There are buildings that literally dissolve into the surrounding space. You approach — and you don’t see a structure, but a reflection: trees, sky, neighboring facades. The building itself seems absent. This is not a trick or optical illusion — it is the result of properly executed structural glazing.
Structural glazing is experiencing steady growth today. Twenty-five years ago, this technology was used on small facades; today, it is used to construct large commercial buildings, public facilities, and increasingly — private homes. Architects use it where the goal is not to draw attention to the building but to blend it into the environment. Or where maximum panoramic views are required, without horizontal and vertical shadows from pressure plates.
Let us examine what structural glazing is from a structural standpoint, why it works the way it does, which materials are used and why alternatives are not suitable, and provide a step-by-step breakdown of bonding one structural insulated glass unit — from opening preparation to the final exterior seal.
Structural Glazing: Aesthetics and Engineering
What is Structural Glazing and How It Differs from Standard Curtain Walls
A standard commercial curtain wall is easy to recognize: a pressure plate and decorative cover that protrudes 20–30 mm from the glass plane. Horizontal and vertical lines divide the facade into a grid.
Structural glazing is a fundamentally different solution. The glass infill is not held mechanically on the facade by pressure elements. Instead, the IGU (Insulated Glass Unit) or glass is bonded to the load-bearing structure using a specialized adhesive sealant. The joint between adjacent IGUs is also filled with silicone sealant. No protruding plates, no relief — only a single glass plane with thin silicone joints.
This defines the essence of the construction: the adhesive joint is the primary load-bearing element. It absorbs wind loads, the self-weight of the IGU (if no additional mechanical supports are provided), and thermal deformations — expansion and contraction of aluminum, glass, and sealant under temperature fluctuations.
This is the first and most important attribute of structural glazing, from which all requirements for materials and technology derive.
Architectural Effect: The Building That Disappears
When the architect’s task is to integrate a contemporary structure into a historic environment or natural landscape, structural glazing becomes one of the few tools that can truly achieve this.
One project I had the opportunity to observe — a small building adjacent to a museum complex, surrounded by trees and historic structures. All four facades are fully glazed, two open passages, the structure is almost transparent. The architect’s goal was precisely this: the object must dissolve. Not to compete for attention alongside architectural monuments, but to reflect the surrounding space — birch trees, forest, neighboring buildings.
The result: as you approach the building, you see mostly reflections. The object seems not to exist. That was exactly the intent.
At the same time, the building is all-glass on four sides — meaning a significant amount of solar heat enters the interior. The solution is a multifunctional glass with the appropriate solar heat gain coefficient: protection against overheating while maintaining transparency. This is a standard engineering problem solved at the IGU selection stage.
Advantages of Structural Glazing: Not Just Aesthetics
Beyond appearance, structural facades offer several real performance advantages.
First, better weather resistance. In a standard curtain wall, there is a gap between the glass and the pressure plate where moisture, dirt, and debris accumulate. In a structural facade, everything is sealed with silicone — no places for water to collect and initiate deterioration.
Second, improved acoustic performance. The absence of gaps and joints around the perimeter reduces sound penetration.
Third, easier maintenance. A smooth facade surface without protruding elements does not trap dirt and snow, and is easier to clean. This is especially important for roof structures and sloped facades — water and snow run off without obstruction.
Structural Theory: How It Works from the Inside
Three Different Silicones in One Detail
This is the point often missed even by specialists working with standard curtain wall systems. Structural glazing uses not one but three fundamentally different sealants — and they cannot be confused or substituted for one another.
First — IGU secondary seal. This is the secondary seal of the IGU, made of silicone. In standard IGUs, polysulfide or polyurethane is more common. In structural glazing, only silicone is used, because this joint will be exposed to UV radiation, and only silicone provides the necessary UV resistance throughout the entire service life.
Second — structural adhesive sealant. This is the primary load-bearing element of the entire structure. It bonds the IGU to the load-bearing frame. High adhesion, high strength, high UV resistance, and a wide operating temperature range — from arctic cold to facade overheating above 100°C.
Third — weather-resistant joint sealant. This fills the joints between adjacent IGUs on the exterior. It is not an adhesive — it does not carry structural load. Its task is to seal the joint and withstand all environmental loads: precipitation, UV, temperature cycles.
These three sealants cannot be bought at a hardware store. They are specialized industrial materials selected for a specific project, for specific substrate materials, and are only used after compatibility testing.
