# Unitized Curtain Wall: How It Works and When to Choose It

> A unitized curtain wall is a glazed facade delivered as complete factory-assembled panels — glass already set into its frame — which are lifted into place and locked to the building floor by floor, rather than being built up from separate components on site.

## Why it matters on a facade project

The choice between unitized and stick-built is made early, usually before the
facade contractor is appointed — and it is very hard to reverse. It sets the
programme, the crane strategy, whether the building needs facade scaffolding at
all, and how much of the work happens under factory conditions rather than at
height in monsoon weather.

On a tall building it is often the single biggest determinant of how long the
facade takes.

## How it is specified in practice

| Parameter | Typical position | Why |
| --- | --- | --- |
| Panel size | One floor high, one to two modules wide | Panel spans slab to slab so it can be installed floor by floor |
| Assembly | Complete in factory, glass already glazed | Controlled conditions; no site glazing at height |
| Joint type | Interlocking male/female stack joint | Accommodates building movement and drains water |
| Water management | Pressure-equalised, drained and vented cavity | Manages water that gets past the outer seal rather than trying to seal it out |
| Installation | Crane or monorail hoist, floor by floor | Removes the need for full-height facade scaffolding |
| Site labour | Low, but highly skilled | Setting-out tolerance is unforgiving once panels start stacking |

## Common mistakes

- **Comparing rate per square metre instead of delivered cost.** Unitized looks
  more expensive on a BOQ line. It is often cheaper once scaffolding, site
  labour, rework and programme are counted.
- **Underestimating setting-out tolerance.** Panels interlock, so an error in
  the first row propagates all the way up. The brackets and the slab edge survey
  matter more here than on any other system.
- **Ordering before the mock-up is tested.** Once production starts, a design
  change means re-tooling. Air and water testing to ASTM E283 / E331 on a visual
  mock-up should gate the production release, not follow it.
- **Ignoring crane availability.** A unitized programme assumes lifting capacity
  when the panels arrive. If the crane is committed to structure, the facade
  waits and the whole benefit evaporates.
- **Treating it as a tall-building-only system.** It also suits fast-track
  low-rise work where programme matters more than rate.

## When stick-built is the better answer

Unitized is not automatically superior. Stick-built remains the right choice on
low-rise buildings, on facades with highly irregular geometry where few panels
repeat, on projects where the design is still changing, and where the site has
no crane access. Repetition is what makes unitized economical — without it, the
factory tooling has nothing to amortise against.

## Standards referenced

Wind loading follows **IS 875 (Part 3)**, which sets the design pressure each
panel and its brackets must resist. Air infiltration and water penetration
performance is verified against **ASTM E283** and **ASTM E331** on a visual
mock-up before production release.

## Frequently asked questions

### Is unitized always more expensive than stick-built?

Per square metre of facade, usually yes — factory assembly and heavier framing cost more. But the comparison is misleading if it stops there. Unitized removes most facade scaffolding, cuts site labour sharply and compresses the programme, so on a tall or fast-track building the total delivered cost often lands lower.

### What building height makes unitized worth it?

There is no fixed threshold, but the economics usually turn somewhere around eight to ten storeys. Below that, scaffolding is cheap enough that stick-built wins. Above it, access cost and programme risk climb fast and unitized starts to pay for itself.

### Can unitized panels be repaired after installation?

Individual glass units can be replaced, but it is far harder than on a stick system because the frame is not designed to be dismantled in place. This is why factory quality control and pre-installation mock-up testing matter more on unitized than on any other facade type.

## Sources

- [IS 875 (Part 3)](https://standards.bis.gov.in/website/published-standards/department-wise) — Wind loads on buildings
- [ASTM E283 / E331](https://www.astm.org/products-services/standards-and-publications.html) — Air infiltration and water penetration

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Source: https://hagerstone.com/glossary/unitized-curtain-wall