Structural glazing is a façade glazing technology in which insulated glass units are attached to the supporting frame in a concealed way, with no visible aluminum profiles on the exterior. From the outside, the building appears as a seamless glass surface. This approach makes it possible to create impressive panoramic façades, but it requires a high level of expertise at every stage — from design to installation.
In this article, I’ll cover the technical specifics of structural glazing, the common mistakes made during its implementation, and how to avoid them. I’ll also share practical experience working with operable elements — windows, doors, and folding systems — in structural configurations.
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What Is Structural Glazing and How It Work
Structural glazing is based on a mullion-transom system. Vertical mullions and horizontal transoms form the load-bearing framework that carries the weight of the glass and resists wind loads. The key difference from conventional systems lies in the method of attaching the glass units.
In a standard mullion-transom façade, insulated glass units are clamped with exterior pressure plates that remain visible. In a structural system, the attachment is concealed — using special embedded fixing elements and structural silicone sealant.
Structural IGUs: What Makes Them Different
The key difference of structural glazing units is in their manufacturing technology:
Sealant. Standard glazing units use polysulfide sealant, which is susceptible to ultraviolet radiation and must be covered by a profile. Structural glazing units use silicone sealant, which is resistant to UV radiation and atmospheric influences.
Sealing depth. In regular glazing units it is 4-6 mm, in structural ones — 18-20 mm. This depth is necessary to accommodate embedded profiles.
Embedded elements. Special fastening elements are glued into the glazing unit sealant — plastic or aluminum parts approximately 100 mm in size, which in the installation environment are called «helicopters». These are what provide the hidden attachment of the glazing unit to the supporting structure.
Installation is carried out with a special key that rotates the helicopter and fixes it in the embedded profile of the glazing unit. High precision positioning of the embedded elements in the sealant is required — for this purpose, special templates are used in production.
The cost of structural glazing units is 50% or more higher than regular ones. This is due to the use of expensive silicone sealant, special embedded elements and manufacturing complexity.
Installing Structural Glazing
Common Mistakes When Applying Sealant
The main problem of structural glazing is the difficulty of quality sealant application. People without appropriate qualifications often make mistakes:
- apply too thin a layer of sealant that collapses when pressed;
- create unevenness, sagging and drips;
- leave air inclusions that reduce the strength of the connection.
If the installers do not have experience in performing structural joints, I recommend contacting specialized teams or sealant suppliers. Professional installers use special techniques: masking with painter’s tape, processing with a spatula, using a sponge with soapy solution, or rubbing sagging with zero sandpaper.
Sealing structural joints beautifully is work that requires special skills and tools. Do not save on the qualifications of installers, otherwise you will have to redo it.
Operable Elements in Structural Glazing
Structural glazing makes it possible to integrate operable elements such as windows, doors, and folding systems. However, classic sliding systems cannot be made structural. The only exception is the innovative magnetic-levitation system developed by Thermoglass, which allows the creation of large sliding elements based on high-rigidity insulated glass units with carbon spacer bars.
For structural windows and doors, the sash is manufactured with a “tooth” — an extension of the exterior glass that is bonded into the sash. The frame must also have glass strips approximately 50 mm wide. This introduces a number of technical nuances that are important to understand.
Glass Selection: A Critical Decision
When using soft multifunctional coating, manufacturers cannot properly paint the glazing unit tooth without first removing the coating. Removing the coating leads to visible stripes from the grinding wheel, which spoils the appearance.
Alternative blackening with sealant creates a golden tint on the edges due to the coating. However, no one will make glass strips for the frame with soft coating — manufacturers will not cut them with the coating.
I tried to match the painting of a regular strip to the golden tint of the tooth with coating. We went through about 20 different shades with the addition of mirror finish — nothing worked. The tint that the coating provides is so individual that it is impossible to match the color of the strip.
My solution: I only use HD coating (hard solar control) for structural opening elements. Its advantage is that glazing unit manufacturers can paint it without removing the coating on professional painting lines. They can paint both the glazing unit tooth and the strip from the same glass with coating — then you get a perfect match of shades.
Examples of HD coatings: Silver 32, Silver 70 and others. If you see two numbers separated by a slash (for example, 60/40) — this is multifunctional soft coating. If one number — it’s most likely HD, but it’s better to check with the manufacturer.
In this case, we make solar control glass on the outside and energy-saving glass on the inside. If you have a double-chamber glazing unit, you can install two energy-saving glasses — the thermal characteristics will be no worse than with multifunctional.
Glass Strips: Length Limitations
HD glass strips with painting on automatic lines can be up to 2 meters long. If you have a 3-meter high door, it will be a joint of two strips. But this is still better than making a solid strip from different glass without coating, which will differ in shade.
For vent sashes, where there is no transparent part, regular raw glass with painting can be used. In this case, the effect of shade difference is not so noticeable. There are companies that specialize in small products (mirrors, interior glass) and can make strips 40 mm wide up to 3200 mm long as solid pieces with polished edges.
Important! In all structural elements — in strips and glazing unit teeth — edges must be polished, because they are visible. Not just grinding, but polishing.
Handle Installation: Preventing Chipping
When installing handles in structural glass, it is necessary to provide:
- holes of larger diameter than standard ones;
- mandatory chamfer on the edges of holes to prevent chipping;
- special plastic bushings made on a 3D printer.
I had cases when during sash adjustment the handle played slightly, hit the edge of the hole, and the glazing unit cracked. Bushings protect the glass and transfer the load from the handle directly to the profile, bypassing the glass.
Around each hole in production, double-sided tape must be glued, and spacers are installed between the profile and the handle. This eliminates pressure on the glass.
