I have seen mold growing under a radiant barrier installed over blown in insulation.  I am looking for any articles, etc.... about this problem to forward to a customer.  Can anyone help?

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Hi Tom.  I understand the concern.  Unfortunately, there have been many products out there that have given our industry a black eye over the years.


Here is an example of how we perform on school modular units in cold climates. 

This is in Texas where it can reach 0 degrees and -12 with the wind chill.


















































































Hello Rob, I've researched this to some extent, and have worked with DOE on issues relating to offgassing when foam is applied next to a radiant barrier. So as I get this straight; Are you saying blown in on radinat heat in flooring, with say pex stapled up under the flooring and then applying blown in foam, or any radiant barrier in walls or roofiing?

I will look through my emails and articles about this as well.




Robert Haverlock

CSBA and IAQ for Healthy Buildings  


I am looking for a study or article or whatever done by an independent source on applying the foil type radiant barrier applied over blown in attic insulation.  One attic i've seen this done in caused moisture to build up on the underside where it contacted the insulation and mold formed.  A potential energy audit customer had this radiant barrier added in their attic and I explained the potential problems.  I would like to give them some independent study/article confirmation of this but cannot find anything.  I know what and why this happened.  but I'd like to give them something from someone besides me.   I am located in central PA where the summers are humid and we can have rather cold winters.  The homes that are being retrofitted with insulaton are built before the air sealing techniques done today were in practice so they are very leaky allowing the moist warm air to escape in the winter months.



Here are a few studies I have on our company servers. It has been very difficault for me to find studies pertaining both to an RB on top of insulation and mold development as a result. I would suspect that you could find studies or papers on just mold growth and the conditions needed to develop it and then show your customer how placing the RB on top of the insulation could result in mold growth.


My company has installed thousands of radiant barriers and never one laid on top of insulation for this reason and a few others. I have had customers pay us quite a bit to remove foil laid on top of insulation and have had to stop mid-job due to what appeared to be mold growth. After consulting a removal company, they reported the circumstances as very normal for their business.


I've uploaded the last study, it is over the size limit for this site. The study titled "Thermal and Moisture Performance of RBS" is very technical but touches on the moisture subject on page 10. I had to pay for this study about three years ago if I remember right but it is very technical. You might be able to highlight just the relevant material and send to the customer.

Link to "Thermal and Moisture Performance of RBS":



Hope this helps!



Your Fact Sheet states:  

"These estimates generally assume R-19 ceiling insulation. Savings would be less for homes with greater levels of insulation."

R-19 is an inadequate amount of insulation in most climates - surely the mid-Atlantic where I work. Correct me if I am wrong, but everything I have read points to added insulation being a cheaper way to save the same amount of money as a radiant barrier if you have low insulation in a mixed climate.

Ed Minch

Hello Ed,

R-19 is pretty low. I have about 70 research papers on Radiant Barriers, most of which from credible sources and research organizations. Most of the papers conclude with many different opinions.

The general consensus is that RB's are not the solution for every home or situation and should almost never be installed without adding more insulation or ventilation. (three types of heat transfer, three different parts of a good system)

In my part of town, the Dallas, TX metroplex, RB's are great for a lot of the homes as we typically have all of our duct work and HVAC equipment in the attic. Still, we only install RB's in about 50% of the homes we do work in. A lot of time, we only recommend adding insulation.

You can imagine a 3500 sq. ft. one-story home with a 12/12 roof pitch would be very expensive to install a RB so probably not the best use of the homeowners budget. On the other side of the range, a two story home with a small attic and all the duct work and HVAC equipment in the attic can have a RB installed for very little cost where just adding insulation would not make a large impact on the duct work or air handlers in the attic (even improving the attic ventilation would not make a significant impact on it's own).

I'm not sure about the extent of your research into the matter or the amount of time you've dedicated to learning about RB's but everything I have read points in different directions depending on a multitude of conditions.One study a lot of companies down here use is from about 20 years ago and states that foil placed on the attic insulation is by far the most effective application AND dust does not have an effect on it!

We have had many many happy customers, only a few un-happy customers, and some that didn't respond to our questionnaires. Generally, I think if your an educated, well informed, honest contractor, you should be able to accurately determine what is in your customers best interest before doing any work and only recommend a radiant barrier when it will be worth the money. 


Unfortunately, there are many contractors in my part of the world selling radiant barriers for $10k or more and promising customers to cut their bills in half with just a RB! That kind of behavior gives us all a bad rap and undermines those of us with a good conscious.


Hope that better explains my position on the matter.


I think we are in basic agreement.  If you want to cut your bill, you have to cool off your interior drywall ceiling (in summer) so you don't spend so much money air conditioning it.  If you put up a radiant barrier, it will cool the ceiling by cooling the attic.  If you insulate, it will cool the ceiling by slowing down the heat flow from the hot attic.  Do whatever is cheapest. And ducts throw a monkey wrench into the whole thing.

Many of the studies I have read use that same R-19 starting point as the one you cited.  If this is the case, then the cheapest way to a cool ceiling in summer is through insulation - cheaper and more effective here in the mid-Atlantic.

Ed Minch

That's the simplest explanation. I like the term of cheapest way to a cool ceiling. 

Keep in mind, studies have also shown that a large portion of infrared heat radiates through most types of insulation since they are usually very porous and light.

That could mean that even with a deep amount of insulation, a good amount of radiant heat gain is still taking place without a radiant barrier. Some people have contributed the effect of feeling hot in your home, even though the thermostat says 78 just like it does in the spring, and you don't feel hot then.

Without more research on this particular effect, it's hard to tell if those that claim this are just full of hot air or actually speaking truth. I guess the question there is whether or not someone feeling hot in their home in the summertime even the the thermostat is reading the same temp as in the spring, is a psychological issue or a real world phenomenon of radiant heat gain.


The physics, as I understand it, say that a small portion of the long infrared band of energy pass through most objects until it reaches a very dense material such as human beings, granite, water, or other very dense material. More research is needed on this effect in homes and whether or not it truly affects human comfort factors. 


This would be easy to test.  Install 1/2 of an RB in an attic, then measure the drywall temperature on each side.  The cooler drywall wins.  Come to think of it, install more insulation in 1/2 and an RB in the other 1/2.

Ed Minch



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