What SRI Means for Your Roof
Solar Reflectance Index measures how well a roofing material rejects solar heat on a scale of 0 to 100. A standard black asphalt shingle scores around 20-30. A white TPO membrane scores 80-90. The higher the number, the less heat your roof absorbs and transfers into your building.
In Houston, this isn’t academic. A roof with an SRI of 25 gets much hotter on a July afternoon than a roof with an SRI of 78 under the same conditions. That extra heat raises the cooling load on your building — and in a city where AC runs 7 months a year, it adds up fast.
SRI by Roofing Material
White TPO/PVC membrane: SRI 80-90. The top performer. This is why TPO dominates commercial flat roofing in Houston.
Light-colored metal (Galvalume, white Kynar): SRI 60-75. Standing seam metal with a light finish is the best-performing residential option.
Stone-coated steel (light colors): SRI 40-55. The ceramic granules reflect more than standard shingles but less than bare metal.
Architectural shingles (light colors): SRI 25-35. Standard “cool color” shingle options from Owens Corning and Owens Corning improve on dark shingles but still absorb significant heat.
Dark asphalt shingles: SRI 15-25. The worst performer. Common on older Houston homes and the reason many attics run so hot.
Why It Matters for Houston Buildings
Energy codes in Houston increasingly reference SRI for commercial roofing. The 2021 IECC requires cool roof materials on low-slope commercial roofs in Climate Zone 2 (which includes Houston). That effectively mandates TPO, PVC, or light-colored metal on any new commercial flat roof.
For residential, there’s no SRI mandate yet. But choosing a higher-SRI material still pays off. The less heat the roof absorbs, the less of it your AC has to work to remove.
The Trade-Off
Higher SRI usually means lighter colors. Not every homeowner wants a white or light gray roof. The good news is that cool-roof technology is improving — Owens Corning now offer “cool color” shingles in medium tones that score SRI 25-35 instead of the typical 15-20 for dark shingles. Not as good as metal, but a meaningful improvement.
Want to know the SRI of your current roof or compare options? Contact us and we’ll walk through the numbers for your specific situation.
Solar Reflectance Index (SRI)
SRI rates how well a roof keeps cool in the sun. It blends two lab-measured numbers: solar reflectance (R) – how much sunlight bounces off – and thermal emittance (E) – how quickly the surface re-emits heat. Higher SRI = cooler roof → lower attic temps & energy bills.
| Material | Solar Reflectance (R) | Thermal Emittance (E) | SRI |
|---|---|---|---|
| White TPO membrane | 0.79 | 0.90 | 98 |
| Cool-coated metal (light gray) | 0.55 | 0.85 | 72 |
| Unpainted Galvalume® | 0.55 | 0.10 | 46 |
| Charcoal asphalt shingle | 0.12 | 0.85 | 21 |
Estimate your roof’s SRI
*Uses a simplified ASTM E1980 approximation for web demo purposes.