What is a U-value?

What is a U-value—and why does it matter?

If you work with buildings, you’ve likely come across the term U-value. But what exactly does it mean?

A U-value measures how well a building element—like a door, wall, or window—prevents heat from passing through it. In short, it tells you how effective something is at insulating. The lower the U-value, the better the insulation, and the less energy lost.

U-value vs. K-value: what's the difference?

A K-value measures how well a single material conducts heat. A U-value, on the other hand, looks at an entire structure—layers of material, air gaps, and how it’s built. That makes U-values much more practical when assessing how real-world building components perform.

How is a U-value measured?

U-values are expressed in W/m²K—Watts per square meter Kelvin. This tells you how much heat passes through one square meter of a material when the temperature difference across it is one degree.

For example:

• A U-value of 1.0 W/m²K is considered good.
• Lower than 1.0? Even better.
• Higher than 2.0? That means more heat loss.
  

A large insulated sectional door might have a U-value around 1.0 W/m²K—strong performance for applications that require climate control.

The formula behind the number

If you're curious, here’s a simplified formula used to calculate U-values:

Qw = (Ta – Tb) × A / Rw

Where:

• Qw is the U-value
• Ta and Tb are the indoor and outdoor temperatures
• A is the surface area in square meters
• Rw is the thermal resistance of the material or assembly

Most of the time, you won’t need to do this calculation yourself—U-values are provided in product specifications.

U-values and energy regulations

Energy efficiency standards are evolving fast, especially in Europe. Since 2021, the "nearly zero-energy building" (nZEB) requirements have made thermal performance a priority for all new buildings.

The 2024 update to the Energy Performance of Buildings Directive (EPBD) goes even further. By 2026, EU countries must enforce minimum thermal performance levels for elements like external doors and windows.

Typical targets include:

• 1.4 W/m²K or lower for industrial and commercial doors
• 1.2 W/m²K or lower for high-performance residential doors
  

These values may vary by region, but the direction is clear: tighter insulation is becoming the norm.

Why it all adds up

Good U-values don’t just help meet regulations—they reduce energy use, lower heating and cooling costs, and support long-term sustainability. Whether you're designing a new building or upgrading existing ones, understanding U-values is key to making smarter choices for performance and comfort.

Looking for doors with strong thermal performance? Explore our range of energy-efficient automatic entrance and industrial doors here.