What happens to reflectivity and emissivity after half the lifetime of the roof (meaning after more than 3 years)?
Emissivity of most products will stay about the same for the life of the product. The exception is unpainted metal roofing, which starts off very low, but increases as an oxide layer forms on the panels. This aged value, however, is still much lower than most other materials or painted metal. Reflectivity typically goes down as the material gets dirty and weathered. White membrane roofs get darker and lower in reflectivity in 3 years. Allowing these products to be washed before measuring the aged reflectivity gives unrealistically high aged reflectivity values. Metal panels also lose reflectivity as they get dirty, but they typically don’t get as dirty as other materials and don’t lose reflectivity as fast. Airborne dirt and contaminants are much more easily washed off the smooth metal surfaces by natural rainfall.
Related Questions
- Remember that emissivity and reflectivity both play a part in the surface temperature of a roof. Back to Top Why does a white prepainted metal roof have a much higher emissivity than an unpainted metal roof?
- Can roof coatings be used to meet the emissivity and reflectivity standards?
- What happens in the Lifetime Movie Dangerous child?
