: bare metal has emittance as low as 0.10, which is why unpainted metal roofs can actually get very hot despite being reflective.

Solar Reflectance Index (SRI)

The Solar Reflectance Index combines both values into a single number that rates a surface’s overall ability to reject solar heat. SRI runs from 0 (a standard black surface) to 100 (a standard white surface). Higher is cooler.

• Standard dark asphalt shingles: SRI ~0–5
• Standard mid-gray membrane: SRI ~20–30
• White TPO or EPDM membrane: SRI ~80–100
• Elastomeric cool roof coating: SRI ~80–110

Some highly reflective surfaces can actually exceed 100 on the SRI scale.

ENERGY STAR Cool Roof Requirements

The ENERGY STAR program certifies cool roofing products that meet minimum reflectance thresholds. Requirements differ by roof slope:

Low-slope roofs (≤ 2:12 pitch):

• Initial solar reflectance: ≥ 0.65
• Reflectance after 3 years of weathering: ≥ 0.50
• Initial thermal emittance: ≥ 0.90

Steep-slope roofs (> 2:12 pitch):

• Initial solar reflectance: ≥ 0.25
• Reflectance after 3 years of weathering: ≥ 0.15
• Initial thermal emittance: ≥ 0.90

The lower threshold for steep-slope products reflects the reality that steep roofs see a lower angle of direct solar radiation, and highly reflective steep-slope products (light-colored metal, white shingles) are less common. Still, even the 0.25 reflectance requirement is substantially better than standard dark asphalt.

The ENERGY STAR-rated product directory is searchable at energystar.gov and lists certified products by manufacturer.

Types of Cool Roof Products

1. Elastomeric Roof Coatings

Elastomeric coatings are thick, acrylic- or silicone-based liquid coatings applied directly to an existing roof surface. They’re the most common cool roof upgrade for both residential and commercial flat roofs.

How they work: Applied at 1.5–2 gallons per 100 sq ft in two coats, elastomeric coatings form a seamless, flexible membrane that reflects solar energy and provides secondary waterproofing. They adhere to asphalt, modified bitumen, metal, and concrete substrates.

Performance: Quality white elastomeric coatings achieve solar reflectance of 0.80–0.90 and SRI values of 100+. They easily meet ENERGY STAR low-slope requirements.

Longevity: A properly applied elastomeric coating over a sound substrate lasts 10–15 years before recoating is needed. Silicone-based formulations generally last longer and tolerate ponding water better than acrylic; acrylic is easier to clean and repaint.

Best applications: Low-slope commercial and residential roofs (flat or up to approximately 2:12 pitch), applied over existing membrane or built-up roofing.

Cost: $0.15–$0.35 per sq ft for DIY material cost; $0.50–$1.50 per sq ft installed professionally.

2. Reflective Roof Paint

Reflective roof paint is a thinner-bodied product than elastomeric coating, applied more like conventional paint. It’s appropriate for metal roofs and some concrete applications, though it provides less waterproofing benefit than a full elastomeric system.

Purpose-formulated cool roof paints contain highly reflective pigments (titanium dioxide for white products, or specially engineered “cool color” pigments that reflect near-infrared radiation while appearing darker in visible light). Cool-color products can achieve meaningful reflectance in grays, tans, and terra cottas — colors that look conventional but perform significantly better than standard dark pigments.

Cost: $30–$60 per gallon; coverage depends on formulation and application method.

3. Reflective Granules (Cool Shingles)

Asphalt shingles with specially coated granules reflect more solar energy than standard granules in the same color. GAF’s Timberline Cool Series, CertainTeed’s Landmark Solaris, and Owens Corning’s Duration Cool all use infrared-reflective pigment technology that allows mid-tone shingles to achieve ENERGY STAR steep-slope ratings.

This is not a coating — it’s a property of the shingle’s granule layer. These shingles install exactly like standard asphalt shingles and are the preferred cool roof option when reroofing a steep-slope residential roof.

Performance: Reflective shingles in medium colors typically achieve solar reflectance of 0.25–0.35 — above the ENERGY STAR steep-slope threshold. They won’t perform as dramatically as a white flat-roof coating, but over a 2,000 sq ft home, the cooling impact is measurable.

Cost premium: $0.10–$0.30 per sq ft over standard shingles of the same grade. Usually modest.

4. Cool Metal Roof Coatings

Bare metal has high reflectance but low emittance — meaning it reflects well but doesn’t shed residual heat efficiently. Painted or coated metal roofs with light-colored, high-emittance finishes address both metrics and achieve excellent SRI values.

Kynar 500 (PVDF) finishes in light colors achieve SRI of 70–100 and are standard on commercial metal roofing. Residential standing-seam and metal shingle products are available in ENERGY STAR-rated colors from most major manufacturers. The finish is factory-applied and integral to the panel — not a field-applied coating.

