Excessive heat: the importance of the sun reflectance of the roof
To evaluate the thermal impact of a cover in the surrounding environment, you need to know the following factors:
- The reflective of a surface (usually indicated with ρ) indicates the proportion of accident light that a given surface is able to reflect and can take values from 0 to 1. The high the value is the higher the reflective of the roof.
- The emissiveness of a material (usually indicated with ε) is instead the fraction of energy radiated by that material with respect to the energy radiated by a black body that is at the same temperature. It therefore measures the ability of a material to radiate energy. The higher the value the higher the emissiveness of the roof.
- The solar reflection index or SRI (Solar Reflectance Index) is the parameter that combines reflective and emissive values and expresses the ability of a material to reject solar heat. More reflectance and emissiveness have high values, the higher is the SRI.
From these definitions it can be deduced that a reduced solar absorption value and a high emissiveness value are two characteristics that allow a material not to overheat and disperse a lot of energy by radiation.
The concept of “Cool Roof”
To limit the energy needs of the buildings, the concepts of Cool Roof and Cool Materials come into play. The term Cool Roof (literally “cold roof”) means a cover system that can offer high sun reflectance and high thermal emissiveness: the reference parameter is Sri.
Through a good use of the intrinsic radiative properties of materials it is possible to “limit energy needs for summer air conditioning and contain the internal temperature of the environments, as well as to limit urban scale overheating” (as per text of the Ministerial Decree 26.06.2015). This means that a roof that reflects a high amount of solar energy and disperses less heat is a roof with high performance and complies with what is prescribed as a minimum requirements decree.
Solutions for the reduction of the “heat island” effect
Saint-Gobain Italia offers a range of solutions for energy saving and high solar reflectance index, in particular the Saint-Gobain Roof System California BT2 system: certified solution BRoof(T2) from third party for high SRI floors (Solar Reflection Index).
The solution is made up of a first Bituver S -30 4 mm P -Range, consisting of an elastomeric membrane with special BPE compound and cold flexibility -30 ° C. The second seal element is the Elastomeric membrane with high SRI with special BPE compound, glued on fire, Bituver Megaver California. The membrane is covered with a predernized clumsy aluminum foil with reflective white paint, upon treatment with very high technology aimed at improving adhesion and durability.
With this Saint-Gobain Italia solution, it offers the market the only waterproofing membrane for covers with the following SRI values, certified by third party:
- Certified SRI values: 96% (new)
- Certified SRI values: 80% (subjected to aging)
Solutions against hail
Saint-Gobain Italia research and innovation in the field of modern construction materials-which combine living comfort and sustainability-now offer a wide range of products and isover branded solutions dedicated to the roofs.
The Bituver line, which includes elastomeric and elastoplastomeric membranes with bitumenic technology®offers advanced solutions for roof protection. These products guarantee excellent waterproofing and resistance to the impacts of hail. Among them, some are tested for the determination of hail resistance according to the EN 13583 standard, ensuring not only the effective protection of the roofs but also the possibility of restoring their integrity after any damage.
An example in this sense is Bituver Fleximatan elastomeric membrane with Armor in TNT of continuous wire polyester reinforced with fiberglass wires. Bituver Renoveron the other hand, it is a double mixing membrane ideal for the renovation of old and deteriorated membranes. The lower side, made with a specific elastomeric compound SBS guarantees high grip, while the upper side in APAO compound allows for upper application efficiency.
Among the complete solutions of thermo-acoustic insulation proposed by Saint-Gobain Italia we mention Saint-Gobain Roof System Ice Protection: a flat coverage with mineral insulation and waterproofing membrane in double layer. Bureau Veritas He carried out a technical certificate of conformity of the Saint-Gobain Roof System Ice Protection waterproof system to the UNI 8178/2: 2019 standard (continuous covers design indications). In addition to the insulating layer consisting of the G3 Roofine Isover Superbac Panel, the sealing element, used as a layer to finish, consists of the elastomeric membrane Bituver Fleximat 4 mm Mineral which, thanks to the special BPE compound, guarantees cold flexibility up to -25 ° and has been subjected to hail resistance tests.
Solution with continuous polyurethane liquid membranes
Saint-Gobain Italia, with the Weber brand, also proposes ETA certified solutions: these are solutions with polyurethane systems that form a continuous layer, without interruptions, equipped with high elasticity and resistance. Polyurethane liquid membranes, being equipped with high performance characteristics, increase the durability of the structure they protect, managing to indulge it in its deformations
Find out more in the new edition of the Roofing catalog 2025.
