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

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.