Metal roofing installation is a simple process that masks some highly complicated heat exchanges. A variety of materials are used to minimize heat intrusion into attics, including foil insulation. In order to get the most out of these materials, they must be installed correctly. Foil insulation with only one shiny side should be placed between roof decking and the metal roof with the shiny side facing up. However, if you are installing the insulation to the rafters in the attic, place it with the shiny side facing down to discourage dust accumulation.
During the day the sun's radiation heats the roof, allowing the metal to conduct that radiation to the inside of the attic and heats the whole attic. Radiant barriers like foil insulation work by reflecting invisible heat waves away from the surfaces they are insulating, minimizing attic heat gain. Cooler attics mean cooler insulation, and cooler insulation functions at its best.
Radiant Barrier Materials
Reflective insulation is made of a variety of materials in a few styles. These systems are composed of one or two sheets of aluminum and an insulate material. Single-sided systems are backed with low emission materials, like kraft paper, plastic films, polyethylene bubbles or cardboard. Double-sided systems are foam sheets encased in an aluminum envelope.
Rating Radiant Barriers
Radiant barriers are rated based on their emissivity and reflectivity. Emissivity refers to the ratio of absorbed energy being emitted from the surface in question as compared to the energy emission of a black surface. On radiant barriers, this is expressed as a number between 0 and 1. Reflectivity refers to the amount of energy that is actually reflected by a material. This is a number between 0 and 100. When shopping for radiant barriers, always select the material with the highest number in both categories.
Correct installation is vital to proper functioning of any kind of foil insulation used in conjunction with a metal roof. You should attach the foil insulation directly to the roof deck with the shiny side up, with seams sitting snugly beside one another. Add furring strips to the roof to create a 3/4-inch gap between the deck and the metal roofing. Attach the metal roofing to the furring strips. The air gap optimizes the heat exchange between the foil and the roof.