How Thermal Breaks Work in Architectural Glazing

Thermal breaks in architectural glazing perform much of their work out of sight. They sit within aluminium frames and fixing profiles, interrupting the movement of heat through metal while the finished glazing remains visually quiet.

Their importance follows directly from one of aluminium's defining properties. Aluminium is strong, accurate and well suited to the slender framing required for large areas of architectural glass. It is also highly conductive.

Where aluminium creates a continuous connection between the internal and external sides of a building envelope, heat can travel through that connection readily. A thermal break interrupts the route.

IQ Glass developed Invisio+ around this principle. Invisio+ is a thermally broken structural glazing fixing system for large-scale frameless glass. The fixing remains concealed within the surrounding building fabric, while the integrated thermal break improves the performance of a junction that would otherwise provide a conductive path through the envelope.

The result provides a useful example of how thermal breaks work in architectural glazing, particularly where the visible architecture depends on making the supporting frame disappear.

What Is a Thermal Break in Architectural Glazing?

A thermal break is a section of low-conductivity material incorporated within a metal frame or fixing profile to reduce heat transfer through it.

Without thermal separation, an aluminium component can provide a continuous conductive route through the building envelope. Heat reaching one side of the profile can travel through the metal towards the other.

The thermal break divides that route.

Internal and external aluminium components remain structurally connected as part of the complete system, while the lower-conductivity material between them reduces the rate at which heat passes through the frame.

The principle works throughout the year.

During cold external conditions, thermal separation reduces heat travelling from the heated interior towards the outside.

During hot external conditions, it reduces heat travelling through the framing towards the cooler interior.

The same detail also influences internal surface temperatures around the glass. A better thermally separated frame can maintain a warmer internal surface during winter conditions, helping to reduce localised cold spots and condensation risk at the glazing perimeter.

Why Aluminium Requires Thermal Separation

Aluminium has become fundamental to modern architectural glazing because it can support substantial loads within relatively compact profiles.

It allows large panes, narrow sightlines, concealed frames and precise junctions to be engineered with considerable accuracy.

Its thermal conductivity has to be addressed within the same design.

A continuous aluminium profile passing through an insulated envelope creates a thermal bridge. Energy can travel through the metal more readily than through the insulated areas surrounding it.

This becomes particularly relevant as the performance of the glass itself improves.

A high-performance double or triple-glazed unit may have an excellent centre-pane U-value, but the completed facade includes much more than the centre of the pane. Frame profiles, perimeter conditions, structural fixings and connections with the surrounding building fabric all contribute to the overall thermal performance.

The glazing and its fixing therefore need to be considered as one envelope.

Thermal Bridging at a Structural Glass Fixing

Frameless structural glazing creates an especially interesting condition because the structural work is deliberately concealed.

A large pane may appear to rise directly from the finished floor. In reality, the glass requires a substantial fixing below the surface.

Traditional structural glass details can use metal angles around the base of the pane. Where those metal elements create a continuous route through the fixing, they also create a route for heat transfer.

The heat path can be traced very clearly through a section drawing. Energy reaches the internal metal angle, passes through the connected aluminium and continues towards the external side.

The finished glazing may look frameless. Thermally, the concealed fixing still exists.

Invisio+ integrates the thermal break directly through this fixing zone, interrupting the conductive route within the profile itself.

This is the essential logic behind a thermal break: identify the metal path through which heat can travel, then introduce thermal separation without compromising the structural role of the system.

Invisio+ and Thermally Broken Structural Glazing

Structural glazing depends on substantial engineering within details that are often almost invisible once construction is complete.

Invisio+ was developed by IQ Glass as a thermally broken fixing system for large-scale frameless structural glass.

The glass is held within the channel of the profile. The fixing itself is recessed into the adjacent construction and concealed beneath the surrounding finishes.

Within that concealed zone sit three important elements:

• the structural fixing
• the high-performance glazed unit
• the integrated thermal break

Together, they allow the glass, fixing and thermal performance to be developed as one detail.

Invisio+ has been tested at 3 m wide by 6 m high.

With Ug 0.7 W/m²K triple glazing, the tested system achieved a Uw of 0.5895 W/m²K.

Those dimensions place the system firmly within large-scale architectural glazing. A 6 m high structural glass panel creates very different demands from a conventional domestic window, both structurally and thermally.

The purpose of Invisio+ is to provide the required fixing performance at that scale while preserving the clean appearance expected from frameless structural glass.

Why Invisio+ Accommodates Deeper Glass Build-Ups

Invisio+ develops the original Invisio fixing concept to accommodate deeper glazing specifications, including triple glazing.

The change reflects the increasing performance requirements being placed on contemporary glass elevations.

A modern architectural glass build-up may contain several functional layers. Insulated cavities, laminated panes, specialist coatings, low-emissivity coatings and other components all contribute to the final thickness and performance of the unit.

Triple glazing increases that depth further.

The fixing system must provide sufficient capacity for the glass while maintaining structural support, thermal performance and the intended junction with the surrounding finishes.

Invisio+ provides the deeper channel required for these build-ups and integrates thermal separation within the frame.

This allows large-scale frameless glazing to use the more substantial glass specifications required on high-performance building envelopes.

Triple Glazing and Thermal Breaks

Triple glazing and thermal breaks operate in different parts of the same facade.

The triple-glazed unit reduces heat transfer across the transparent area.

