Is Paint An Effective Radiant Barrier In The Attic?

Is paint an effective radiant barrier in the attic?  In short, the answer is no.

I had heard, but had not yet seen, that there is a contractor running around telling people that he can get them "energy savings" if they paint their attic spaces his special silver-colored paint, and it will save zillions of $ in energy.

Well, I finally saw such an attic!

Interior Radiant Control Coatings (IRCC) include radiant foils and the so-called "ceramic" paints.  Any such paint must meet standards determined by the American Society of Testing and Materials, which recently changed its name to ASTM International.  And they do just that.  They set standards for many things.

Any such so-called radiant barrier control paint, "ceramic" paint, or whatever, is supposed to meet an ASTM standard stated in ASTM C1321.  The Reflective Insulation Manufacturers Association (RIMA International), has agreed with the definition of that standard, which is a barrier that provides better than 75% thermal reflectivity, and a thermal emittance of 0.25 or less.

Of course, RIMA states that radiant barriers are more effective in warmer climates, and less in mild and cold climates.  But that regards the foils, not paints.

RIMA says (click here for the full statement), "One of the major misconceptions in the insulating paint field is that “ceramic paints” can be used on the interior like an IRCC to reduce attic temperatures and lower cooling energy costs. However, the application of a “ceramic paint” to the underside of roof sheathing may increase the attic temperature because “ceramic paints” typically have a higher emittance than the sheathing deck."

Paint is not a "barrier."  It is a misconception to call it such.  All of the standards people warn about contractors that use inferior paint and claim it meets standards, they water it down

In this attic only about 2/3 of the roof sheathing was so painted.  I could see where they painted over mold, so the coating was very thin.   And they painted the sheathing over only one half of the house!  So this was a complete lie perpetrated onto an unsuspecting, but trusting, homeowner.

Here is the dirty little secret.  Not that much radiant heat actually influences the interior of the house.  And nobody seems to be able to determine energy savings when such radiant barriers are installed!  That is what insulation is for!  And in a consumer report states that foil studies show that any insulation that provides R-39 or better will be more effective in the long run than any radiant barrier (foil or paint) that can be added to an attic space. 

So, there it is.   We are better if we insulate better!  Insulation in an existing house can always be added to, and when that is done the insulation value is cumulative.

My recommendation:  before you go to the expense of "improving" the energy efficiency of your home, investigate it completely.  Research is easy these days.  Find out what you can find out.  But trusting the claims of contractors who want your money is not the best way to go.  It probably never is.