Dead Load Support & the Silicone Bite Optimization

1THE GLASS NEVER TOUCHES THE FRAME

A floating assembly

In a structurally glazed curtain wall, the insulated glass unit looks like it rests directly on the aluminum frame. It doesn't. Hard glass against hard aluminum would concentrate stress at a single line of contact, turning ordinary thermal movement into a crack risk.

Instead, the dead load of the glass — its own weight, pulled straight down by gravity — is carried through a small, deliberately engineered component: the setting block, seated on a setting chair fixed to the frame.

The glass floats on the frame. It never sits on it.

2WHAT THE SETTING BLOCK ACTUALLY DOES

Three jobs, one component

Carries dead load

Blocks metal contact

Spreads compression

A setting block is a short length of dense elastomer — typically neoprene, EPDM, or silicone — placed at the quarter points of the glass's bottom edge.

Supports the weight of the IGU and transfers it into the setting chair, and from there into the mullion.
Prevents glass-to-metal contact, isolating a brittle material (glass) from a much stiffer one (aluminum).
Distributes the load over a defined bearing area rather than a single edge, reducing peak stress at any one point.

Why it matters: without the setting block, the entire dead weight of the IGU would ride on a knife-edge of glass against aluminum — the exact condition that produces edge chips, stress cracks, and eventually seal failure at the corners of the unit.

3WHY THIS DETAIL DRIVES SILICONE BITE SIZE

One load case, not two

The structural silicone joint — the "bite" — is sized to resist wind load: the lateral pressure and suction that tries to pull the glass away from the frame. It is deliberately not sized to carry dead load. That separation of duties is the whole point.

Because the setting block takes the vertical weight of the glass off the sealant's shoulders, the structural silicone bite only has to be engineered for wind — instead of two overlapping load cases. That single-purpose design is what allows the bite dimension to be optimized rather than over-built.

Load case	Carried by	Effect on silicone bite
Dead load (self-weight)	Setting block + setting chair	Removed from sealant design entirely
Wind load (+/−)	Structural silicone	Sized precisely for tensile / shear stress
Thermal movement	Sealant flexibility + joint width	Managed by joint geometry, not bite depth

Without a setting block — sealant resists wind and gravity, forcing a larger bite and wider sightline.

With a setting block — sealant is sized for wind alone; bite follows the minimum tensile / shear requirement.

4HOW THIS FEEDS EFFICIENT OVERALL DESIGN

What a leaner bite buys you

Material efficiency — a smaller, load-appropriate bite means less structural silicone specified per project, a direct cost and material saving at scale.
Slimmer sightlines — because the sealant isn't over-sized to cover a load case it was never meant to carry, frames can be narrower, supporting the slim aesthetic clients want.
Predictable performance — isolating load paths (gravity through blocks, lateral force through sealant) makes the system's behavior easier to model, test, and certify.
Serviceable design — setting blocks are replaceable components. If the glazing needs re-seating or the IGU is swapped, the dead load path can be re-established without disturbing the structural seal.

ENGINEERING TAKEAWAY

Separating dead load and wind load into two dedicated paths — one mechanical (setting block / chair), one adhesive (structural silicone) — lets each component be sized to exactly what it needs to resist. That's the core principle behind lean, efficient curtain wall design.

5QUICK SUMMARY

The IGU never bears directly on the aluminum frame.
Setting blocks on a setting chair carry 100% of the dead load.
This frees the structural silicone bite to be sized for wind load only.
A wind-only bite can be minimized, which reduces sealant volume and sightline width.
The result is a lighter, more material-efficient, and more predictable glazing system.