Fixed Point Glazing (Spider Systems)

Point-fixed glazing — widely known by the spider-arm fittings that characterise it — supports glass not by capturing its edges in a frame, but by bolting it through a small number of discrete points, usually at or near the corners of each pane. Each bolt passes through a hole drilled in toughened laminated glass and connects, through an articulated fitting, to a stainless-steel spider that gathers several panes at a single node and transfers their load to a minimal back-structure of cables, fins, trusses or masts.

Why eliminate the frame?

The whole point of the system is transparency. By removing the continuous mullion-and-transom grid, point-fixing reduces the visible structure to thin stainless arms and slender supports, giving the maximum possible glass-to-structure ratio and the sense of an almost unframed wall of glass. It is the technology behind airport terminals, museum atria, retail flagships and entrance walls where uninterrupted views and a feeling of weightless transparency are the architectural intent.

Point-fixed glazing emerged from the high-tech architecture of the late twentieth century. The pivotal early examples were the suspended glass walls developed by Pilkington (the ‘Planar’ system) in the 1960s–70s, in which glass was bolted and suspended, and the cable-and-spider walls realised at projects such as the Parc de la Villette glasshouses (Serres) in Paris in the 1980s by RFR with Peter Rice, which established the articulated bolt and the slender cable-truss support as a refined engineering language.

Those projects solved the central problem — how to fix glass at a point without cracking it — through the articulated bolt, which lets the glass rotate relative to its support so that wind deflection is not forced as bending stress into the brittle material around the hole. From that innovation grew the whole family of spider-glazing and structural-glass-wall systems now offered by the major façade system houses and specialist structural-glass engineers.

Everything in point-fixed glazing depends on getting load into and out of a hole in a brittle material without breaking it. The connection has three essential features: the hole, the bolt, and the articulation.

Countersunk and cylindrical holes

Holes are drilled and polished in the glass before toughening (glass cannot be drilled after heat treatment). Countersunk (conical) holes give a flush external bolt head for the cleanest appearance; cylindrical holes with a disc fitting clamp the glass between front and back plates. Hole position is critical: holes must be set back from the glass edge by at least about twice the glass thickness and reinforced by the toughening process, and the stress concentration at the hole governs the glass thickness.

Articulated bolts (rotules)

The bolt incorporates an articulated ball joint — a rotule — so the fitting can rotate as the glass deflects under wind. Without articulation, wind bending would be transferred straight into the glass around the hole, where the stress concentration would crack it. The articulation decouples the rotation, so the glass sees mainly in-plane and bearing loads it can tolerate. Bushings of nylon or aluminium line the hole to avoid steel-on-glass contact, and the whole assembly is engineered to accommodate movement and tolerance.

The spider is the cast or machined stainless-steel fitting that gathers the bolted corners of several panes and transfers their combined load to one point on the support structure. Its arms radiate from a central body to reach the bolt at each adjacent pane corner.

Two-, three- and four-arm spiders

A four-arm spider serves the meeting corners of four panes and is the classic detail of a regular glazed grid; three-arm and two-arm spiders handle edges, perimeters and irregular junctions; single-point fittings handle isolated supports. The number of arms follows the geometry of the glazing grid, and the spider body articulates or fixes to the support node behind.

Material and finish

Spiders are almost always austenitic stainless steel (grade 1.4301/304 internally, 1.4401/316 externally or in coastal exposure) for strength, corrosion resistance and the precise, jewel-like finish the exposed fitting demands. They are investment-cast or machined, then polished, satin-brushed or bead-blasted. Because the fitting is fully exposed and close to the eye, its design and finish are an architectural feature in their own right.

Point-fixing only removes the frame from the glass plane; the wind load still has to be carried somewhere. The spiders fix back to a separate support structure, and the choice of that structure is what gives each point-fixed wall its character.

From glass fins to cable nets

The most transparent solution uses glass fins — toughened laminated glass blades set perpendicular to the wall — so that even the structure is glass. Slender steel mullions or tubular masts are the simplest and most robust support. Pre-tensioned cable trusses and bowstring trusses span large heights with minimal visible structure, deflecting more than a rigid frame but recovering elastically. Full cable-net walls (covered separately under Cable Net & Tensile systems) suspend the glass on a pre-stressed grid of cables for the largest, most diaphanous walls of all.

Deflection and movement

Lightweight cable and truss supports deflect far more under wind than a conventional curtain wall — spans of span/50 rather than span/200 are normal — so every bolt fitting must accommodate the resulting movement through its articulation and slotted tolerance, and the glass must be designed for the deflected geometry. This interaction between flexible structure and brittle glass is the central engineering challenge of the system.

Glass selection for point-fixing is uncompromising: it must be both strong enough to carry concentrated bolt loads and safe enough to remain in place if a pane breaks at height over occupied space.

Toughened laminated glass

Panes are toughened (to develop the surface compression needed to resist the bolt-hole stress concentration) and laminated (so that if one ply breaks, the other and the interlayer retain the pane on its fittings). Typical assemblies are 10+10 mm or 12+12 mm toughened laminated for single glazing, and toughened-laminated IGUs where insulation is required. Ionoplast (stiff) interlayers are often specified so the laminate retains residual stiffness and stays on its bolts after breakage.

Heat-soaking and reinforcement

Because a spontaneous nickel-sulphide fracture in a bolted overhead or high-level pane would be doubly dangerous, toughened glass for point-fixing is heat-soak tested (EN 14179) to weed out NiS-prone panes in the factory. The glass around each hole is the most highly stressed region, and the design is checked by finite-element analysis of the hole, the bearing and the global deflected shape.

