Structural Glazing

Structural Glass Dimensions: Size and Specification Guide

Structural glass dimensions are not set by a single “maximum size” chart. On a real architectural glazing project, the size of each pane is the result of several factors working together: what can be manufactured, what can be engineered safely, and what can realistically be transported, lifted and installed on site.

This technical advice article explains how IQ Glass approaches structural glass dimensions. It is written for architects and contractors who want clear, realistic guidance for frameless glass walls, roofs, floors and oriel windows, without digging through raw test tables.

How big can structural glass actually be?

At the manufacturing end, modern flat glass (toughened glass) production can achieve extremely large sheets. Current capabilities for flat glass are:

• Up to approximately 21 m x 3.2 m for coated glass
• Up to approximately 21 m x 3.5 m for uncoated glass

On paper, that’s a very generous starting point.

On a live project, the limits are then set by access and replacement: roads, site access, cranes, glazing robots, future replacement strategy

IQ therefore does not talk about structural glass dimensions in isolation. We look first at how each pane is supported, which loads it must carry and what route exists from factory to final position. Only once those points are understood does a “maximum size” become meaningful.

Further reading: What is Structural Glass & Structural Glazing?

Invisio® test data and proven sizes

Invisio® is IQ’s own structural glazing fixing system. It is a fully thermally broken glazing fixing system designed to hold insulated structural glass units with a completely frameless finish. All aluminium profiles are hidden by building finishes, so there are no visible frames or cappings.

Unlike ad hoc steel angle solutions, Invisio has been modelled and tested across a series of standard situations that cover:

• Four‑edge supported frameless picture windows
• Multi‑pane structural glass walls and façades
• Oriel windows and glass links
• Rooflights and glass roofs
• Walk‑on glass floors and floorlights

For each type of installation the system has been tested at different wind pressures with strict limits on the allowed deflection. Joints between panes are structurally silicone‑bonded, with no internal glass mullions needed at the glass joints. This gives hard numbers for proven configurations, rather than relying only on experience or rules of thumb.

Key Invisio test figures (simplified)

• Four‑edge supported frameless window
  Height up to 5.0 m; width up to 6.9 m at 0.8 kN/m²; width up to 3.45 m at 1.6 kN/m²
• Multi‑pane structural glass wall or façade
  Tested up to 5.0 m in height, with total wall widths in the Invisio test series up to 12.71 m at 0.8 kN/m² and up to 6.88 m at 1.6 kN/m²
• Oriel window or glass link
  Height up to 5.0 m; width up to 5.74 m at 0.8 kN/m²; width up to 2.87 m at 1.6 kN/m²
• Frameless rooflight in Invisio roof profile
  A single rooflight unit up to 1.5 m x 3.0 m in one pane
• Walk‑on floorlight in Invisio floor profile
  Max pedestrian loads up to 1.83 kN/m², based on the tested Invisio floorlight system

These are proven reference sizes. On a project we either:

• keep the glass within these limits, or
• where the architecture requires larger spans, carry out additional project‑specific engineering to justify the increase.

Further reading: Invisio® Structural Glazing System

Roofs, rooflights and walk‑on floors

Many of the most detailed questions about maximum structural glass dimensions relate to glass roofs and glass floors rather than walls.

Glass roofs and rooflights

There are two broad approaches:

1. Individual rooflight units
• Single insulated units, supported on all four edges by a thermally broken T-section (like Invisio)
• Common sizes in design: about 1.2–1.5 m wide by up to 3.0 m long in a single pane depending on access
• Used as one‑off rooflights or as a series of repeated units
2. Larger structural glass roofs
• The “whole” roof is formed from a series of panes joined with structural silicone
• Structural support is provided by laminated low‑iron glass beams, slim steel sections or carefully detailed timber below the joints

On some projects we use bespoke glass beams that interlock into precision‑cut notches in the inner face of the glass wall, so they do not rely on visible vertical fins. This provides lateral support to the roof without adding posts or mullions into the line of sight and allows spans of several metres to be achieved with clear, structural glass beams sized to suit the loads.

