Innovative roof cool roofs by T.Maniammai & T.M.Supraja

What is a cool roof ? A cool roof reflects the sun’s heat and emits absorbed radiation back into the atmosphere.

Properties of cool roof high solar reflectivity- degree to which a roof reflects heat high emissivity- roof's ability to give off its absorbed heat.

Types of cool roof Inherently cool roof Coated roofs Green roofs

Inherently cool roofs Roofs made of materials that are inherently cool. Coatings are not provided Metal roofs and asphalt shingles are commonly used

Asphalt shingles Similar to rolled asphalt roofs roofing granules pressed into the shingle while it is hot (and soft) The roofing granules are 1 millimeter-sized stones (e.g., of crushed granite)

Roofing tiles Tile roofs often have enhanced air circulation compared to other roofing types Roofing tiles can be ceramic or fabricated from cement concrete. Some of the lighter types use fibers (e.g., cellulose) added for strength.

Metal roofs Aluminum and steel may have a solar reflectance of 60 % and low emittence The reflectance and emittance of metals are very sensitive to the smoothness Even a thin white coating "hides" the low emittance of the metal

“White” is new green White paint serve good Highly reflective coating Economical Easily available Paint is easy to apply and dries soon

White elastomeric solar coating An elastomer is a polymer with the property of viscoelasticity Soft and are amorphous polymers existing above their glass transition temperature Examples: acrylic polymers, polyurethane

THE BETTER ELASTOMER POLYURETHANE……… Solvent based. strong tensile strength. exhibit greater adhesion. often used with metal roofs. At high solids levels meet VOC regulations.

WHY ACRYLIC IS NOT PREFERED Not prefered for cold climate as it gets affected when comes into contact with water The ASTM D-6083 standard defines the performance properties for an acrylic coating. Should be used only when there is proper drainage.

Coating is better The solar reflectence of asphalt is only 20 % whereas the elastomeric coating has a solar reflectance of 80% and hence it is prefered Asphalt is prefered for sloped roofs

Selection of coating Depends on substrate Age of roof Climate

Surface preparation Remove dirt and scum Pressure washing Scratching the surface Application of primer In metal roofs if there is corrosion use inhibitors Coating acts as sealant for water leaks

Substrate with coating

How to apply ?

Failure patterns

Prevention of failure Weaknesses of the original roof system must be corrected roof should be made watertight Weather conditions during the project installation must be monitored. The roof should drain properly Roof should be maintained and coating should be replaced periodically

Green roofs Making the roof green………. Improved air quality as the plants absorb and convert carbon dioxide to oxygen Long lifespan - some green roofs in Europe have lasted more than 40 years Excellent insulation Cooled surrounding environment increases the area of habitat for wildlife such as birds and insects

Green roofs

A special note on TiO2 provides opacity increase solar reflectance reduce surface temperatures absorbs UV radiation

SELF CLEANING Photoactive TiO2 particles in the binder promote free radical attack at the surface of the system Inorganic dust remains but “glue” can be destroyed therefore reducing the adhesion force between the particles and the surface .When it rains these particles are washed away rejuvenating the surface.

Vermiculite Vermiculite is a natural mineral that expands with the application of heat. The expansion process is called exfoliation . It has low thermal conductivity ,light weight, not flammable. Applied as weathering course by mixing with equal weight of cement and sufficient water

Policy and Code Bodies ECBC--‐2007 --‐ Bureau of Energy Efficiency (BEE) LEED --‐ Indian Green Building Council (IGBC) GRIHA --‐ The Energy and Research Institute (TERI/ MNRE) Ministry of Environment and Forests, Government of India--‐ MoEF – Bureau of Indian Standards (BIS) The Energy Conservation Building Code (ECBC)

Benefits of cool roof Reduce building heat-gain, as a white or reflective roof typically increases only 5–14 °C above ambient temperature. Create 15–30%  savings on summertime air conditioning expenditures. Enhance the life expectancy of building’s cooling equipment.

Benefits Improve thermal efficiency of the roof insulation Reduce the demand for electric power Reduces greenhouse gas emissions. If all urban, flat roofs worldwide were whitened, the reduction in carbon emissions would be 24 Gigatonnes, or equivalent to taking 300 million cars off the road for 20 years.