Heat Transfer & Thermal Values

Understanding thermal values of insulation is the foundation of every smart insulation decision. Whether you’re building new or upgrading an existing structure, these numbers tell you how well your insulation is actually working and how much money is quietly leaving your building every day it isn’t. Here’s what each value really means.

R-Value: Thermal Resistance

Insulation R-value is the measure of a material’s ability to resist heat flow. The higher the R-value, the greater the thermal efficiency and the less energy your HVAC system needs to maintain a comfortable interior temperature. When people talk about the R-value in insulation, the meaning is: it’s a number that tells you how hard your insulation is working to keep heat in or out.

For metal buildings specifically, metal building insulation R-value requirements vary by climate zone and building use, but most commercial applications call for a minimum of R-19 in walls and R-30 or higher in roofs. Here’s a general insulation R-value chart for common metal building insulation thicknesses:

Keep in mind that compression at purlins and girts reduces the effective performance of the R-value of insulation in metal building performance, which is why system design and proper installation matter just as much as the product itself. You can read more about this on our Metal Building Insulation page. 

U-Value: Overall Heat Transmission Coefficient

The U-value is a sum of each of the parts of a roof or wall system and how well it reduces energy loss. U-value is a calculation that takes into account all of the factors of wall or roof construction which includes the way the insulation is installed, the type of exterior panels, screws, girts/purlins, etc. of insulation is a unit used to express heat passage through a complete building section, including air films. U-values serve as a basis for determining transmitted heat loss. The lower the U-value, the higher the insulation value.

How R-Value vs. U-Value Differ 

R-value measures a single material’s resistance to heat flow, while U-value measures the thermal performance of the entire building assembly, walls, roof, framing, air films and all. 

In practice, the U-factor in metal building is the number most relevant to energy code compliance, as it reflects real-world performance across the full envelope rather than just the insulation layer in isolation. 

If you’re wondering why your building’s real-world performance doesn’t match the numbers on paper, the short answer is thermal bridging. Steel purlins and girts conduct heat directly through the envelope regardless of what’s between them. A quick answer to this can be found below in the frequently asked questions section.

F: Surface Air Film Coefficient

The amount of heat flow in BTU per square foot per hour between an exposed surface of a material and the adjacent air. It is the measure of the conductance of heat through the air film that clings to all surfaces. Air films on both the interior and exterior surfaces of a wall or roof contribute a small but real resistance value to the overall thermal assembly.

Frequently Asked Questions

What is a good R-value for a metal building?

For most commercial metal buildings, a minimum of R-19 in walls and R-30 in the roof is the baseline for energy code compliance in moderate climates. In colder climates or for conditioned spaces with significant heating and cooling loads, R-38 or higher in the roof is often recommended. The right R-value of insulation in metal buildings depends on your climate zone, building use and local energy codes. Our team can help you identify the right specification for your project.

Why does my metal building underperform its rated R-value?

Several factors reduce the real-world R-value of metal building insulation below its nominal rating. The most significant is compression. When insulation is compressed at purlins and girts, its effective R-value drops substantially. Thermal bridging through the steel frame itself also bypasses the insulation entirely, transferring heat directly through the structural members. 

This is why calculated thermal values of insulation often look better on paper than in practice and why choosing a system engineered specifically for metal building construction matters. 

Do metal buildings need a higher R-value than wood-frame buildings?

In practice, yes, though the code-required numbers may be similar. Steel conducts heat roughly 300-400 times faster than wood, meaning the structural frame itself creates continuous thermal bridges that wood framing does not. Achieving equivalent real-world performance in a metal building requires a system designed to minimize that bridging effect, not just meet a nominal insulation R-value on the product spec sheet.