Typical roof load cases used in testing include:

• Snow load around 1.26 kN/m² for flat roofs
• Snow load around 2.02 kN/m² for roofs at 45° pitch

(For drainage and upstand details, see IQ’s technical guidance on structural glass roofs and rooflight design.)

Walk‑on glass floors and floorlights

Walk‑on glass floors bring a different set of considerations. The glass must carry:

• pedestrian traffic
• furniture and maintenance loads
• in some cases, significant thermal and acoustic requirements

The Invisio floorlight profile is thermally broken, so external floorlights above habitable spaces can achieve good insulation as well as strength.

As a guide:

• Along open edges, a glass beam‑to‑balustrade detail can be used, where one laminated glass element acts both as the floor support and the balustrade, with the floor units structurally bonded to it. The result is a single all‑glass edge with no steel channels or posts interrupting the view.

The exact glass thickness and build‑up are designed to the loading class specified by the project engineer (for example, domestic, commercial or public assembly).

Further reading: Glass Floors by Invisio® – Structural Glass Floors

Thickness, thermal performance and the fixing system

The visible height and width of a pane are only half the story; the other half sits in the edge: the glass build‑up and the glazing fixing system.

Invisio is fully thermally broken. The profiles incorporate a polyamide thermal break and have been modelled to achieve overall Uw values in the region of 1.1–1.2 W/m²K when paired with typical double‑glazed units.

Glass thickness increases as spans, loads and performance targets increase:

• A modest frameless window may use a relatively slim insulated unit
• Larger façades, roofs and walk‑on floors use deeper glass build‑ups with thicker toughened panes, multiple laminates and, where required, triple glazing

The standard Invisio profile is designed to accommodate substantial double‑glazed units; the Invisio+ profile accepts even deeper units. This means pane sizes do not have to be reduced purely because the glass specification needs to work harder.

• Typical Ug values for high‑performance double glazing are around 1.1 W/m²K
• Combined with Invisio, typical overall Uw values are around 1.1–1.2 W/m²K

Further reading: Roof Glazing Thermal Performance

How IQ sets structural glass sizes on a live project

Behind the scenes, the sizing process follows a clear sequence:

1. Start with the architecture
   Plans, sections, elevations and visuals are reviewed to understand which views and alignments matter most, which areas are intended to feel as open and uninterrupted as possible, and where joints or supports could sit without undermining the concept.
2. Match each glazed area to tested conditions
   A frameless window, a glass wall, an oriel, a rooflight and a floor each correspond to different test conditions or historical completed projects. This indicates what has already been modelled and proven under similar loads.
3. Apply project‑specific loads
   Site exposure, building height, wind and snow loads, pedestrian and barrier loads are applied, and the glass build‑up is adjusted to suit.
4. Check access and logistics
   There is little value in designing a 5 m x 3 m pane if it cannot reach the opening because of a low bridge or a tight courtyard. Alternative joint patterns or sequences of panes are proposed where needed to achieve the same visual effect with dimensions that are realistic to handle and, if necessary, replace.
5. Fix the agreed dimensions into detailed drawings
   The agreed structural glass dimensions are fixed into CAD details, interface drawings and performance summaries to support specification, planning submissions, contractor coordination, manufacture and installation.

The aim is not to chase extreme sizes for their own sake. It is to use the capability of structural glazing to remove unnecessary transoms, mullions and frames, while staying firmly within the boundaries of sound structural and thermal design.

Next steps

If you are at an early design stage and want to know whether a particular opening or façade is realistic, you do not need to arrive with all of the figures.

A plan, a section and a clear sense of what you are trying to achieve are usually enough for an initial technical conversation about structural glass dimensions. From there, the IQ technical team can:

• suggest sensible maximum heights and widths for each area
• outline likely glass build‑ups and fixing approaches
• highlight where glass beams or slim steelwork may be required

To discuss structural glass dimensions on your project, contact us now or email your drawings to hello@iqglassuk.com.