If you manufacture or install windows, doors, rooflights, or lanterns, you’ve probably noticed the same thing across recent projects:

U-value targets are getting tighter.

Between Part L updates, SAP 10 modelling soon to be the new Home Energy Model HEM, and the upcoming Future Homes Standard, architects and specifiers are pushing glazing systems harder than ever.

For many systems, especially large glazed openings, achieving those numbers isn’t always straightforward.

And the pressure is only increasing.

The Reality for Modern Glazing Systems

Large areas of glazing are now standard in residential and commercial design.
We see it everywhere:

• Bi-fold doors across entire walls
• Large sliding doors
• Glass lanterns and flat rooflights
• Floor-to-ceiling glazing

Architects want maximum glass and minimal frame.
At the same time, regulations demand better thermal performance than ever before.
That combination creates a challenge.
The bigger the glazing area, the more important the glass performance becomes.

Why Triple Glazing Isn’t Always the Answer

Traditionally, when a project needed lower U-values, the solution was simple:

Upgrade to triple glazing.

But anyone working with large door systems or roof glazing knows the problems this can create.

Weight

Triple glazing is heavy. On large sliding or folding doors, that weight quickly becomes a problem.
It can affect:

• hardware performance
• long-term reliability
• ease of operation

Thickness

Most triple glazed units are 36mm to 54mm thick.
Many systems simply weren’t designed for that depth.
For example:

• bifold door systems often max out around 28mm
• some sliding systems around 36mm
• lanterns and rooflights can have strict weight limits

That means designers are often forced to choose between:

• meeting the U-value target, or
• keeping the chosen system.

Where Thin Triple Glazing Comes In

This is exactly the problem modern glazing technology is solving.

Crystal Units’ C.U.in technology uses a suspended film inside a double glazed unit to create an additional insulating chamber.

In simple terms:

It delivers triple-glazing thermal performance, without needing three panes of glass.
That means you get the insulation benefits without the bulk or weight.

Triple Glazing Performance – Double Glazing Size

Because of this design, C.U.in units are:

• Up to 36% thinner than traditional triple glazing
• Up to 33% lighter
• Compatible with standard double-glazed frames and hardware

Centre pane U-values can reach as low as 0.2 W/m²K, which is significantly better than most conventional glazing options.

For installers and manufacturers, this solves a very practical problem:

You can hit low U-values without redesigning the whole system.

Real Projects Where Thickness Matters

This kind of solution becomes especially valuable in projects with strict system limits.
For example:

At Elmsbrook House, triple-glazed performance was required for Schuco folding doors — but the system could only accept a 28mm unit.

Using C.U.in glazing allowed the project to achieve the required thermal performance without changing the door system.

In another project, The Forge development, the façade system allowed only 36mm units, yet the required U-values were still achieved using C.U.in.

These situations are becoming increasingly common as energy targets tighten.

Independent Testing Shows Real Performance

Performance improvements aren’t just theoretical.

Testing at the University of Salford Energy House compared C.U.in glazing with standard double glazing.

The results showed heat loss through the centre of the glazing was:

• 5.4 times lower than E-rated double glazing
• 2.5 times lower than A-rated double glazing.

Across the whole building, installing C.U.in glazing also reduced total heat loss compared with conventional glazing systems.

Why This Matters for Rooflights and Lanterns

Roof glazing has its own challenges.

Flat rooflights and lanterns often face strict limits on:

• glass weight
• frame capacity
• structural loading

Using traditional triple glazing in these systems can quickly increase loads.

Thin triple glazing gives designers another option:

high thermal performance without the extra mass.

Lower Carbon as Well as Lower U-Values

Beyond energy performance, carbon impact is becoming part of the conversation.

Because C.U.in uses less glass than traditional triple glazing, it also reduces manufacturing emissions.

Switching from triple glazing to C.U.in can reduce production carbon by around 8 kg CO₂ per square metre of glazing.

And lifecycle studies have shown heating demand reductions of 23–45% compared with standard glazing systems.

What This Means for the Industry

As regulations continue to tighten, glazing will play an even bigger role in meeting energy targets.
For manufacturers and installers, the challenge will be balancing:

• performance
• weight
• thickness
• compatibility with existing systems

Thin triple-glazing technologies are increasingly becoming the practical solution.

They allow the industry to deliver better insulation without compromising the systems that architects and homeowners want.

And with large glazed openings continuing to grow in popularity, that balance is more important than ever.