Energy saving reflectant roof surfaces
California is one of the first places in the world to discover the importance of high emissivity reflecting surfaces, especially for roofs.
The concept, called “COOL ROOF, was from the outset considered an important environmental tool, both as an answer to the “HEAT ISLAND” effect and as a vehicle for saving energy. Starting from 1st January 2010, the California Energy Commission updated the energy efficiency standards of all the buildings in the American state, both residential and non-residential.
Previously, a residential “COOL ROOF” was an optional measure of energy efficiency.
Now, in most cases, roof products must be certified as such.
- ￼The phenomenon definitely came out of American universities’ research laboratories.
In New York, the citizen services and buildings departments have embraced an initiative by about 1300 volunteers, NYC °CoolRoofs” which was set up up to paint the roofs of the Big Apple white and has already painted over 150 buildings.
WHAT IS THE PROBLEM? >>
- Who has never burnt their fingers touching a dark surface in summer?
- Who has never noticed the different sensation of heat in a dark car compared to a white one?
- Who has never noticed the high temperature that asphalt can reach during a hot day, and its negative effects the evening?
The same thing happens on our roofs: a flat roof with a traditional black bituminous membrane easily reaches 80° C on an balmy sunny summer day.
Other types of traditional surfaces are equally dark and behave no differently.
This gives rise to two types of problem.
THE COLLECTIVE PROBLEM: THE HEAT ISLAND >>
THE INDIVIDUAL PROBLEM: ENERGY CONSUMPTION >>
AND THE SOLUTION… >>
Clear suggestions come from the Mediterranean…
… but scientific progress can help us to obtain more precise indications and, thus, better performance and lasting results.
THE KEY CONCEPTS
SOLAR REFLECTANCE >>
Reflectance (usually indicated with ρ) indicates the proportion of incident light that a given surface is capable of reflecting. It can have a value of between 0 and 1. The higher the value, the higher the reflectance of the roof.
EMISSIVITY IN THE INFRA-RED >>
The emissivity of materials (usually indicated with ε) is the fraction of energy radiated by that material compared to a black body at the same temperature. It is the measurement of a material’s capacity to radiate energy. A true black body would have ε = 1, whilst any real object has 0 < ε < 1 (grey body). The higher the value, the higher the roof’s emissivity.
￼”Cool” roofs are surfaces with High SRI (Solar Reflectance Index):
- High reflectance and, thus, low absorption of solar radiation
- High thermal emissivity
|SRI Limits provided for by LEED NC 2009 Italy|
|Type of roof||Slope||SRI|
|Slight||≤ 2:12||≥ 78|
|Steep||> 2:12||≥ 29|
SAVE MONEY. BENEFITS FOR THE USER:
- Reduction in summer air conditioning costs of up to 30%
- Increase in protection of waterproofing
SAVE THE PLANET. BENEFITS FOR THE ENVIRONMENT:
- Reduction of the heat island effect and, consequently, the surrounding area’s temperature
- Reduction in electricity consumption for air conditioning
BENEFITS FOR EVERYONE:
- Increase in Earth albedo, which fight against the global warming
- Pleasant visual impact
Membrane made with special bitumen modified with new generation elastomeric polymers (BPE)
High performance mono-component paint, designed to cover walkable concrete