Point-fixed glazing achieves its transparency by accepting some performance trade-offs against a conventional framed curtain wall, all of which must be engineered deliberately.

Weather sealing

With no frame, the joints between panes are sealed with structural and weather silicone rather than gaskets in a pressure-equalised pocket. The silicone joint is the entire weather line, so its design, width and workmanship are critical, and movement at the joints (driven by the flexible structure) must stay within the silicone’s capability. Single-glazed point-fixed walls are inherently less weathertight and less insulating than framed IGU systems and are often used for unheated or buffer spaces.

Thermal and acoustic

Single-glazed spider walls offer little thermal or acoustic performance and are used where transparency outranks energy — entrance lobbies, atria, canopies. Where insulation is required, point-fixed IGUs are used, but the bolt penetrations are thermal bridges and the silicone joints limit acoustic performance, so the achievable U-value and Rw are modest compared with a well-sealed framed curtain wall. The specification therefore balances the architectural ambition for transparency against realistic environmental performance.

Point-fixed glazing is a structural-glass discipline, designed by specialist façade and structural engineers rather than selected from a catalogue. The glass is a structural element carrying concentrated loads, and its brittle, no-yield behaviour demands conservative, fail-safe design.

Analysis and safety

Design combines finite-element analysis of the local hole and bearing stresses with global analysis of the flexible support structure and the deflected glass geometry. Glass design follows EN 16612 and the structural-glass guidance of CEN/TC 250/SC11 (the prEN 19100 structural-glass Eurocode in preparation), with robustness checks for the loss of a pane or a fitting. Safety factors on glass are high because of its brittle failure and statistical strength scatter.

Testing and mock-ups

Projects are proven by performance mock-ups tested for air, water, wind and movement, and by load and (often) post-breakage tests on the bolted connection and the glass-and-fitting assembly. Because the system is bespoke, this testing is project-specific rather than a one-off system type-test.

Fabrication is precision work: holes are drilled and polished and edges worked before toughening and heat-soaking, fittings are machined and finished to tight tolerance, and the support structure (fins, cables, trusses) is fabricated and, for cable systems, pre-tensioned to a specified force.

Installation sequence

The support structure is erected and aligned first; cable structures are tensioned to their design pre-load. Panes are then offered up and bolted to the spiders, with careful control of bolt torque, bushing seating and tolerance take-up so that no pane is forced or pinched. Finally the silicone weather joints are applied under controlled conditions. The work is exacting and slow compared with framed glazing, and is carried out by specialist installers.

Point-fixed glazing is chosen where transparency is the headline architectural requirement and the budget and engineering effort can support it.

Its natural homes are airport terminals and transport hubs, museum and gallery atria, retail flagship storefronts, hotel and office entrance walls and lobbies, glazed canopies and links, and feature staircases and balustrades. It is also used for internal glass walls where minimal structure is wanted. It is rarely the right choice for repetitive commercial floors, where a framed curtain wall is cheaper, more weathertight and better insulated — point-fixing is a feature technology, deployed where its drama earns its cost.

Point-fixed glazing sits at the intersection of the glass, structural and façade standard frameworks, and because the systems are bespoke it relies more on engineered design and project testing than on a single harmonised product standard.

Glass, structural and weather

Glass follows EN 12150 (toughened), EN 14179 (heat-soaked toughened), EN ISO 12543 (laminated) and EN 16612 (glass design), with the emerging structural-glass Eurocode work of CEN/TC 250/SC11. Structural design of steel and stainless supports follows the Eurocode 3 family (EN 1993, with EN 1993-1-4 for stainless and EN 1993-1-11 for tension components / cables). Weather performance is verified by project mock-up testing to the EN 12152/12154/12179 family and the CWCT Standard. Drilled-glass point fittings and the assemblies are covered by ETAG/EAD assessment routes where a CE/UKCA marked kit is used.

A point-fixed wall is materially lean in structure but glass-heavy, and its sustainability profile reflects that balance.

The minimal stainless and steel support uses relatively little metal, and stainless is highly durable and recyclable. The thick toughened-laminated glass, however, carries significant embodied energy, and single glazing offers no operational energy benefit, so a point-fixed wall is justified on architectural rather than energy grounds and should be sized accordingly. Stainless fittings have a very long service life and are demountable, and the glass can in principle be removed and recycled; the structural-silicone joints are the main barrier to clean separation at end of life, as in all bonded glazing.

Point-fixed glazing is delivered through three overlapping sources: makers of the spider fittings and bolts, façade system houses offering point-fixed ranges, and — most importantly — specialist structural-glass engineers who design and deliver the bespoke walls.

Fittings & system suppliers

• Pilkington (NSG) — Planar St Helens, UK — bolted / suspended glass assemblies
• SADEV Saint-Vulbas, France — spider fittings & point-fixing hardware
• Schüco Bielefeld, Germany — point-fixed & structural glazing
• SISTEM (Sistem Alüminyum) Çerkezköy, Türkiye — spider & point-fixed systems
• MERO-TSK Würzburg, Germany — space frames & glass support structures
• Çuhadaroğlu Istanbul, Türkiye — point-fixed & structural glazing

Structural-glass engineers and contractors

The defining point-fixed walls are engineered by specialist structural-glass practices and façade contractors — among them RFR, Eckersley O’Callaghan, Dewhurst Macfarlane, schlaich bergermann partner, seele, Permasteelisa and Octatube — who design the glass, fittings and (often cable or truss) support structure as one coordinated, project-specific system rather than a catalogue product.