Radiant Barrier or R-value? What if you can only choose one?

When people ask us which one is better, radiant barrier or traditional insulation, the truth is, it’s hard to answer without some more information. Radiant barrier and traditional insulation both play a part in an energy efficient and comfortable living space, but they work in different ways. We advocate for using both in most cases, but what happens when you can only choose one (either for space restrictions, budget restrictions, etc.)? Then which one is the best? Read on.

Conductive Heat vs. Radiant Heat

A quick recap on the two types of heat a home, or structure, has is imperative before we begin. Conductive heat (also called thermal conduction) is the “movement of heat from one object to another one that has different temperature when they are touching each other. For example, we can warm our hands by touching hot-water bottles.” (Source) Radiant heat is defined as, “heat transmitted by radiation (through the air).” (Source) Radiant heat travels until it’s absorbed or reflected; if it’s absorbed, it converts into conductive heat, if it’s reflected, it continues on as radiant heat until it hits another object.

To further simplify it, conductive heat travels in objects (ie. as they touch one another the heat bridges from one object (the warm one) to the other object (the cooler one)), where as radiant heat travels between objects (in the gap/expanse of air between them). So on a sunny day, the sun’s radiant heat is traveling through the atmosphere, through the air and then it hits the roof of the home where it gets absorbed and becomes conductive heat. It uses conduction to travel down, into the home via the roof until it gets to the attic space (air) where it’s then converted BACK to radiant heat and travels downward through the attic space/air, toward the insulation. When it reaches the insulation, it converts back into conductive heat, and on it goes. Anytime the heat reaches an object, it’s takes on its conductive form, and anytime the heat reaches an air space, it takes on its radiant form. Now you can start to see how heat gain works for homes, warehouses, sheds, barns, or anything that is exposed to heat!

Slow Down Conductive Heat,
Block Radiant Heat

Traditional insulation (fiberglass, spray foam, cellulose, denim, etc.) all work in basically the same way. They absorb radiant heat (which converts into conductive heat) and the heat slows down. Think of these products like a sponge, they absorb heat and slowly release it over time. Depending on the r-value, each product will slow down heat transfer a little or a lot.

Radiant barrier reflects (blocks) radiant heat. Think of it like a reflector – the heat “bounces” off the foil layer and gets diverted away. The foil does not change the amount (intensity) of the heat reflected but it does change the temperature of the things below it, since they’re no longer absorbing that radiant heat.

What’s best in a home?

A house is a livable space that is being heated, cooled, or both. This type of space is mostly climate controlled and because people live in it, this is a year-round effort. Every home is built with some type of r-value to slow down conductive heat. By installing a radiant barrier between the traditional insulation and the roof, the radiant heat that would normally be absorbed by the attic insulation is now reflected/directed away.  So in a home, the best option is to combine radiant barrier with traditional insulation to get the most comfortable home.

A great way to picture this, is to think of your home as if it’s a giant refrigerator – except you are keeping it at about 75 degrees. Basically, you want a well-insulated box (accomplished by using regular insulation) and you would also want to put it in the shade (effect accomplished by using radiant barrier). Radiant barrier is your first line of defense against radiant heat, and traditional insulation is you second line of defense against conductive heat.  You really need both – especially in hot climates.  

Bottom line: You should use both a radiant barrier & regular insulation in a home/residential attic space.

What’s best in my workshop?

In a non-conditioned space like a shop, a barn, a shed, etc. the goal isn’t to climate control the space to make it comfortable 24/7, because you’re not living in it! Even though you may occasionally heat the space or run an a/c in the heat of summer, the main goal is to make these spaces comfortable on their own, without the constant need for heat or a/c. Ask yourself this question, would you rather block heat transfer or just slow it down? A radiant barrier is best for non-conditioned spaces because it will act like a tree (mimicking shade) over the building.

Bottom line: A radiant barrier out-performs regular insulation in a workshop, barn, warehouse, shed, or any other structure that’s not climate controlled (ie. not a home).

What’s best for a metal building?

A metal building would fall into a similar category as the workshop example above, with the main difference being that metal buildings in colder climates can have problems with moisture/condensation. For an application like this, the foil is still going to make the biggest impact to reduce heat gain in the summer, but adding a small amount of r-value is also worthwhile because this will keep the interior surface temperature of the metal sheathing above dew point (this prevents condensation). This type of application is a perfect use for BlueTex™ Insulation. BlueTex™ blocks 97% of radiant heat on the foil side and stops moisture and condensation problems with its foam-core center.

BlueTex™ insulation was designed for all kinds of metal buildings – pole barns, warehouses, shops, sheds, airplane hangars, storage unit facilities, poultry and livestock facilities, and many more! If you’re in a cold climate and insulating a metal building, you can learn more about this product at: www.BlueTexInsulation.com

Bottom line: A metal building that sweats will benefit most from a radiant barrier combined with a little bit of insulation (r-value), to keep the interior surface above the dew point while still blocking radiant heat transfer (into or out of the building).

Radiant Barrier Foil vs. R-Value Insulation: Final Verdict

As you can see from the example above, this question of which one is better has to do with the specific project but the case can be made that no matter what project you’re doing, if radiant heat is part of the problem, then a radiant barrier is the best thing to use to solve that concern.

Remember, regular insulation is important and radiant barrier doesn’t replace the need for r-value. In homes and living spaces, using both radiant barrier and insulation is useful and effective. For other spaces that don’t require controlled temperatures, a radiant barrier can help mitigate radiant heat gain/loss.

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