Emissiv’s radiative-cooling coating reflects 95% of sunlight and emits 95% of thermal heat for an opaque surface. This page shows what those measured optics mean on a roof, and how the map turns them into opportunity.
By day the coating works first as a mirror: 95% of incoming sunlight never lands as heat. All day and night it also works as a radiator, emitting heat strongly to the sky. Scrub the time slider below and the roof follows the balance between sun in, heat out and wind.
A clear UK summer day. The dark roof today peaks near 66 °C. The coated roof stays at or below the air temperature for all 24 hours. Plain white paint is shown too, in the interest of honesty.
Surface temperature, °C. Curves are modelled from measured coating optics: 95% solar reflectance and 95% thermal emittance, opaque. The existing dark roof is modelled from measured albedo plus assumed stock-roof emittance.
Coated and plain white sit within ~1 °C at the day’s peak. By day, reflectance does the work: any high-reflectance roof wins, the coating is not special yet.
After sunset the engines separate. The coating keeps shedding heat through the window while white paint, radiating into a partly-closed sky, lags behind.
The coated roof stays at or below air temperature all 24 hours. On the same day the dark roof peaks 41 °C above the air.
Solar Reflectance Index is the industry shorthand for “how cool a roof surface runs”. It is useful because it combines reflectance and emittance, not colour alone, and the map uses the ASTM E1980 balance for roof SRI.
For the coating, SRI is only the start. The commercial question is roof-specific: how dark is the roof today, how large is it, what building sits underneath, and does it carry cooling demand? That is why the product leads with heat rejected, peak-temperature cut, and tiered cooling savings rather than a single compliance number.
The coating optics used in those calculations are simple and strong: 95% solar reflectance and 95% thermal emittance for an opaque film. Existing roof-stock emittance is the weaker input, assigned by material because it is not measured from Sentinel-2.
Nothing on this page is asserted. Each number is one of three things, and we say which.
95% thermal emittance for the coating optics, the engine that lets the surface radiate heat to the sky.
95% solar reflectance. The coated-roof maths uses an opaque 0.95 reflectance input. The full cured-film spectrum is in progress, but the product parameter is now wired into the roof opportunity calculation.
These curves. A clear-sky UK summer day, dew point 12 °C, a humidity-aware Berdahl & Martin sky, and ASTM E1980-style convection. Quasi-steady surface temperatures, half-hourly.
Existing roof-stock emittance, assigned by material because Sentinel-2 does not measure thermal emittance. Bare metal is hedged lower than tile, slate or membrane.
The still-air (hc 2) numbers are upper bounds. The model is radiative-only, with no coupling to the roof’s thermal mass, so it over-states cooling when convection is weak. Trust the breezy case for deployment.
A reflective roof also rejects weak winter sun that was giving the building free heat. We bounded that tradeoff with each city’s own monthly sunlight (PVGIS): at most ~11% of the cooling saving under gas heating, ~12% with a heat pump. An upper bound, stated rather than hand-waved.
The same engine that draws these curves prices them, per roof, against the real grid.
For every dark roof the engine computes the solar heat a 95% coating would bounce away each year: pure physics, reflectance times the roof’s own measured sunlight (PVGIS, per location) times its area. A single large dark deck can reject thousands of MWh over a coating’s life.
On top of the sunlight it reflects, the coating actively sheds heat to deep space through the 8–13 µm sky window. The two-band model puts this at ≈ 68 W/m² net at ambient under a clear UK sky; annualised at a deliberately conservative 0.18 clear-sky duty (cloud closes the window) it lands at ≈ 13% of the reflected solar load in MWh/yr. This is separate from and additional to the heat rejected above, and is not priced in the £ below: it shows up as passive cooling, sub-ambient nights and comfort, not a bill. Modelled, clear-sky only (cloud closes the window); in winter it adds to the heating tradeoff already bounded. Full physics in the radiative-cooling simulator.
Where a building is air-conditioned, rejected heat becomes electricity not bought. The map uses a three-tier ladder: EPC/SBEM cooling demand where present, a BEES building-type benchmark where use implies cooling, and physics-only with no pounds where there is no cooling signal. For a real building we replace the estimate with your metered cooling load, so the saving becomes your own arithmetic.
Avoided electricity is converted to CO₂ using the National Grid’s live carbon intensity, fetched at the moment you look, not a stale yearly average. Greener grid hour, smaller number: the figure is honest by construction.
See it priced on a real roof: open the map, click any dark roof, and press “Apply 95% coating”. The full chain from pixel to pound is on How it works.
The coating is the answer. The map shows where the question is loudest: the dark roofs running 40 degrees over the air.