Why Only Silicone
UV radiation is the key factor explaining the material choice. In structural glazing, the outer glass is transparent and uncovered at the edge. Sunlight passes through it and directly hits the structural joint and the IGU secondary seal. Neither polysulfide nor polyurethane can withstand this over the long term.
Silicone is fundamentally more resistant to UV than any other sealant. That is its main advantage. Plus, high elasticity allows the joint to «work» under thermal deformations without tearing. Plus, a wide operating temperature range. Therefore, in structural glazing — only silicone, no alternatives.
What Is Visible Through Transparent Glass from the Outside
One nuance to understand before starting the design: the internal construction of the IGU is visible through the transparent outer glass.
The spacer bar is visible. If it is aluminum and not perfectly black, it stands out. The primary seal (butyl) and secondary seal (silicone) are visible — they have different shades of black and may appear uneven. The setting block tape that ensures the correct joint thickness is also visible. If soft-coated glass is used, the perimeter coating removal area may also be visible.
That is why, when designing structural facades, it is strongly recommended to produce mock-ups and view them under actual conditions before full production begins. The choice of black spacer bars, application of enamel around the glass perimeter during tempering, and proper glass selection — all of this is decided in advance and affects the final appearance of the facade.
Variants of Structural Solutions
Structural glazing is not a single scheme but a family of solutions.
The most basic: the IGU is bonded directly to the load-bearing aluminum frame, with no additional mechanical fixings. The adhesive joint carries all loads — wind, weight of the IGU. This is called a non-supported structure.
The variant with mechanical support: special shims or brackets support the weight of the IGU, while the adhesive joint carries only wind load and thermal deformations. The load is distributed, reducing requirements on the joint.
The variant with point mechanical fixings: in addition to adhesive, several point brackets are placed around the perimeter, nearly invisible. Used where building codes require backup — for example, on tall buildings. These brackets slightly disrupt the uniformity of the facade but provide additional safety in case the adhesive joint fails.
Calculation of the Structural Joint
The dimensions of the structural joint are not a matter of preference or experience. They are a calculated value determined by several parameters: wind load for the specific region and building height, self-weight of the IGU, thermal deformations of all structural elements (aluminum, glass, and sealant expand differently), and climatic loads on the IGU itself — lensing effects due to temperature and pressure differentials.
For each project, the silicone sealant manufacturer performs the calculation and issues a written report with the specific joint dimensions. This document establishes responsibility. Self-calculation is technically possible — online calculators exist — but it is better to delegate key decisions to the manufacturer’s specialists.
Important to know: there are forbidden zones for IGU dimensions. Very small units where one side is significantly shorter than the other create increased stress on the joint. Very large units require increased structural bite depth. Exceeding acceptable limits is only possible by modifying joint parameters, verified by calculation.
One-Component and Two-Component Sealants: When to Use Which
Structural adhesive sealants come in two types.
Two-component — base component and catalyst are mixed directly during application through a special extrusion gun. Open time is about 20 minutes, initial vulcanization takes several hours. Used in factories and organized job sites with specialized equipment. Allows fast work and large volumes.
One-component — sold in sausages, applied with a standard caulking gun. More accessible, requires no special equipment. But has a fundamental limitation: curing occurs due to moisture in the air, and moisture does not penetrate to large depths. Maximum sealant depth in a single pass is strictly limited. Full cure time ranges from 7 to 27 days. One-component sealant is used for weather-resistant joints between IGUs directly on site.
Bonding a Structural IGU: Step-by-Step Breakdown
Now let us move from theory to practice. We will go through the step-by-step technology of bonding a structural IGU into a timber frame opening — as performed on an actual project. This is a timber-framed house with heated IGUs for panoramic glazing, but the general technology applies to any type of opening with appropriate primer adjustments.
Step 1: Surface Preparation — Priming
This is the most important stage, determining the longevity of the entire structure. Adhesive sealant does not forgive dusty, greasy, or unprimed surfaces.
Two different primers are used: one for the IGU, another for the opening material. Wood is a capillary, highly absorbent material. Without a specialized primer containing resin that forms an adhesive film, a reliable bond cannot be achieved.
The IGU is primed around the entire perimeter of the bonding zone — removing dust, residual oils, and manufacturing contaminants. Then the opening is primed: sides, top, bottom. The bottom of the opening requires special attention — construction dirt accumulates there. The primer dries quickly and creates an adhesive film ready for adhesive application.
