Cool roofs are surfaces that are highly reflective and resistant to heat transfer. In hotter climates like that of Barcelona, cool roofs can offer immediate and long-term benefits including: lowering air conditioning costs; mitigating the urban heat island effect; reducing air pollution and greenhouse gas emissions; and offsetting of the warming impact of greenhouse gas emissions.
When sunlight falls on a white roof much of it is reflected and passes back through the atmosphere into space. When sunlight falls on a dark roof most of it is absorbed and converted into much longer wavelengths that we call "heat" which cannot pass back through the atmosphere because they are absorbed by the greenhouse gases. The atmosphere is transparent to sunlight but opaque to heat, which is why white roofs help cool the planet and dark roofs warm the planet.
While it is true that cool roofs are mostly associated with white roofs, they come in a variety of colors and materials and are available for both commercial and residential buildings. In fact, today's "cool roof" (reflective to visible light and opaque to heat) pigments allow metal roofing products to be EnergyStar rated in dark colors, even black.
Cool roofs are an order of magnitude cheaper than installing green roofs while providing many of the same benefits to the building. However, it does not provide many of the benefits of green roofs. A 2012 study by researchers at Concordia University included variables similar to those used in the Stanford study (e.g., cloud responses) and estimated that worldwide deployment of cool roofs and pavements in cities would generate a global cooling effect equivalent to offsetting up to 150 Gigatonnes of carbon dioxide emissions - enough to take every car in the world off the road for 50 years.
A photocatalytic roof has a semiconductor material that destroys pollutants like NOx (a principal offender in Barcelona's air) and renders them as harmless salts. The most common semiconductor material is titanium dioxide. Titanium dioxide has a high photo catalytic efficiency, low cost, relative stability and low toxicity.
Reducing pollution and lowering carbon dioxide emissions is as easy as applying a couple of coats of paint. Contact Eixverd!