BUILDING PERFORMANCE
What cool-roof ratings mean for an Ontario building
A product rating is not an energy bill. Understand reflectance, emittance and SRI, and separate product ratings from modelled and measured building outcomes.
A rating describes the surface. Your building determines the outcome.
A cool-roof rating helps compare how roofing materials interact with sunlight and heat. It does not tell you how much an Ontario building will save on electricity, whether a roof is suitable for restoration or whether a project qualifies for an incentive.
Solar reflectance is not an energy-savings percentage. A surface that reflects a large share of incoming sunlight does not reduce the whole building’s energy use by that same share. Walls, windows, insulation, ventilation, equipment and occupancy still matter.
Reflectance, emittance and SRI in plain language.
| Rating | Plain-language meaning | What it does not establish |
|---|---|---|
| Solar reflectance | The fraction of incoming solar energy reflected by the roof surface rather than absorbed. Initial and aged values describe different test stages. | A percentage reduction in cooling demand, total energy use or the utility bill. |
| Thermal emittance | How effectively a surface releases absorbed heat as thermal radiation. | A guaranteed roof temperature or a measured indoor comfort improvement. |
| Solar Reflectance Index (SRI) | A calculated comparison combining reflectance and emittance under standard assumptions. It is an index, not a percentage, and can exceed 100. | Building-specific savings, durability, waterproofing performance or project approval. |
The CRRC end-user FAQs explain these properties and the distinction between a rated product and a “cool roof.” The CRRC Rated Roof Products Directory is the place to check a specific product listing, including initial and aged values. Confirm the exact product and relevant listing rather than relying on an unattributed comparison chart.
Rapid Rating versus field-aged. CRRC aged values normally come from three years of real outdoor exposure. A newer product may instead show an interim Rapid Rating, marked with an asterisk in the directory: a laboratory-aged estimate that simulates three-year ageing. It is not three years of actual field exposure, and it can change when a field-aged rating replaces it.
Example: the coating used on NanoGuard commercial projects is listed under CRRC ID 1396-0001 (smooth) with initial solar reflectance 0.83, thermal emittance 0.91 and SRI 104; its 3-year field-aged values are 0.75, 0.91 and 93. An SRI above 100 means the surface stays cooler in the sun than the standard white reference surface.
Ageing and soiling change every roof surface over time, which is why the aged value matters. After three years of outdoor exposure, this coating still rates an SRI of 93.
Keep three levels of evidence separate.
Tested surface properties under defined conditions.
A prediction based on building inputs and assumptions.
Observed results, with a baseline and relevant adjustments.
A product rating describes tested material properties. A site-specific model estimates what a proposed change could do using building inputs and assumptions. A monitored outcome is based on observations from the installed project and an agreed comparison method. Moving from one level to the next requires additional evidence.
A cooler measured roof surface can be a useful observation, but it is not by itself proof of lower annual energy use. Whole-building energy comparisons need an appropriate baseline, weather context and operating information. NanoGuard’s commercial page shows how we model a building before work and document it after.
Why the Ontario building matters.
The U.S. Department of Energy cool-roof guide discusses both cooling benefits and potential heating penalties. Its general principles are useful, but a U.S. example is not an Ontario savings forecast. In a heating season, reflecting sunlight can reduce useful solar heat gain; that tradeoff belongs in an annual assessment.
- Roof area and assembly: how much roof covers conditioned space, and how the layers are configured.
- Insulation and air leakage: how strongly roof surface conditions affect the occupied building.
- Operation and HVAC: occupancy schedules, internal heat gains, heating fuel, equipment efficiency and control settings.
- Weather and exposure: local sun, temperatures, shading and seasonal conditions, including snow cover.
- Roof condition: moisture, drainage, repairs and membrane compatibility may determine whether a coating is appropriate at all.
The NRCan hospital retrofit guide reinforces a building-system approach to energy decisions. A hospital’s ventilation and operating demands differ from those of a warehouse or small office; its guidance should not be used as a generic roof-only savings claim.
A checklist for a useful review.
- Location, building use, conditioned area and approximate roof area.
- Roof assembly, insulation information, condition, drainage and repair history.
- Available utility history, heating fuel, HVAC details and operating schedules.
- The decision being considered: restoration, heat-load reduction, comfort, solar planning or capital timing.
- The exact proposed product/system and its current rating documentation.
- Whether modelling is appropriate, which assumptions need checking and what would be measured after installation.
We record unknowns as unknowns and show you the assumptions behind every model.
Get an answer for your building, not a generic number.
Send us the building. We assess the roof, model it with Roovie and give you a building-specific answer. Read how to plan a commercial roof pilot before defining before/after evidence, or bring your project to the partner pilot brief.
Sources & further reading
- CRRC End-User FAQs: surface properties and rating interpretation.
- CRRC Rated Roof Products Directory: verify an exact product listing.
- DOE Guide to Cool Roofs (PDF): climate, cooling and heating tradeoffs.
- NRCan Hospital Retrofit Guide (PDF): building-system context, not a roof savings estimate.