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° – 10° 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.
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:
I saw your reply to a YouTube video. I had also wondered how a radiant barrier would effect the roof. Your explanation makes perfect sense. Thanks for the excellent information.
Due to a recent hail storm I’m going to have a new roof put on my house. I’m considering using sheet radiant barrier instead of 30 lb. felt, placed on the decking, then 30 yr. asphalt shingles. What’s your recommendations on a good sheet radiant barrier product to use, and the benefits of using it rather than roofing felt.
Thanks,
Eldon
I would discourage using radiant barrier as your primary waterproofing layer. Felt products are relatively cheap and provide excellent “waterproofing” ability yet still allow moisture to pass through or the ability for the wood deck to “dry out”. Secondly, you CANNOT apply shingles directly on top of a radiant barrier product and still have a radiant barrier. Radiant heat by definition is heat transfer ACROSS an airspace. Without an airspace, you cannot have radiant heat much less a radiant barrier. Here is blog post and video on Why Is An Airspace Required For a Radiant Barrier To Work
If you can incorporate an airspace into the roofing assembly, you can put AtticFoil Brand Radiant Barrier Foil directly over the felt under the roof. Here is information on How To Install Radiant Barrier In Roofing Systems.
You said “you can put AtticFoil directly over the felt under the roof”. What does this mean? Over the felt is on the outside, under the roof is on the inside.
Greg, with a tile roof there is space between the tiles and the roof deck. The tiles are the “roof”. So, you can put the AtticFoil Radiant Barrier foil BETWEEN the tiles and the roofing felt.
What about baking the roof decking? I’m concerned reflecting the radiant heat back through the roof will cause dry rot to the roof decking. Have you conducted any tests on the decking?
David,
This should not be a big deal. While I haven’t done testing to see the results, I do plan to test this out to see what conclusions can be made.
Yeah I was looking for more ways to save money on electricity and recently I went up into my attic. It was 160F here in Texas. I am now researching these radiant barriers and was wondering about the shingles & roof damage. After reading this I feel more confident. Thanks.
Quite a few great issues on this site and truly just didn’t have a clue concerning almost any of this in the past so with thanks for your knowledge
Great information, thanks for the education. Just one question, I have a contractor that wants to just lay the foil barrier on top of my insulation. What do you think would work best, stapling to rafters or just laying foil on top of insulation. It seems like stapling to the rafters would be more effective in reducing overall heat in the attic and lead to lower house temperatures in summer. But placing the barrier over the insulation may help keep the house warmer in the winter. Or should I just do two layers, one stapled to the rafters and one laying over the insulation, or is that overkill and a waste of money. Thanks for sharing your knowledge.
To determine which method is better for your home, it depends on what you have in the attic space. I recommend you read this article on the AtticFoil website: Choosing the Best Install Method
Additionally, we have many customers who have the time and energy to do both methods and see good results. Though it is not essential to do both in order to see a vast improvement, doing both methods will yield the best possible results year round if you have items in the attic. Read the article, consider your situation and then decide.