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Cool roofs: do solar reflective coatings cut cooling costs?

Updated 23 October 2026 · SEO Dons Editorial

Cool roof claims are easy to find and hard to check. This guide separates what research bodies have measured from what a supplier's brochure implies, using only dated, attributed sources. It stays with the roof surface. Choices about how a building is heated or cooled belong to the building services designer, and a reflective finish does not repair a leaking roof, a point taken further in the guide to roof coatings and liquid membranes.

How do solar reflectance and thermal emittance work?

A cool roof absorbs less of the sun's heat than a conventional one. The US Environmental Protection Agency (EPA), on a page last updated on 18 June 2026, says high solar reflectance is the most important characteristic and that high thermal emittance, which is how well the roof sheds the heat it does absorb, also plays a role, particularly in warm, sunny climates. Lawrence Berkeley National Laboratory's Heat Island Group defines thermal emittance as the efficiency with which a surface cools itself by emitting thermal infrared radiation, and says a cool roof should have both properties high.

Reflective finishes come in several forms. The EPA lists liquid-applied roof coatings with light or cool colours, and single-ply membranes with light or cool-coloured pigments, among low-slope cool roof products. So a "white roof membrane" and a "solar reflective coating" are two routes to the same surface property.

How much cooler does a reflective roof surface get?

Berkeley Lab states that on a typical summer afternoon a clean white roof reflecting 80% of sunlight will stay about 31°C (55°F) cooler than a grey roof reflecting only 20%. The page adds that this is calculated under the standard summer afternoon weather specified in ASTM E1980-11, which is a defined test condition and not a UK summer day. Treat the 31°C as a measure of what reflectance can do under strong sun, not a prediction for a British warehouse in July.

Illustrative arithmetic only: a surface reflecting 20% of sunlight absorbs about 80% of what reaches it, while one reflecting 80% absorbs about 20%, a quarter as much. Real surface temperatures also depend on emittance, wind, shading and what lies beneath.

Do reflective roofs cut cooling costs in the UK?

The UK evidence is thinner than the marketing. The most relevant published study found is Kolokotroni, Gowreesunker and Giridharan, "Cool roof technology in London: an experimental and modelling study", Energy and Buildings 67 (2013), held in Brunel University's research archive. Its authors monitored a naturally ventilated London office before and after a reflective paint was applied to its flat roof during the summer, and report that internal temperatures were reduced after the application of the cool roof. They then calibrated a building model and varied reflectivity, roof insulation and ventilation rate.

The modelled results are the cautionary part. Cooling demand was significantly reduced, but heating demand increased, and total energy savings varied between 1 and 8.5% relative to an albedo of 0.1 for the same conditions. Modelled thermal comfort could improve by an average of 2.5 °C (an operative temperature difference for a change of 0.5 in albedo), but heating demand could rise by 10% at a ventilation rate of 2 air changes per hour. The authors concluded that in temperate climates the type, operation and thermal characteristics of the building should be considered carefully. That is one office, modelled, so it shows a range and a trade-off. It is not a rule for sheds, warehouses or retail units.

The EPA says the so-called heating penalty is typically offset by summer cooling savings, and Berkeley Lab says the same for most of the United States. A separate US simulation of commercial building prototypes also found that, for a commercial building, the decrease in annual cooling load is typically much greater than the increase in annual heating load. Those are US findings, and the London study shows why they should not be carried across unchanged to a colder, cloudier climate. The EPA does cite one UK study that found cool roofs, implemented across a city, could offset 18% of heat-related mortality associated with the heat island effect. That is a public health result for a city, not a cost result for one building.

Where is the effect larger and where is it small?

Published studies agree that the answer depends on the building. The Brunel authors say the relative benefits depend on the construction of the building, external weather conditions and use of the building. The EPA says effective insulation and energy-efficient design can also reduce impacts of the winter heating penalty, and advises owners to consider insulation and air sealing alongside a cool roof. None of the sources cited here isolates single-storey sheds or rooftop plant, so a claim that a particular shed or plant deck will benefit most needs a building-specific calculation behind it. Ask any supplier quoting a saving for the inputs: insulation, cooling or ventilation, occupancy hours and location.

What happens as the surface gets dirty?

Reflectance does not stay at the brochure value. Berkeley Lab notes that roof reflectance is rated when new and after three years of outdoor exposure, and its laboratory ageing method uses a soiling mixture of dust, soot, particulate organic matter and salts to reproduce natural soiling. The EPA says ongoing costs may include periodic maintenance to keep the roof clean and maximise its reflectance, particularly for low-sloped roofs. For a flat commercial roof that means cleaning belongs in the maintenance plan, covered in the guide to commercial roof cleaning.

What should you check before specifying a reflective finish?

  1. Ask for both initial and aged solar reflectance and thermal emittance from a recognised rating, and treat a new-surface figure alone with caution.
  2. Check that the roof beneath is sound and dry. A reflective finish on a failing covering hides the problem; the commercial flat roof refurbishment page explains why the core sample comes first.
  3. Ask how the finish affects the fire classification of the whole build-up, as set out in the BROOF(t4) guide.
  4. Consider glare. Berkeley Lab notes that glare from a bright white or silvery roof on a low-rise building may disturb occupants of taller neighbouring buildings.
  5. Check whether the work counts as renovation for energy rules, using the building regulations guide. A reflective finish changes how much sunlight is absorbed, which is a separate matter from insulation.
  6. If a liquid membrane is on the table, compare resin types in the PMMA, polyurethane and GRP guide.

You can send roof details through the form on the refurbishment page to compare reflective options on your own roof.

Sources

Common questions

Do cool roofs work in the UK?

A reflective surface does run cooler in sun, and a London office study found internal temperatures fell after reflective paint went on. Energy savings were modelled at 1 to 8.5% in that case, with a winter heating penalty, so the benefit depends on the building.

Will a reflective coating stop a roof leaking?

No. Reflectance changes how much sunlight the surface absorbs, not whether the covering keeps water out. A reflective finish on a failing roof hides the problem, so establish the condition of the covering and insulation first.

How often does a reflective roof need cleaning?

None of the sources cited gives a UK interval. The EPA says periodic maintenance to keep the roof clean helps maximise reflectance, particularly on low-sloped roofs, so include cleaning in the maintenance plan and ask the supplier for its guidance.

Is a white membrane the same as a reflective coating?

Both aim at high solar reflectance, and the EPA lists coatings and single-ply membranes among low-slope cool roof products. They differ in how they are applied and certified, so compare aged reflectance and the certificate, not just colour.

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