Cool Roof Calculator
Energy savings from reflective roofing surface.
About this calculator
A cool roof coating reduces cooling costs by reflecting more solar energy (a higher Solar Reflectance Index) than the existing dark roof, but that same reflectivity slightly reduces free passive-solar heating in winter, so this calculator nets the two effects against each other. Net Annual Savings only responds to the four cost/SRI inputs -- Current Roof SRI, New Cool Roof SRI, Annual Cooling Cost, and Annual Heating Cost -- and never to Roof Area or Coating Cost ($/sqft), which instead determine Installation Cost and, from there, the payback period.
Whether the coating is worth it net of the winter penalty depends on the balance between your cooling and heating bills: cooling savings scale off Annual Cooling Cost at up to a 35% reduction factor, while the heating penalty scales off Annual Heating Cost at up to a 7% factor, so a building with a large cooling bill and a modest heating bill sees Net Annual Savings rise reliably as the SRI improvement grows -- but a building with the opposite balance (small cooling bill, large heating bill) can see the winter penalty erode or even reverse that trend, which is why this tool is most useful for buildings that are meaningfully cooling-dominated. Payback Period only calculates when Net Annual Savings is positive; it stays at zero otherwise rather than showing a nonsensical negative payback.
Inputs
Results
Net Annual Savings ($)
$273.00
How to Use This Calculator
- Enter the roof area (sqft) and current roof SRI (Solar Reflectance Index).
- Set the target cool roof SRI (white coatings: 82+, white TPO: 78+, white metal: 90+).
- Enter your current annual cooling cost ($) and annual heating cost ($).
- Review annual cooling savings, heating penalty, and net annual savings.
- Check peak temperature reduction (F) -- every 10F reduction lowers cooling load ~5-10%.
How the result changes with New Cool Roof SRI
| New Cool Roof SRI | Net Annual Savings ($) |
|---|---|
| 41 | $93.00 |
| 62 | $185.00 |
| 100 | $353.00 |
What each input means
- Roof Area (sqft)
- Total roof surface area in square feet.
- Current Roof SRI
- Solar Reflectance Index of existing roof. Dark asphalt ~20, aged white ~50.
- New Cool Roof SRI
- SRI of proposed cool roof coating. White elastomeric ~78-90, metal ~25-70.
- Annual Cooling Cost ($)
- Current annual air conditioning electricity cost.
- Annual Heating Cost ($)
- Current annual heating cost (gas or electric).
- Coating Cost ($/sqft)
- Cost per sqft for cool roof coating application. Elastomeric ~$1-3/sqft.
What each result means
- Net Annual Savings ($)
- Annual energy savings after subtracting winter heating penalty.
- Cooling Savings ($/yr)
- Estimated annual reduction in cooling costs.
- Heating Penalty ($/yr)
- Increased winter heating cost from roof reflectivity.
- Peak Temp Reduction (°F)
- Estimated peak roof surface temperature reduction.
- Installation Cost ($)
- Total cost to apply the cool roof coating.
- Payback Period (years)
- Years to recoup coating cost through energy savings.
- 20-Year Net Savings ($)
- Total savings over 20 years minus installation cost.
How this is calculated
Worked example, using the default values
- Identify Input Parameters4 parametersRoof Area (sqft) = 2000, Current Roof SRI = 20, New Cool Roof SRI = 82, Annual Cooling Cost ($) = 1500 = 6 input(s) provided
- Calculate Net Annual SavingsNet Annual Savings = annualCoolingSavings - annualHeatingPenalty273 = $273
- Calculate Cooling SavingsCooling Savings = annualCoolingCost * coolingReductionPct326 = $326
- Calculate Heating PenaltyHeating Penalty = annualHeatingCost * heatingPenaltyPct52 = $52
Engine last updated . Checked against 2 independently-derived tests — how we verify calculators. Built by Paul Gunder, a software engineer, not a licensed financial, medical, or legal professional.
Frequently Asked Questions
Where do the 35% cooling-savings cap and 7% heating-penalty cap in this calculator come from?
They're simplified stand-ins for a range the Department of Energy publishes for cool roof cooling-energy reduction, roughly 10-30% depending on climate and building type, paired with a smaller offsetting winter heating penalty that's well documented in cool-roof research but varies more by region than the cooling benefit does. This calculator picks single representative caps rather than a full climate-zone lookup table, so treat the output as a reasonable planning estimate, not a substitute for a location-specific energy model or a utility rebate program's own calculation.
Why doesn't a bigger reflectivity improvement always mean bigger net savings?
Cooling savings and the winter heating penalty both scale with the same SRI improvement, but off different cost bases -- up to 35% of your Annual Cooling Cost versus up to 7% of your Annual Heating Cost. For a building with a small cooling bill and a large heating bill, the winter penalty can grow faster than the cooling benefit, shrinking Net Annual Savings even as reflectivity improves.
Does the coating cost per square foot affect my annual savings?
No -- Coating Cost ($/sqft) only determines Installation Cost ($), used to calculate Payback Period (years) and 20-Year Net Savings ($). It has no effect on Cooling Savings ($/yr), Heating Penalty ($/yr), or Net Annual Savings ($) itself.
My building has high heating bills and low cooling bills -- is a cool roof coating still worth pricing out?
Run the numbers before assuming it isn't, but go in skeptical. Cooling savings scale off Annual Cooling Cost while the heating penalty scales off Annual Heating Cost, so a heating-dominated building sees the winter penalty grow relative to the cooling benefit it's offsetting. Payback Period (years) is set to zero rather than showing a negative number whenever Net Annual Savings isn't positive, which is this calculator's way of flagging that a cool roof coating may not pay back at all for your specific cost balance.
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