Now let us move from theory to practice. We will go through the step-by-step technology of bonding a structural IGU into a timber frame opening — as performed on an actual project. This is a timber-framed house with heated IGUs for panoramic glazing, but the general technology applies to any type of opening with appropriate primer adjustments.
Step 2: Installing the Backing Rod
Before the IGU is placed into the opening, a backing rod is installed around the perimeter. It serves two functions.
First, it creates the correct joint geometry. The distance from the glass edge to the opening wall is approximately 10–11 mm. The ratio of joint width to sealant depth should be 2:1 — with a width of 10 mm, depth is 5–6 mm maximum. The backing rod establishes the required depth, preventing excess sealant use and ensuring proper joint geometry.
Second, it allows the joint to function under deformations. The sealant must have room to compress and expand — the backing rod provides the necessary space.
The backing rod is pressed in with a blunt tool — never a sharp one, to avoid damaging its structure. Installed around the entire perimeter, evenly, to the calculated depth.
Step 3: Bonding from the Inside — Two-Component Silicone Adhesive
The IGU is placed into the opening. If it is a heated IGU, wires exit from the bottom and top — care must be taken not to pinch them.
For bonding, a two-component, UV-resistant, neutral-cure silicone adhesive is used. Component A (silicone paste) and Component B (catalyst) are mixed in a 10:1 ratio through a static mixer attached to a pneumatic gun.
Before starting, a mandatory test extrusion without the mixer is performed to ensure both components flow evenly. Then the mixer is attached, a test bead is extruded, and homogeneity is checked: the mixed adhesive must be absolutely uniform, without white streaks.
Open time of the adhesive is approximately 20–25 minutes (depends on air temperature). This is the time during which the joint can be tooled.
The adhesive is applied from the inside into the gap between the IGU and the opening wall, evenly filling the entire cavity. The compound is thick, paste-like — it does not sag when applied vertically.
After application, the joint is smoothed with a special spatula dipped in smoothing liquid. The result is a flat, clean joint. Excess adhesive remaining on the spatula is returned to the joint.
Step 4: Curing and Rotation
After bonding from the inside, allow curing. Initial vulcanization of the two-component adhesive takes several hours. Do not rush into subsequent operations.
Step 5: Exterior Sealing — One-Component Sealant
The final step is sealing the exterior joint. This is not an adhesive, but a one-component, weather-resistant silicone sealant specifically formulated for open exposure: direct UV, rain, temperature cycles.
Painter’s tape is applied along the edges of the IGU and the opening to keep the joint clean.
The sealant is applied using a standard gun with a cut nozzle. Skin formation time is about 30 minutes, allowing comfortable work even in direct sunlight and enabling uniform, long joints.
After application, tooling is performed using the same method: a spatula dipped in smoothing liquid. The painter’s tape is removed immediately after tooling, while the sealant is still fresh — otherwise the tape will leave a mark on the joint.
The finished joint serves a protective function: it seals the gap between the IGU and the opening against moisture, UV, and temperature effects. Even if the joint is not visually perfect — in this construction it will be covered by a decorative U-shaped cover.
A Few Words About IGU Replacement
This is an important point that must be honestly stated: replacing a damaged structural IGU is a complex and expensive operation. From the outside, the IGU cut out, a new one is inserted, secured with clamps for a month or two to allow full adhesive cure, then the clamps are removed.
For this reason, structural glazing is not recommended for residential homes where occupants might accidentally damage the IGU. For commercial projects, public buildings, facades with professional maintenance — it is a fully viable solution. For a private residence, it is a question to discuss with the architect before making a decision.
Summary: When to Choose Structural Glazing
Structural glazing is a tool with a clearly defined application niche.
Choose it when the goal is to create a maximally uniform glass facade without visible frames and pressure plates. When the building should reflect its surroundings rather than stand out. When ease of maintenance and long-term durability without dirt accumulation in joints are important.
Do not choose it where replacement of a single IGU must be a simple operation, or where access to a qualified contractor who understands the technology is not available.
The most important thing to remember: structural glazing is not a simplification of a curtain wall system — it is a complication. Three types of silicone, calculation of every joint, compatibility testing of materials, precise adherence to priming and application procedures — all of this requires competence that most standard installation crews lack. The right contractor for such a project is not someone who «also knows how to work with curtain walls,» but someone who has executed structural facades before and understands why each step in the technology is exactly as it is.