For existing metal roofs with dark finishes, a field-applied elastomeric or specialized metal roof coating can upgrade reflectance substantially.

Real-World Energy Savings

The honest answer: savings depend heavily on climate, roof construction, attic insulation levels, and HVAC system efficiency. But the research base is solid.

The Lawrence Berkeley National Laboratory and EPA have both published estimates showing cool roofs reduce air conditioning energy use by 10–30% in hot climates. The lower end applies to well-insulated buildings; the higher end applies to buildings with poor attic insulation or direct-gain roof assemblies (like low-slope commercial buildings without attic space).

Dollar savings estimates for a typical 2,000 sq ft home:

• Hot climate (Phoenix, Miami, Dallas): $150–$400/year
• Mixed climate (Atlanta, Charlotte, Denver): $80–$200/year
• Cool climate (Minneapolis, Boston): $30–$100/year (with some heating penalty in winter)

Cool roofs work best in climates where cooling dominates. In heating-dominated climates, reflective roofs can modestly increase heating loads by rejecting solar heat that would otherwise help warm the building in winter. Net savings are still positive in most mixed climates, but the benefit is smaller.

A useful tool: the Oak Ridge National Laboratory’s Roof Savings Calculator (available online) lets you input your location, building type, insulation levels, and current roof type to estimate actual projected savings for your specific situation.

Application Process for Elastomeric Coatings

For DIY application on a flat or low-slope roof:

Preparation (Most Important Step)

1. Inspect the existing membrane for cracks, blisters, or punctures. Repair any damage before coating.
2. Clean the entire surface thoroughly — pressure wash to remove dirt, algae, and chalk. Allow to dry completely (48 hours minimum).
3. Check for ponding water areas. Standing water will fail even a good coating over time.
4. Mask or tape off edges, HVAC penetrations, and vertical flashings.

Application

1. Apply a primer coat to any repaired areas and around penetrations.
2. Apply the first coat of elastomeric coating at the manufacturer’s specified coverage rate (typically 1–1.5 gallons per 100 sq ft for the base coat). Use a long-nap roller for large areas and a brush around details.
3. Embed polyester mesh or fabric into wet coating around any cracks, seams, or repaired areas for reinforcement.
4. Allow to dry per manufacturer’s instructions (typically 4–8 hours).
5. Apply the second coat at the same coverage rate. Two coats are not optional — single-coat application produces inadequate film thickness and significantly shorter service life.
6. Allow to cure fully (usually 24–72 hours) before foot traffic.

Safety

• Work on dry days with temperatures between 50°F and 95°F
• Acrylic coatings are water-cleanup and relatively low-VOC, but still use appropriate respiratory protection and eye protection
• Silicone coatings require solvent cleanup and have higher VOC content — ventilate well

Maintenance

• Inspect annually and after severe storms
• Clean periodically (algae growth on reflective coatings can significantly reduce reflectance — a dilute bleach solution or commercial roof cleaner addresses this)
• Recoat at the first signs of chalking or loss of reflectance, typically at 10–15 year intervals

Combining Cool Roofs with Other Efficiency Measures

A cool roof works independently, but pairs especially well with:

• Upgraded attic insulation: Cool roof + R-38+ attic insulation delivers larger combined savings than either alone
• Ridge and soffit ventilation: Proper ventilation removes heat that accumulates even under a reflective surface
• Radiant barriers: A foil-faced radiant barrier stapled to the underside of rafters in hot climates can further reduce attic temperature by 20–30°F
• High-SEER HVAC: Lower cooling loads let a high-efficiency system run at its optimal point more often

Incentives and Rebates

ENERGY STAR cool roof products may qualify for:

• Utility rebate programs: Many utilities in hot states offer rebates of $0.05–$0.15 per sq ft for certified cool roof materials
• Local government incentives: Some cities with urban heat island or stormwater programs offer additional credits
• Commercial buildings: Section 179D federal tax deduction for commercial energy efficiency improvements can apply to cool roof installations

Check the DSIRE database (dsireusa.org) for current incentives in your state.

Recommended Products

For low-slope and flat roof applications:

• Henry 887 Tropi-Cool or Karnak 97AF: Well-regarded white elastomeric coatings suitable for DIY application, widely available at roofing supply houses
• GacoFlex S20: A silicone-based option with excellent ponding water resistance and longer service life

For steep-slope reroofs:

• GAF Timberline Cool Series or CertainTeed Landmark Solaris: ENERGY STAR-rated shingles in mid-tone colors that blend with traditional neighborhoods while delivering measurable reflectance improvements

For metal roofs:

• Any metal roof manufacturer’s Kynar 500 finish in a light color; field-applied options include Henry 596 Cool Roof Coating for existing metal

The cool roof concept is simple: keep solar heat off the building. The technology to do it is proven, affordable, and available right now in every major roofing product category.