The thermal break reduces conductive heat transfer through the aluminium fixing.

Their performance is connected at the perimeter of the glass.

This relationship is one reason a glazing specification should consider the complete system rather than relying solely on the centre-pane value of the glass.

The glass may occupy almost the entire visible elevation, while the structural fixing is concentrated around its edges. Both still form part of the route between the interior and exterior.

Invisio+ combines a thermally broken fixing with the capacity for deeper triple-glazed units, allowing these two parts of the envelope to be developed together.

How Thermal Breaks Perform in Cold Weather

Cold weather creates the most familiar heat-transfer condition.

The internal environment is heated and the exterior is colder. Heat naturally travels towards the lower-temperature environment.

An uninterrupted aluminium fixing makes that journey easier.

The thermal break increases resistance through the frame and reduces the rate at which heat travels across the fixing.

Internal surface temperature is important here as well.

Metal surfaces that become significantly colder than the surrounding room can create localised areas where condensation is more likely to form. This becomes particularly relevant in spaces with elevated humidity and around extensive glazed elevations.

The perimeter detail therefore has a direct relationship with comfort as well as energy performance.

A high-performing pane deserves an equally considered edge condition.

How Thermal Breaks Perform in Hot Weather

During hot weather, the temperature relationship can reverse.

External aluminium exposed to high temperatures can conduct heat towards a cooler interior. The thermal break reduces this conductive route in exactly the same way.

For highly glazed architecture, this sits alongside a wider summer-performance strategy.

Solar control glass can reduce the solar energy passing through the transparent glass area. External shading, orientation, ventilation and cooling strategies can contribute further.

These measures address different parts of the problem.

Solar control coatings manage solar radiation passing through the glass.

Thermal breaks reduce conduction through the aluminium framing and fixing components.

Large architectural elevations can require both.

Keeping the Engineering Concealed

The architectural value of structural glazing often lies in the apparent absence of structure.

Invisio+ is designed around that requirement.

The glass sits within the fixing channel and the profile is concealed within the surrounding floor, wall or other building finishes. The visible elevation can therefore retain the character of frameless structural glass.

The thermal break sits inside the same concealed assembly.

This allows additional thermal engineering to be introduced without adding a prominent frame around the glass.

The finished detail remains restrained because the complexity has been resolved inside the building fabric.

This is common to much of high-end architectural glazing. Simple-looking junctions usually depend on a considerable amount of design work behind the finished surface.

Designing Structural Glass for Future Replacement

Invisio+ also considers access to the glass after installation.

A cover within the fixing profile can be moved to reveal the mechanical fixings below. Releasing those fixings allows the retaining section of the profile to be removed.

The glazed unit can then be taken out without unnecessarily damaging the surrounding finishes.

This becomes particularly useful with oversized panes and highly finished interiors, where destructive access around the perimeter of the glazing would create significant additional work.

Glass replacement is part of the life of a facade. Designing access into the fixing from the outset makes future intervention more controlled.

The detail may remain hidden for years. It still needs to work when somebody eventually has reason to open it.

Why Thermal Breaks Matter in Large-Scale Glazing

The scale of structural glass can make small areas of detailing disproportionately important.

A 6 m high pane may read as one uninterrupted sheet of glass. Its perimeter has to perform several jobs simultaneously.

The fixing must:

• support the structural glass
• accommodate the required glass depth
• resist the relevant loads
• integrate with the building structure
• contribute to air and weather performance
• maintain the required thermal separation
• coordinate with the surrounding finishes
• allow appropriate access and replacement

These requirements meet within a relatively compact section of construction.

Thermal breaks in architectural glazing therefore sit within the broader discipline of facade engineering. Their effectiveness depends on how they relate to the glass, fixings, structure and surrounding envelope.

The best results come from resolving these relationships early.

Specifying Invisio+ for Frameless Structural Glass

Invisio+ is designed for projects where large-scale structural glass needs to combine a frameless appearance with high levels of thermal performance.

Typical applications may include projects requiring:

• oversized frameless structural glass
• triple-glazed structural glass
• concealed base fixing
• thermally broken framing
• high-performance building envelopes
• clean floor and wall junctions
• future access for glass replacement

The system can be developed around the specific glass build-up and structural requirements of the project.

Early coordination is valuable because the glazing detail can influence floor construction, structural support, drainage, glass thickness and adjacent finishes.

IQ Glass works with architects and project teams to develop these interfaces as part of bespoke structural glazing packages.

How Thermal Breaks Work in Architectural Glazing

Thermal breaks reduce conductive heat transfer through aluminium frames by interrupting the direct metal connection between the internal and external sides of the glazing system.

Their contribution is largely hidden within the finished architecture.

Invisio+ applies this principle to the fixing of large-scale frameless structural glass. Its integrated thermal break reduces heat transfer through the concealed base profile, while the deeper channel accommodates high-performance glass build-ups including triple glazing.

The system has been tested at 3 m wide by 6 m high, achieving a tested Uw of 0.5895 W/m²K with Ug 0.7 W/m²K triple glazing.

Alongside that thermal performance, the concealed profile preserves the frameless appearance of the glass and allows the retaining section to be removed for future glass replacement.

The physics of a thermal break is simple. The quality of an architectural glazing system lies in how thoroughly that principle has been carried through the detail.

Looking to transform your space? Contact the IQ Glass technical team to discuss Invisio+, thermally broken structural glazing or a bespoke high-performance glass specification.