How the glass is held
Silicone-bonded (four-sided or two-sided). The glass unit is bonded to an aluminium sub-frame with structural silicone. The frame sits behind the glass, so from outside you see glass and a thin joint. In two-sided systems, two edges are bonded and two are mechanically capped, which is a common compromise.
Point-fixed (spider fittings). Bolts pass through holes in the glass into brackets, usually spider arms carried on a structural backing — fins, a truss or a cable net. The most transparent option and the most demanding to detail.
Either way, the load path that a conventional frame used to provide has to be created deliberately, and it is the design rather than the product that makes it work.
Wind is the design case
Design wind pressure rises with height and is significantly higher at corners and near the top of a building. That number drives:
- glass thickness and treatment — heat-strengthened or toughened, and laminated so a failed pane stays in place
- silicone bite depth or bolt capacity, calculated for the pressure on that zone
- sub-frame and bracket sizing, including the pull-out capacity of the slab edge
Using one specification across a whole elevation over-builds the bottom and under-builds the top. We calculate zone by zone. For tall buildings this becomes the governing constraint — see high-rise buildings.
Water, under pressure
A face-sealed façade depends entirely on its outer sealant line. Over twenty years, some of that line will fail, and when it does there is nothing behind it.
Pressure-equalised design assumes the outer line will leak. The cavity behind is vented so it sits at external pressure — removing the pressure difference that drives water inward — and anything entering is collected and drained back out at each floor. In monsoon conditions this is the difference between a façade that lasts and one being patched from year five.
Movement
Buildings move. Slab edges deflect under live load, frames shorten and sway, and aluminium expands and contracts noticeably across Mumbai’s temperature range.
The façade is therefore hung rather than built in: brackets allow relative movement and stack joints at each floor absorb the vertical component. Glass does not tolerate being asked to take structural movement.
Maintenance
Structural silicone has a service life, not a permanent one, and UV and pollution age it. Access for inspection and eventual re-sealing should be designed in from the start — a façade that cannot be reached is a façade that cannot be maintained.
When standard glazing is the better answer
Often. Standard glazing with expressed mullions is cheaper, faster, more tolerant of tolerance, and much easier to maintain. Structural glazing is worth it where the elevation is doing architectural work — a headquarters frontage, an atrium, a street elevation that is part of the brand. See the façade range for the full comparison.