# Stick System Glazing: Curtain Walling Built Piece by Piece

> Stick system glazing is a curtain wall assembled on site from individual components: vertical mullions fixed back to the structure, horizontal transoms between them, and glass or panel infill installed into the resulting grid. It is the traditional and most flexible form of curtain walling, well suited to low and medium rise and to irregular geometry.

## 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.

## Frequently asked questions

### 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.

## Sources

- [IS 875 (Part 3)](https://standards.bis.gov.in/website/published-standards/department-wise) — Wind loads on buildings and structures
- [EN 13830](https://standards.cencenelec.eu/ords/f?p=CEN:105) — Curtain walling — product standard
- [ASTM E331](https://www.astm.org/products-services/standards-and-publications.html) — Water penetration of exterior windows and curtain walls

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Source: https://hagerstone.com/glossary/stick-system-glazing