Radiant insulation works by reflecting away radiant heat and reduce the costs of air conditioning. The reflective insulation is available in a number of forms, most notably as rolls of foil sheets or as metal shingles. When properly installed, radiant insulation can block heat from the sun’s rays and keep the home cooler.
Heat can be transmitted by three methods. Conduction passes heat from one solid object to another through contact. Convection carries heat through a fluid medium, rising and falling with the temperature until the heat is spread evenly. Radiation is the third method of heat transfer, passing in a straight line from a heat source and warming any object in its path.
Homes receive radiant heat in the form of sunlight, which heats up the roof. Heat passes into the attic’s interior by conduction. After the inner surface of the roof has been heated, this surface radiates heat into the attic. Radiant insulation blocks this heat, reflecting it back to the roofing.
Although most commonly found as sheets of plastic foil, radiant insulation is available in a wide variety of forms. Metallic shingles, reflective chips and foil-covered boards are also commonly used. Some conventional insulation also comes with a reflective surface, blocking all forms of heat transfer.
Effective insulation from radiant energy depends on three factors: the insulation’s reflectivity; its emissivity, or the amount of heat that passes through; and the angle of deflection. High reflectivity and low emissivity are ideal. The angle is dependent upon installation, and for best results, should be parallel to the roof.
Often, radiant insulation is affixed to the inner rafters, lining the roof. This not only places the insulation at the best possible angle, it also prevents dust from gathering on the surface. Dust and debris makes the insulation less reflective and less effective.
Attaching radiant insulation directly to the roof is not effective. If the roof and insulation are in direct contact, heat can pass by conduction even if radiant energy is blocked. Attaching the insulation to the inner rafters creates an air pocket between the roof and the reflective surface for much better results.
In areas where temperatures are high and sunny conditions are common, radiant insulation can help keep temperatures down and reduce the cost of home cooling. Radiant insulation is not effective for keeping heat in during cold weather. In fact, heat from sunlight will not be able to pass through the roof, and home heating costs might even rise.