Understanding U Values for Industrial Doors & Roller Shutters
Why U Values Cause So Much Confusion
Few subjects within industrial doors create more confusion than U values.
Part of the problem is that the term “U value” is often used incorrectly or without enough explanation. In many cases, information found online compares completely different things without making that clear to the reader.
For example:
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one manufacturer may quote the thermal performance of the insulated lath itself
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another may quote the calculated U value of the complete installed shutter
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another may simply quote a theoretical insulation figure with no explanation at all
These are not the same thing. As a result, customers can easily end up comparing figures that are measured differently and therefore cannot be directly compared. Understanding the difference between these values is important when assessing the true thermal performance of an industrial shutter or high speed door system.
What Is a U Value?
A U value measures how much heat passes through a material or structure.
It is effectively a measure of heat transfer.
The lower the U value:
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the better the insulation
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the lower the heat loss
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the better the thermal efficiency
U values are measured in:
W/m²K
(Watts per square metre per degree Kelvin)
This describes how much heat energy passes through one square metre of material for every degree of temperature difference between the two sides.
The Important Difference: Lath U Value vs Installed Door U Value
This is where much of the confusion begins.
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1. The U Value of the Insulated Lath
An insulated roller shutter curtain is made from individual insulated laths.
Manufacturers often test or calculate the thermal resistance of the lath section itself.
For example:
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a foam-filled insulated lath may achieve a quoted thermal resistance of approximately:
R=1.1 m2K/WR = 1.1\ \mathrm{m^2K/W}R=1.1 m2K/W
This refers only to the insulated profile section. It does not represent the performance of the complete installed shutter.
It does not include:
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guide rails
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bottom rail
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shutter box
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air leakage
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installation quality
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gaps around the opening
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thermal bridging
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operational movement
This is similar to quoting the insulation performance of a brick but not the performance of the complete wall
2. The U Value of the Finished Installed Shutter
The actual installed shutter will normally have a significantly different overall U value.
This figure reflects:
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the entire shutter assembly
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the installation method
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surrounding structure
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air leakage
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thermal bridging
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operational tolerances
The installed door U value is therefore usually:
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higher than the lath-only value
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more representative of real-world performance
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more difficult to calculate accurately
This is the figure that ultimately affects building heat loss.
Why Two Similar Doors Can Have Very Different Real-World Performance
Even if two doors use similar insulated laths, the finished thermal performance may vary considerably.
Factors influencing the final installed U value include:
Air Leakage
Air leakage is often more important than the insulation value of the curtain itself.
Even a highly insulated curtain can perform poorly if warm air escapes around:
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side guides
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bottom rails
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head details
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surrounding structure
This is particularly important in:
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high traffic openings
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windy locations
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temperature-controlled environments
Frequency of Use
A door can only insulate effectively when it is closed.
If an opening remains open for long periods:
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heat loss increases dramatically
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airflow becomes uncontrolled
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theoretical U values become less relevant
This is one reason why high speed doors can often outperform slower doors operationally, even if the static curtain insulation appears similar on paper.
Installation Quality
The same shutter installed differently may produce different results.
Performance is influenced by:
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guide alignment
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sealing details
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fixing method
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building condition
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interface gaps
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reveal condition
Poor installation can significantly reduce real-world thermal performance.
Thermal Bridging
Heat naturally transfers through conductive materials such as steel and aluminium.
Areas such as:
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guides
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brackets
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support steelwork
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fixing points
can all create thermal bridges which increase heat transfer.
Building Condition
The surrounding building fabric matters enormously.
A well-insulated shutter installed into:
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damaged cladding
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leaking roof junctions
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poorly sealed openings
may deliver limited overall improvement.
In many industrial buildings, the opening perimeter itself and external doorways is often a major source of uncontrolled air leakage.
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How Is a U Value Calculated?
A simplified relationship is:
U=1RU = \frac{1}{R}U=R1​
Where:
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U = heat transfer
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R = thermal resistance
The greater the thermal resistance:
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the lower the heat transfer
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the better the insulation
What Is an R Value?
R value measures resistance to heat flow.
Unlike U values:
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higher R values are better
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higher resistance means less heat transfer
For example:
R=1UR = \frac{1}{U}R=U1​
The two figures are directly related.
Simple Example
If a material has:
R=1.1 m2K/WR = 1.1\ \mathrm{m^2K/W}R=1.1 m2K/W
Then:
U=11.1≈0.91 W/m2KU = \frac{1}{1.1} \approx 0.91\ \mathrm{W/m^2K}U=1.11​≈0.91 W/m2K
Again, this does not automatically mean the complete installed shutter achieves this value.
Typical U Values of Common Building Materials
The figures below are approximate and vary depending upon construction method and thickness.
Material / ConstructionApproximate U Value:
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Single glazed window5.0 – 6.0 W/m²K
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Uninsulated roller shutterTypically very poor thermal performance
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Older cavity wall1.5 – 2.0 W/m²K
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Modern insulated cavity wall0.18 – 0.30 W/m²K
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Insulated sectional door1.0 – 1.8 W/m²K
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Insulated roller shutter curtain (lath only equivalent)Often around 0.9 – 1.5 W/m²K equivalent
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High-performance cold store panels0.15 – 0.25 W/m²K
These examples help illustrate that industrial door performance sits within a much wider building insulation picture.
Why Air Leakage Often Matters More Than U Value Alone
One of the biggest misconceptions is assuming a low U value automatically guarantees low heat loss.
In industrial environments:
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uncontrolled airflow
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open door time
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pressure differences
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stack effect
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traffic movement
can often have a greater impact on energy loss than the insulation value of the curtain itself.
This is why:
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high speed operation
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environmental separation
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good sealing
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reducing open time
are often just as important as the quoted insulation figure.
The Most Important Question:
“How Will the Door Perform in Real Operation?”
When assessing industrial doors, the real focus should not simply be: “What is the quoted U value?”
It should be:
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How often is the opening used?
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How long does it remain open?
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How much air leakage exists?
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How good is the installation?
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How stable are the surrounding environmental conditions?
These factors often determine actual energy performance far more than a single headline figure. This is one of the reasons why many businesses reviewing potential ROI Savings now focus not only on insulation values, but also on opening exposure time, environmental separation and operational efficiency within real-world industrial environments.
Understanding the Whole Picture
Improving thermal performance is not simply about choosing the lowest quoted U value.
Real-world energy efficiency depends on how the complete door system performs once installed and operating within your building environment.
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Factors such as air leakage, open time, traffic levels, installation quality, sealing and environmental control often have just as much impact as the insulation value of the curtain itself.
We are always happy to offer practical advice and guidance when reviewing industrial openings, reducing heat loss and improving environmental control.
If you would like to discuss your application, arrange a site visit or better understand the options available, please contact us.
Energy Saving Doors
25 Britannia Square
Worcester
Worcestershire
WR1 3DH
United Kingdom
+44 1905 317878