One common question or concern about installing a radiant barrier is whether it will cause the shingles to heat up and get damaged or shorten their life expectancy.
The short answer is NO damage will occur. Tests have shown that installing a radiant barrier in attics generally only cause the roof and shingles to increase about 2° – 5° Fahrenheit.
This may seem unbelievable since radiant barriers are sold on the fact that they will reflect 97% of radiant energy away from their surface. The question is asked “Where Does The Heat Go?” It is assumed that since the heat is reflected back towards the roof then the roof must experience a significant increase in temperature.
Let me explain exactly what is happening between the sun, the roof (shingles & decking material), and the attic.
First, radiant energy from the sun heats up the shingles. The actual temperature of the shingles is primarily determined by two things: 1) Shingle color – darker shingles absorb more heat and get hotter, and 2) outside air temperature. Obviously, your roof will get hotter on a hot-sunny day compared to a cold-sunny day.
Once the heat is absorbed by the shingles, it is transferred via conductive heat flow to the roof deck. The roof then becomes a “sponge” to hold the heat. On the other hand, air has a cooling effect. How much is determined by the actual outside air temperature and the amount of airflow on the roof either by wind above the roof or attic ventilation below the roof.
These factors: Amount or Angle of the Sun, Shingle Color, Outside Air Temperature, and Airflow will determine the “Maximum Roof Temperature”. At this point, the roof will not get any hotter. Your geographic location will also affect this. A roof in Las Vegas will get hotter than a roof in Kansas. In general, maximum roof temperatures will range from 130° up to 180°.
I mentioned that the roof becomes a heat “sponge”. As the temperature goes up it will want to release the heat by converting it to radiant energy. This radiant energy is emitted in all directions, both upward to the sky and downward into the attic.
By installing a radiant barrier, the energy heading towards the home will be reflected back up towards the roof and cause MORE heat to be sent towards the sky away from the home. This is similar to a light bulb with a reflector behind it. The amount of heat and light given off by the bulb is constant, but you would feel less heat behind the reflector and the light is directed to one side.
Shingle manufacturers also provide a full warranty on products installed over radiant barriers. Your geographic location and color of shingles are the two biggest factors in determining roof temperatures.
The bottom line is that shingles usually see a SMALL increase in temperature (usually 2°-5°) over radiant barriers. These results are from tests performed by the Department Of Energy. Plus, many tests performed by customers and installers support this fact. This slight increase in roof temperature is considered nominal and will have virtually no impact on the performance or life expectancy of your roof. Rest assured, Your shingles will NOT BAKE.
Tags: Attic Insulation, conductive heat, radiant barrier, roof shingles
Thanks for reference to your article. Very helpful! Don
If the attic foil is installed on top of the attic insulation,
is the space between the attic foil and the roof hotter because
of the reflected heat in comparison to the same space without
the presence of an attic foil layer.
Our current house has the standard ridge venting .
Would the implementation of attic foil necessitate additional
venting ?
Klaus,
It’s tough to say exactly. Heat that would be absorbed by the insulation is being reflected back towards the roof. However, very little radiant heat is absorbed by air. Radiant heat goes right through transparent objects like glass, air etc. So, from testing different roofs over a radiant barrier they tend to increase only a few degrees in temperature.
In theory, this COULD cause the actual air inside the attic to go up a few degrees depending on the ventilation.
I’m always in favor of good ventilation ESPECIALLY if there is ductwork in the attic. Here is an article on proper attic ventilation: