What is C-Value in roofing insulation?
This post is part of four-part series exploring energy efficiency values in insulation, such as K-Value, C-Value, R-Value, and U-Value.
What’s C-Value? Is C-Value the same as K-Value, R-Value, or U-Value?
We know that insulation is designed to inhibit environment influence due to weather and other external forces, but how do we know which insulation type is better or worse than the next? Insulation types are rated against a variety of energy efficiency values, such as K-Value, R-Value, C-Value, and U-Value. Today we’re exploring the C-Value energy efficiency rating and how it relates to the quality of a particular insulation type.
What’s C-Value?
The “C” in C-Value stands for “Conductance”. This is a specific instance in which the density of an insulation material dictates its C-Value. ASTM International defines C-Value as the following:
“Conductance, thermal, n: the time rate of steady state heat flow through a unit area of a material or construction induced by a unit temperature difference between the body surfaces.” (ASTM International C168)
The definition of C-Value is very similar to K-Value with one important distinction: the thickness of the material in question. Let’s remove the confusing part of C-Value by simply stating that the thicker the insulation, the lower the C-Value, the more energy efficient the material. Thicker insulation = better insulation.
So, are C-Value and K-Value the same concept?
Not quite. K-Value measures the thermal conductivity across a surface area in response to energy flowing directly into an insulation. (Thermaxx) If you picture a fan blowing cold air directly onto a 2 ft. x 2 ft. piece of insulation, that measures the K-Value. The C-Value determines that the same 2 ft. x 2 ft. area will be have a different environment if the insulation is 1″ thick compared to 6″ thick. Obviously, the thicker insulation will be able to slow down, if not altogether stop, the cold air being blown by the fan.
No matter how high you turn up the fan or how cold you continue to cool the air, it doesn’t change the C-Value because the thickness of the two materials stay the same. If you shrink the 6″-thick insulation down to 4″ thick, you reduce the C-Value by 33% (6″-2″ = 4″ or 67% of 6″).
Again, the math may seem complicated until you see how energy affects different insulation types. Our R&A Contracting team works with commercial roofing clients across the St. Louis area to show you how much an energy value, like C-Value, can change your energy bills in just a few months. If you have questions about choosing the right energy-efficient roofing material for your warehouse or office space, we’re St. Louis’ best at keeping you and your team comfortable, no matter what season it is.