Cool roof or heat-reflective tiles are light-coloured tiles laid on flat roofs and terraces to reflect sunlight and release absorbed heat. A cooler roof surface means less heat passes into the rooms below. Their performance is measured and compared using the Solar Reflectance Index, or SRI.
They are usually white or very pale glazed tiles. In hot countries, including India, they are commonly laid over roof slabs as a simple way to cut heat gain.
What SRI measures
SRI combines two properties of a surface:
- Solar reflectance: the share of sunlight the surface reflects rather than absorbs, on a scale of 0 to 1.
- Thermal emittance: how well the surface gives off the heat it does absorb, also on a scale of 0 to 1.
SRI is calculated from both, under the method in ASTM E1980. A standard black surface scores about 0 and a standard white surface about 100. Very reflective surfaces can score above 100. Higher means cooler.
Solar reflectance and emittance are each measured to their own test methods by a laboratory. The report should give both values and the SRI calculated from them.
Where SRI targets come from
Green building schemes and some building codes set minimum values. For example, the LEED v4 heat island credit asks for an initial SRI of at least 82 on low-sloped roofs and 39 on steep-sloped roofs, or aged values of 64 and 32. Other schemes and codes set their own values, so check what your project needs.
Aged values matter because roofs get dirty. Dust, soot and growth lower reflectance over time. In the US, the Cool Roof Rating Council publishes initial and aged ratings for roofing products. Ask whether your market expects a rating from such a body.
Ceramic tiles as cool roofs
Glazed ceramic tiles have useful traits for this job. A white fired glaze is stable in sunlight and does not chalk like some paints. A glazed surface is fairly easy to clean, which helps keep reflectance up.
The limits are practical. A tiled roof adds weight to the slab. Joints and edges must be watertight, or the roof will leak even if it stays cool. Tiles on a roof must also resist thermal shock and, in cold climates, frost. Our guide on frost resistance covers that test.
Treat claims with care
Catalogues often claim that a tile lowers roof or room temperature by a set number of degrees. That depends on the climate, the building, the insulation and the measurement. Without a report, it is a sales line.
What you can rely on is a laboratory report for the exact product, giving solar reflectance, thermal emittance and SRI, with the test methods named. Check that the report matches the tile's colour, glaze and surface. A matt or textured version of the same white can score differently from a glossy one.
What to put in your order
- Solar reflectance, thermal emittance and SRI from an accredited laboratory, with methods and date.
- Water absorption to ISO 10545-3, and frost resistance to ISO 10545-12 where it freezes.
- Slip resistance if people will walk on the roof terrace.
- One batch and one shade, since whites show shade differences clearly.
For terraces that people use, also see tiles for terraces and balconies.
Next step
We check SRI and other reports against the exact tile you are buying, and supervise production and loading. To plan a cool roof range, book a free sourcing review.