Structural Door Nuances
For doors with concealed hinges, it is mandatory to make a chamfer on the frame strip located on the hinge side. Without a chamfer, when opening, the sash will catch on the strip. With a chamfer, the gap can be reduced from 12 mm to 7 mm.
When using roller hinges, milling on the glass along the edge will be required — this is also solvable in production.
Vent Sashes: A Special Case
A vent sash is a narrow aluminum solid sash with a width of 180 or 280 mm, which is usually installed on the side of a large window for ventilation.
In Alutech system solutions, glass is glued only to the sash, while the frame remains without glass — this looks unattractive because the frame profile is visible from the outside. If you want a completely glass effect from the outside, you need to glue a strip of glass to the sash and 4 strips to the frame.
Here you can use regular raw glass with painting, because there is no transparent part for comparing shades. For vent sashes over 2 meters high, you will have to make strip joints.
Important nuances of vent sashes:
- When opening inward, the glass on the sash can catch on the frame — you need to make a chamfer on the sash glass on the handle side.
- You need to think through the attachment to the mullion-transom system from the inside, as the glass strips on the outside will not allow screwing the sash in the usual way.
- The vent sash frame must be rigidly fixed to the mullions or through aluminum compensators, otherwise when closing it will play and gaps will appear.
Problem with painting strips: sealant can pass through the paint — visible stripes appear. Solution: after painting, apply a protective lacquer coating on top so that the sealant does not come through.
Drainage in Structural Systems
Since glass is glued on the outside, it is necessary to think through drainage. If it is possible to make it hidden (under the sill, in the base profile) — make it hidden. Then there is no need to make holes in the strip.
If the product goes to the floor and drainage cannot be made hidden, round or oval longitudinal drainage holes need to be milled in the lower glass strip.
Glass Bonding Technology
After manufacturing the sash and receiving painted glazing units with tooth and glass strips, the gluing process looks like this:
- Degreasing surfaces with special primers
- Applying 2 mm double-sided tape (I buy from SDM-chemistry company)
- Applying special glue for gluing
- Gluing the glazing unit and strips
- Drying for 4 days
- Sealing the edge with structural sealant
Important nuance: do not apply double-sided tape right at the edge of the glass. It will either protrude or sink — you will get an ugly edge. My solution: I ask production to glue the tape strip 3 mm deeper from the edge, and seal the 2 mm gap between the profile and glass with structural sealant at the edge. This creates a very nice commercial appearance
Cost of Structural Glazing
Structural glazing is approximately twice as expensive as regular glazing. If a project with classic glazing costs 64 000 dollars, structural glazing may cost 127 000 dollars.
The difference depends on the ratio of fixed and opening glazing:
- With a large amount of fixed glazing, the difference is about 30%
- With a significant amount of opening elements, the cost increases even more
For example, four glass strips measuring 50×2000 mm for one window in painted form can cost 1 300 dollars.
What Drives the High Cost
Materials: structural glazing units are 50% more expensive than regular ones. Glazing units with tooth and painted strips require production on automatic lines.
Production: high precision is required, special templates for positioning embedded elements, manual work. Gluing takes significant time (4 days for drying), requires special consumables and careful packaging.
Installation: highly qualified specialists are required, perfect level installation in all planes, use of special sealants. Sash adjustment is significantly more complex than with regular glazing — it is impossible to correct geometry through the glazing unit.
Alternatives: Semi-Structural Glazing and Carbon Glass
Semi-Structural Glazing
Semi-structural glazing is a compromise between aesthetics and cost. Glazing units are fixed with pressure plates on two sides, while the other two are sealed with UV-resistant sealant.
Advantages: standard glazing units can be used instead of expensive structural ones. Externally, the system is practically indistinguishable from structural glazing thanks to the minimal width of pressure plates (no more than 2 cm). The cost is significantly lower than structural while maintaining the main aesthetic advantages.
Carbon Glass
Innovative technology from Thermoglass company. Instead of aluminum, special spacer frames made of fiberglass with carbon fibers are installed between the glasses. Special sealant and carbon frames provide high rigidity of the edge zone of the glazing unit.
This allows eliminating the aluminum profile and placing glazing units directly next to each other. The glazing unit itself absorbs wind loads and has sufficient rigidity. Based on this technology, a sliding system on a magnetic cushion has been created — the only way to make structural sliding.
Glazing units with carbon frames are quite expensive, but provide 30% better heat-saving characteristics and maximum panoramic view.
Conclusions and Recommendations
Structural glazing is a high-tech solution for creating modern architectural objects with unique aesthetics. From the outside, the building looks like a single glass surface without visible profiles.
Key success factors:
- Quality design taking into account all nuances
- Use of structural glazing units and proven sealants
- Involvement of qualified specialists at all stages
- Perfect level installation in all planes
- Thorough quality control
When to choose structural glazing:
- Projects of prestigious buildings where aesthetics is a priority
- Objects with high requirements for panoramic view
- Buildings in high-tech and modern architecture style
- Projects with sufficient budget (cost is 2 times higher than regular glazing)
When to consider alternatives:
- With a limited budget — semi-structural glazing
- For maximum panoramic view and innovative solutions — carbon glass
- If you need structural sliding — Thermoglass system on magnetic cushion
Structural glazing requires the highest qualification of all specialists — from designers to installers. Any deviations at the production or installation stage can lead to problems that cannot be corrected without complete redoing. But with proper implementation, the result is impressive — a building with a glass facade looks really bombastic.
If you have questions about structural glazing or are planning to implement such a project, contact me! I will select the optimal solution for your object taking into account all technical nuances and budget.
