How does a stick system differ from unitized?

Where the assembly happens. A stick system arrives as lengths of extrusion and separate infill panels, and is put together on the building. A unitized system arrives as complete factory-glazed panels that are lifted and hooked on. Stick is more flexible and suits irregular or one-off conditions; unitized is faster to install and its sealing is done in controlled factory conditions.

How does a stick curtain wall keep water out?

Generally by being drained and ventilated rather than by trying to be perfectly sealed. The system accepts that some water will pass the outer line, and provides a drainage path within the mullion and transom profiles to collect it and return it to the outside through weep holes, while pressure equalisation reduces the driving force pulling water inward. This is why blocked weep holes are a serious defect rather than a cosmetic one.

Where do stick systems typically fail?

At junctions and at site-applied seals. The extrusions themselves are manufactured to tolerance, but the corners, the transom-to-mullion joints, the interfaces with adjacent construction, and any sealing done at height in poor weather are where defects concentrate. Water ingress in a stick facade is far more often a junction problem than a component problem.

What holds the facade to the building?

Brackets fixing the mullions back to the structure, usually at each floor level, designed to transfer wind load into the building and to carry the facade's weight while allowing movement. Bracket design, fixing type and the condition of the supporting structure are engineering matters determined for each project, and they are among the most important elements in the whole system.

Is a mock-up needed for a stick system?

For any facade of significant size, yes. A performance mock-up tested for air infiltration, water penetration and structural loading proves the design and the workmanship approach before it is repeated across the building. Because stick systems depend more on site workmanship than unitized ones, the mock-up also serves as the agreed quality benchmark for the installation crew.

Stick System Glazing Explained | Hagerstone International

Why it matters on a project

Stick systems remain the most widely used form of curtain walling on low and medium-rise buildings, because they are flexible, need no special lifting equipment, and adapt to geometry that would make unitized panels uneconomic.

Their weakness is the same as their strength: almost everything is done on site, which makes workmanship, sequencing and weather protection central to whether the facade performs.

How it goes together

Component	Role
Mullion	Vertical member, spans between floors, carries wind load to brackets
Transom	Horizontal member between mullions, forms the grid
Brackets	Fix mullions to the structure, transfer load, allow movement
Infill	Glazing units or opaque panels installed into the grid
Gaskets and seals	Weather line, drainage and pressure equalisation
Pressure plates and caps	Clamp the infill and finish the external face

Drained and ventilated, not sealed

The most useful thing to understand about a stick facade is that it is not designed to be watertight at the outer face.

It is designed to manage water — letting the small amount that passes the outer line drain within the profiles and return outside through weep holes, while pressure equalisation reduces the force driving water inward.

This has two practical consequences. Weep holes must never be sealed, painted over or blocked with debris. And a facade showing a little water in the drainage channels is behaving as designed, not failing.

Water penetration performance is demonstrated by test, commonly to ASTM E331, with EN 13830 as the curtain walling product standard.

What is engineered, not selected

Mullion size and spacing, bracket design and fixing, glass thickness and deflection limits all derive from the design wind pressure for the specific building — from IS 875 (Part 3) using the actual site, height and terrain. Corners and upper levels see higher pressures.

None of that transfers from a previous project. It is the facade engineer's output for this building.

Common mistakes

Blocking or sealing weep holes. It converts a drained system into a water trap.
Treating junctions as a detail. Corners and interfaces are where facades leak.
Site sealing in poor conditions. Sealant applied to wet or dirty surfaces does not adhere, and the failure appears in the first heavy monsoon.
Skipping the mock-up. With site-assembled work, the mock-up is also the workmanship benchmark.
Ignoring movement at brackets. The facade and structure move differently; restraint in the wrong place cracks glass or distorts frames.
Transferring a previous project's design. Wind pressure is site-specific.

Standards referenced

Wind loading to IS 875 (Part 3); curtain walling product standard EN 13830; water penetration testing to ASTM E331. Mullion sizing, bracket design, glass thickness and design wind pressure must be confirmed by the project's facade engineer for the specific building.

Stick System Glazing: Curtain Walling Built Piece by Piece

Why it matters on a project

How it goes together

Drained and ventilated, not sealed

What is engineered, not selected

Common mistakes

Standards referenced

Standards referenced

Frequently asked

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