Radiant barriers are effective in reducing cooling bills in areas that are hot by blocking some of the heat that your roof absorbs from the sun in summer. The hotter the weather or climate, the more effective a radiant barrier is. Some say they are not effective in cold weather, but others contend they can be used to reflect heat back inside a house that would otherwise escape through the roof. Still, radiant barriers are most effective in high temperature areas.
A radiant barrier is a reflective insulation system, which blocks heat as opposed to absorbing it, which is what traditional insulation does. When the heat of the sun beats down on a roof, it heats the surface and that heat has to go somewhere. Some of the heat is conducted through the structure itself. Once inside the house the hotter air rises and the cooler air sinks. Eventually the heat in the attic will move down into the rest of the building through radiation. A radiation barrier stops the heat from going down into the house by reflecting it back to where it came from.
By blocking the heat, the barrier reduces the overall cooling bill in summer. The barrier is made of aluminum, and connected to another surface for installation. The aluminum reflects the heat back in the direction it came from, away from the house. The aluminum surface must face an open-air space to be effective.
Anything touching the aluminum surface can reduce its effectiveness as whatever is touching it will conduct the heat to the rest of the building. Dust can also reduce its effectiveness over time.
The amount of savings that can be realized depends on a lot of factors. The radiant barrier is more effective the hotter it gets, so it would do more in 110-degree heat than 85-degree heat, for example. The energy.gov website says the radiant heat barriers can reduce cooling costs by five to 10 percent in a hot climate. Manufacturers of these products claim up to 15 percent savings.
It works by reducing the amount of heat that comes from the attic by 20 to 40 percent. This means the cooling unit does not have to work as hard to cool the house or building. It could allow a house or building to use a smaller air conditioning unit as a result, and that would be added savings.
The radiant barrier does reflect heat back toward the roof. A shingled house would have shingles that would be even hotter than normal in summer as a result of having heat thrown back at it. It is estimated the heat of shingles goes up five to 10 degrees as a result, but there is no indication that the shingles are harmed as a result.
Radiant barriers are effective, but they are not a single answer that will solve every issue. Radiant barriers should just be part of insulating a home to save energy through the summer.