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:
🟢 One manufacturer may quote the thermal performance of the insulated lath itself
🟢 Another may quote the calculated U-value of the complete installed shutter
🟢 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:
🟢 The better the insulation
🟢 The lower the heat loss
🟢 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.
Lath U-Value versus Door U-Value
1. The U-Value of the Insulated Lath
An insulated roller shutter curtain is constructed from individual insulated laths.
Manufacturers may test or calculate the thermal performance of the lath itself, rather than the complete shutter assembly.
For example, a foam-filled insulated lath may have a quoted thermal resistance of approximately:
R = 1.1 m²K/W
This figure relates only to the insulated lath profile. It does not represent the thermal performance of the complete installed roller shutter.
It does not take into account:
🟢 Guide rails
🟢 Bottom rail
🟢 Shutter box
🟢 Air leakage around the curtain
🟢 Installation quality
🟢 Gaps around the opening
🟢 Thermal bridging
🟢 Operational movement of the shutter
A useful comparison is quoting the insulation performance of an individual building material without considering the thermal performance of the complete wall or building envelope.
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:
🟢 The complete shutter assembly
🟢 The installation method
🟢 The surrounding structure
🟢 Air leakage
🟢 Thermal bridging
🟢 Operational tolerances
The U-value of the complete installed shutter is therefore usually:
🟢 Higher than the lath-only figure
🟢 More representative of real-world thermal performance
🟢 More complex to calculate accurately
Ultimately, it is the thermal performance of the complete installed shutter, rather than the insulated lath alone, that determines its contribution to overall building heat loss.
Why Similar Doors Perform Differently
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 can be as important as, and sometimes more important than, the insulation value of the curtain itself.
Even a highly insulated curtain can perform poorly if warm air escapes around:
🟢 Side guides
🟢 Bottom rail
🟢 Head details
🟢 Surrounding structure
This is particularly important in:
🟢 High-traffic openings
🟢 Exposed or windy locations
🟢 Heated warehouses
🟢 Temperature-controlled environments
Frequency of Use
A door can only provide its full insulation benefit when it is closed.
If an opening remains open for extended periods:
🟢 Heat loss increases significantly
🟢 Airflow becomes uncontrolled
🟢 Static U-values become less relevant to overall energy performance
This is one reason why high-speed doors can offer significant operational energy benefits compared with slower doors. By reducing the amount of time the opening remains exposed, they can help limit uncontrolled air exchange and heat loss.
Installation Quality
The same shutter installed in different conditions may produce different levels of thermal performance.
Performance can be influenced by:
🟢 Guide alignment
🟢 Sealing details
🟢 Fixing methods
🟢 Building condition
🟢 Interface gaps
🟢 Reveal condition
Poor installation can significantly reduce the real-world thermal performance of the complete door assembly.
Thermal Bridging
Heat can transfer through conductive materials such as steel and aluminium.
Potential thermal bridges include:
🟢 Guides
🟢 Brackets
🟢 Support steelwork
🟢 Fixing points
These components can provide pathways for heat transfer, reducing the overall thermal performance of the installed shutter.
Building Condition
The performance of the surrounding building fabric is also important.
A well-insulated shutter installed within an opening affected by:
🟢 Damaged cladding
🟢 Leaking roof junctions
🟢 Poorly sealed openings
may deliver only limited improvement to the overall thermal performance of the building.
For this reason, door insulation should be considered as part of the complete building envelope rather than in isolation.
In many industrial buildings, the opening perimeter itself and external doorways is often a major source of uncontrolled air leakage.
How Is A U-Value Calculated?
A simplified relationship is:
U = 1 ÷ R
Where:
🟢 U = Thermal transmittance (U-value)
🟢 R = Thermal resistance (R-value)
The greater the thermal resistance:
🟢 The lower the heat transfer
🟢 The better the insulation
What Is an R-Value?
R-value measures a material or assembly’s resistance to heat flow.
Unlike U-values:
🟢 Higher R-values indicate better insulation
🟢 Higher thermal resistance means less heat transfer
The relationship can also be expressed as:
R = 1 ÷ U
Simple Example
If a material has:
R = 1.1 m²K/W
Then:
U = 1 ÷ 1.1 ≈ 0.91 W/m²K
However, this calculation relates only to the material or element represented by the R-value. It does not automatically mean that the complete installed shutter achieves a U-value of 0.91 W/m²K.
Typical U-Values Of Common Building Materials
The figures below are approximate and vary depending upon construction method and thickness.
Material / Construction — Approximate U-Value
🟢 Single-glazed window: 5.0–6.0 W/m²K
🟢 Uninsulated roller shutter: Typically very poor thermal performance
🟢 Older cavity wall: 1.5–2.0 W/m²K
🟢 Modern insulated cavity wall: 0.18–0.30 W/m²K
🟢 Insulated sectional door: 1.0–1.8 W/m²K
🟢 Insulated roller shutter curtain (lath-only equivalent): Often around 0.9–1.5 W/m²K
🟢 High-performance cold-store panels: 0.15–0.25 W/m²K
These figures are indicative only. Actual U-values depend on construction, testing methodology and whether the figure relates to an individual component or the complete installed assembly.
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, the following can often have a greater impact on energy loss than the insulation value of the door curtain itself:
🟢 Uncontrolled airflow
🟢 Door open time
🟢 Pressure differences
🟢 Stack effect
🟢 Traffic movement
This is why overall doorway performance should consider:
🟢 High-speed operation
🟢 Effective environmental separation
🟢 Good sealing
🟢 Reduced door open time
These factors can be just as important as the quoted insulation value when assessing real-world energy performance.
The Most Important Question:
“How Will the Door Perform in Real Operation?”
When assessing industrial doors, the focus should not simply be:
“What is the quoted U-value?”
It should also consider:
🟢 How often is the opening used?
🟢 How long does it remain open?
🟢 How much air leakage occurs?
🟢 How well is the door installed and sealed?
🟢 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.
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