Radiant barrier over blown in insulation — Home Energy Pros

Radiant barrier over blown in insulation - Home Energy Pros

Radiant barrier over blown in insulation

Replies to This Discussion

Hi Rob,

We need more information, the type of insulation, the climate, is there heat and ac, is there a vapor barrier, and what air sealing measures have been taken?

Umm, the required 1″ space is correct, but by the way you worded it is off & the placement depends on ones climate. In the south it should be under the sheathing or rafters to reflect heat back out of the attic. Up north due to venting, ice-dams, etc. if one is crazy enough to use it, it should be on top of the insulation to help reflect it back down.

+1 on that. The RB material is performing as a condensing surface instead. What a perfect way to demonstrate attic leakage.

Considering that most of us live in areas that have heating and cooling seasons, a radiant barrier that doesn’t work in both ways is counterproductive for at least part of the year.  Some might argue that for many, it is counterproductive for most of the year.  It would be nice to be able to move it around or even remove it under certain conditions, but that isn’t an option, so the challenge is to find the best location for the average conditions throughout the year in a specific location.

If you are are going to have it in contact with the insulation, it should be on the proper side of the insulation to do much good.  That would be the warm side of the insulation, not the top, and it requires a minimum of 1′ air space above the ceiling plane, which isn’t very easy to achieve for most installers.  Laying a radient barrier on top of insulation in an attic seems like a very poor choice to me in any climate.  If the point is to stay warmer, I’d say you’ll be hard pressed to see much difference.    Also, placing it on top of the insulation guarantees that the top surface will no longer reflect in a matter of years because it will be covered with dust.

Placing it under the rafters, as I suggest, means that radiant heat has a harder time making it to the insulation in the summer, and if you have a good ridge vent and soffit vents, you can get good convection currents between the rafters to get the heat out of the structure, and it will take much longer for dust to build up.  Placing it in contact with the roof deck often doesn’t permit the proper air space for the product to perform properly.

Conclusion: Radiant barriers can work well to reduce the cooling load, but are problematic if you are trying to use them to keep heat in the house.

If the radiant barrier in an attic does not «Maintain an intimate bond» with the structure, then it is not going to do much at all.

If it is placed on or above blown in or rolled insulation, or it is installed on the rafters, air will get around, above or below it.  That air always has humidity.  In the process of radiant heat transfer, that humidity goes along for the ride.  The radiant heat enters the walls, roof but the humidty stops there.  Wet walls, roof.

The radiant barrier, if it is worth anything at all, is supposed to stop that radiant heat transfer and prevent the humidy from gathering on the walls, roof or radiant barrier material.

If a radiant barrier material is placed over the insulation on the attic floor and the insulation is getting wet, your radiant barrier material is a joke!

Hi Tom.

For starters, this product is only sold to exclusive distributors.  They are only permitted to sell the coating to factory trained and certified applicators.  If you sent me a chck for 100-gallons, I would have to send it back, I could not sell it to you.

There is a big difference in radiant barriers and radiant barrier coatings.  Someone mentioned suspending the radiant barrier (aluminum foil?) an inch above the blown in insulation.  Whether it is one inch or two feet above the attic floor, how much good is that going to accomplish?  In the hot months the roof is heated by the sun, conductive heat transfer to the under decking.  The underdecking then transfers that heat energy by radiation and also some by convection as the air in the attic also absorbs that heat energy.

The ‘Aluminum foil’ allows air to travel below and above it.  It gets warmed by the heated air and radiates the heat energy below it into the insulation.  The insulation slows that process down but does not stop it, it still absorbs the heat energy and it is transferred through the ceiling into the living space.  If that radiant barrier still allows the attic to receive any heat anergy, what good is it actually doing?  Heat building in the attic is still transferring into the living area.

Please understand I cannot speak for other coating products, only the one I work with.  I think the way our coating functions is what is confusing to many / most people.

With the ‘aluminum foil’, the coolest that material can possibly be is whatever the ambient air temperature is at that level in the attic at that time.  THE HEAT ENERGY HAS ALREADY ENTERED THE ATTIC AND CAUSED THE HEAT BUILDUP.  The aluninum foil does not stop the buildup from happening or stop it from transferring to the living space below.

With our coating applied to the roof underdecking, that heat energy does not enter the attic.  The heat energy is not allowed to radiate out past the coating’s surface..  This is how an effective ‘Radiant Barrier’ material.is supposed to work but they do not in most cases .  I think this is where the confusion lies.  People only seem to associate the term ‘Radiant Barrier’ as something that ONLY is effective against the sun’s solar load.

You can coat the exterior of the roof, it will reflect and emit the heat away in the hot months AND retain heat in the cold months.

You can coat the plywood on the roof  and then install the shingles, it will still do the same thing acting as a conductive heat barrier.

You can apply it to the attic underdecking.  OR, you can apply it to the floor of the attic prior to installing the insulation. 

OR, you can paint the ceiling of the home and get the exact same results.  IT IS A THERMAL BARRIER, not just a radiant barrier.

As an example;  I supervised the application of our coating to hospital boilers and steam pipes.  The surface temperature of the metals prior, 267 degrees, after 155 degrees, a 35% reduction in heat loss through the metals per the engineer.  This application was performed on graveyard shifts.  At 11 pm one night I got a call from them and went down there.  

 He took a surface temperature measyrement, 155 degrees.  He then asked ne to place the back of my fingers about an inch or so from that 155 degree surface.  I did and he asked what I felt.  I held it there not knowing what I was supposed to feel.  After several second I said I did not feel anything.   He then said «That’s what I’m saying here, we should feel the heat radiating out and it isnt happening.  How do I explain this to Big Mike?».  I said I didnt know.  This was the first time, of many over the years, that someone told me «This is some really weird sh. you got here.» .  I have been told that MANY times over the years.

Just one more thing to add to that «Weird sh,,» folder:  If you paint a wall or coat a roof with our coating and give it a week to cure, then hit it with an infra-red gun (thermometer)  you will not get a reading.  Now do your research and try to explain that one.

We have proven to break the laws of physics many times.


Leave a Reply