If you’re looking at insulated garage doors, you’ve probably come across U-values in the specifications. You’ll see numbers such as 0.5 W/m²K, 1.0 W/m²K or 1.4 W/m²K, but what do they actually tell you?
The basic rule is fairly simple:
Lower U-value = slower heat transfer = better thermal efficiency.
Higher U-value = faster heat transfer = poorer thermal efficiency.
Where garage doors get slightly more complicated is what that U-value is actually measuring.
A manufacturer may quote the U-value of an individual insulated panel or section, while another figure may refer to the complete fitted garage door. Those numbers aren’t directly comparable.
Here’s what you need to know when comparing garage door insulation.
What Is a Garage Door U-Value?
A U-value measures how quickly heat passes through a material or product. It’s expressed in W/m²K (watts per square metre kelvin).
The smaller the number, the more resistant the product is to heat transfer.
So, if you’re comparing two equivalent complete garage doors:
- 1.0 W/m²K offers better thermal performance than 1.4 W/m²K
- 1.4 W/m²K offers better thermal performance than 2.0 W/m²K
But the important word here is equivalent.
Before comparing two figures, you need to know whether you’re looking at the U-value of an individual garage door panel or the U-value of the complete door.
Panel U-Value vs Complete Garage Door U-Value
This is one of the most important things to understand when comparing insulated garage doors.
An insulated sectional garage door isn’t simply one large insulated panel. The complete door includes the individual sections, joints, seals, frame and other components needed for the door to open and close.
All of these affect its overall thermal performance.
That’s why the U-value of an individual insulated section is normally lower than the U-value of the complete garage door.
Hörmann LPU 42 Example
The Hörmann LPU 42 sectional garage door is a good example.
It uses 42mm double-skinned insulated sections.
The section itself has a U-value of approximately 0.5 W/m²K, whereas the complete fitted garage door has a U-value of approximately 1.4 W/m²K.
With the optional Hörmann ThermoFrame, which provides a thermal break between the frame and the brickwork, the complete-door figure can improve to approximately 1.2 W/m²K.
So, if you saw 0.5 W/m²K quoted for an LPU 42, it would be incorrect to assume that’s the U-value of the entire garage door.
What Difference Does a Thicker Garage Door Panel Make?
Panel thickness can make a difference to thermal performance, particularly when comparing doors with similar construction.
We can see this by comparing two Hörmann sectional garage doors.
| Garage Door | Section Thickness | Section U-Value | Complete Door U-Value |
|---|---|---|---|
| Hörmann LPU 42 | 42mm | approx. 0.5 W/m²K | approx. 1.4 W/m²K |
| Hörmann LPU 42 + ThermoFrame | 42mm | approx. 0.5 W/m²K | approx. 1.2 W/m²K |
| Hörmann LPU 67 Thermo | 67mm | approx. 0.33 W/m²K | approx. 1.0 W/m²K* |
*The complete-door figure for the Hörmann LPU 67 Thermo is based on a 5000 × 2125mm door.
The LPU 67 Thermo uses thicker 67mm insulated sections and achieves a section U-value of approximately 0.33 W/m²K, compared with approximately 0.5 W/m²K for the 42mm LPU 42 section.
Remember our basic rule: the smaller the U-value, the slower the heat transfer and the better the thermal efficiency.
But the table also shows why you shouldn’t compare panel figures alone. For a more realistic indication of the finished garage door’s thermal performance, look at the complete-door U-value.
What About Other Makes of Sectional Garage Doors?
The same principle applies to sectional garage doors from other manufacturers.
They also offer insulated sectional garage doors with different panel constructions and thermal specifications. As with Hörmann, the U-value of the insulated panel itself can be lower than the U-value achieved by the complete garage door.
The final figure can also vary depending on the size and specification of the door.
This is why, if you’re comparing different manufacturers or models, it’s important to check whether the figures you’re looking at refer to:
The insulated panel or section
or
The complete garage door
Otherwise, you aren’t comparing like-for-like.
Why Does the Garage Opening Matter?
Even the U-value of the garage door doesn’t tell you everything about how your garage will perform.
The condition of the garage opening matters too.
Uneven floors, gaps and the condition of the surrounding opening can all affect how effectively a garage door seals.
It’s also important to remember that a garage door isn’t the same as a solid external wall or front door. It needs joints, seals and moving components so that it can open and close.
An insulated garage door can reduce heat transfer, but it won’t make the garage completely airtight.
That’s one of the reasons we carry out a free home survey before ordering your new garage door. We can properly measure and assess the opening and discuss which options are suitable for your property.
So, What Is a Good U-Value for a Garage Door?
There’s no single number that’s right for every garage. Instead of simply looking for the lowest number you can find, start by asking:
What is this U-value measuring?
If it’s a panel U-value, don’t compare it directly with another manufacturer’s complete-door U-value.
Then consider how important insulation is for your particular garage.
For someone with an integral garage beneath a bedroom, thermal performance may be a much bigger consideration than it is for someone with a detached garage used purely for storage.
The simplest rule to remember is:
Lower U-value = better thermal efficiency – but only compare like-for-like figures.
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