If I install a radiant barrier under my roof, won’t it overheat the roof and cause damage to it?
The simple answer is no. While it seems logical that the radiant barrier reflecting 97% of the radiant heat back would make the roof would get hotter, it doesn’t exactly work that way.
In all testing that has been conducted, roofs with a radiant barrier properly installed (the foil MUST have an air gap on at least one side) have only shown to increase temperatures by just a few degrees (usually between 2º and 10º degrees Fahrenheit), if at all. This number is so low that it is considered trivial and so the radiant barrier under the roof does not cause any issues/problems with raising roof temps. Keep in mind that typical roofing systems and buildings are designed to handle temperatures well above what they actually reach. Many roofing manufacturers recommend using radiant barriers and some areas even require it.
What Determines Roof Temperature?
There are two things that determine how hot a roof will get: the amount of ventilation around the roof and the color of the roof. Air movement (ventilation) and air temperature around all sides of the roof will affect the overall roof temperature. The roof absorbs radiant heat from the sun, and air flow (wind/ ventilation) has a cooling effect on the surfaces of the roof, helping to bring down the overall temperature. This is important because the cooler a roof is overall, the less radiant heat it emits. That means that if your roof was only as hot as the outside air temperature, then you technically wouldn’t need radiant barrier at all! On top of that, the color of the roof color also contributes to how hot a roof can get; dark colored roofs can easily get 20ºF+ hotter than light colored roofs on a sunny day.
With these two factors at play, every roof will eventually reach a point where the maximum temperature stabilizes. This happens when heat absorbed from the sun equals the heat being lost due radiation, ventilation and air temperature.
Where Does the Reflected Heat Go?
Without a radiant barrier, all of the heat coming off underside of the roof is reflected or absorbed into the building and the items in the building (insulation, equipment, people, etc.). When you add WareHouseFoil™ to the roof line (at any point above the insulation or ceiling), the heat is bounced back toward the roof, causing the roof to reabsorb the heat and then emit more heat upward, rather than both upward and downward. The roof still is gaining and loosing heat; the radiant barrier is basically just directing the (same amount of) heat away from the building and its contents.
A simpler way to understand this better is to consider a room with one light source (in the form of an unshaded light bulb) hanging in the middle of the room. Under normal circumstances, the bulb sends out light (and heat) in all directions, illuminating the room. Now, if you add a reflector/shade to the bulb, the light (and most of the heat) is directed downward, below the reflector. The amount of light (and heat) the bulb produces has not changed; what has changed is the direction the light and heat are going. This is the same concept that happens with a radiant barrier under a roof. The amount of heat on a roof hasn’t changed (by much), it’s just that now instead of heat radiating in all directions (upward and downward from the roof) it’s mostly being radiated (forced by the reflective radiant barrier) upward and away from the warehouse or building.