The building is tall and the panels repeat
Factory assembly only pays back over many identical units. The more the facade repeats, the more the tooling and setup cost spreads.
Services / Unitized System
A unitized curtain wall arrives finished.
Panels are assembled and glazed in the factory, then craned into place and locked to the structure floor by floor. The site work becomes installation rather than construction, which is why the schedule tightens and the tolerances hold.
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01
What a unitized system is
The difference from stick is not the material. It is where the wall gets built.
A unitized curtain wall is made of complete panels, usually one floor tall and one module wide. Each one is framed, glazed and sealed before it leaves the factory. The panel arrives at site as a finished object, and nothing is glazed in the air.
Each unit hangs off brackets fixed to the floor slab. Units meet their neighbours at interlocking edges rather than sharing a mullion: two half-mullions come together to form one. So what reads as a single frame on the finished facade is actually the seam between two units.
That seam is the whole engineering problem of the system. It is also why unitized costs more per square metre in material, and less in time on site.
02
The stack joint
Where two units meet is where water, air, and building movement all have to be handled at once.
The horizontal seam where an upper unit meets the one below is the stack joint. It is not sealed shut. It is built as a series of chambers, so the panels can move against each other and still keep weather out.
The outer line of gaskets sheds most of the water. Whatever gets past lands in a drained cavity behind it. That cavity is pressure-equalised, meaning the air pressure inside it matches the pressure outside, so wind has nothing to push the water further in with. The water is then weeped back out to the face.
The joint also has to absorb movement. The building sways, slabs deflect as floors are loaded, and aluminium expands in the sun. A unitized joint takes that up by sliding, which is exactly why it cannot be sealed rigid.
The seam is also where a leak stays. Because the sealing was done in the workshop and not at height, the water that does get in almost always arrives at a unit-to-unit joint, and the work to find it and put it right can be isolated around that one unit. On a stick facade, sealed joint by joint on site, there is no such boundary to work to.
This is the detail we ask about first when reviewing someone else's unitized design. If the joint is drawn as a bead of sealant, the facade will leak.
03
How the work runs
Most of the programme happens before anything reaches the site.
01
Calculation & Value Engineering
Wind load, frame structure, and movement are calculated against the building's height and geometry, then we propose alternatives that cut cost without lowering performance.
02
Shop drawings & approval
Every unit type, joint, bracket, and interface with the structure is drawn and issued for consultant and owner review. Unitized front-loads this: the design is frozen earlier than on a stick job.
03
Bracket survey & setting out
Slab edges are surveyed as built, not as drawn, and brackets are set to that survey. Units are made to one dimension, so the structure's tolerance has to be absorbed here.
04
Factory assembly & glazing
Frames are cut and fabricated in AFI's own workshop, then glazed and sealed indoors. Aluminium profiles come from the extrusion producer backing us.
05
Testing, where the building calls for it
Performance Mockup Unit testing is triggered by height and exposure, so not every project goes through it. Where yours does, our team is experienced in running it at accredited laboratories, covering air leakage, water penetration and structural load, before series production runs.
06
Installation & handover
Units are craned or hoisted to each floor and locked to their brackets, working floor by floor. AFI's project team supervises installation and quality control through to handover.
Our core team has spent decades calculating and installing high-rise facades.
04
When unitized is the right call
It is not the better system. It is the better answer to a particular set of conditions.
The site is hard to work from
A tight urban plot, no space for scaffold, or a facade you cannot reach from outside. Unitized installs from inside the floor plate.
The programme is the constraint
Site installation is measured in floors per week rather than square metres per day, and it can start while the structure above is still going up.
The tolerance matters
Glazing in a controlled factory is more repeatable than glazing at height in weather. On a facade where sightlines are unforgiving, that shows.
Where the facade varies from bay to bay, where the design is still moving, or on a mid-rise where the repetition never accumulates, stick is usually both cheaper and more forgiving. We calculate both when a project sits on the boundary.
05
Questions we get asked
Most come from contractors and consultants sizing up a system before committing to it.
- What is a unitized curtain wall system?
- It is a curtain wall built from complete factory-made panels, each framed, glazed and sealed before delivery, then hung floor by floor from brackets on the slab. Adjacent units interlock at their edges instead of sharing a mullion. The alternative is a stick system, where individual mullions, transoms and glass are assembled on site.
- What is the difference between unitized and stick curtain wall?
- Where the wall is assembled. Unitized is built in a factory and installed as finished panels; stick is built from loose members at height on site. Unitized generally costs more in material and less in site time, holds tighter tolerances, and needs the design frozen earlier. Stick absorbs late changes and variation far more cheaply.
- What is a stack joint in a unitized curtain wall?
- The horizontal seam where an upper unit meets the one below it. It works as a drained, pressure-equalised chamber rather than a sealed line: outer gaskets shed most water, a cavity behind catches and weeps out the rest, and inner gaskets form the continuous air seal. It also has to slide, so that building movement and thermal expansion do not tear it.
- What is a semi-unitized curtain wall?
- A middle route where the frames are assembled in the factory but the glass is installed on site, or where only some components arrive pre-assembled. It recovers part of unitized's precision and speed at a lower tooling cost, and is worth pricing when a project is not repetitive enough to justify full unitization.
- Is unitized curtain wall more expensive than stick?
- Per square metre of material, usually yes. Per completed project, often not. Unitized moves labour from the site into the factory, shortens the installation programme, and reduces the access equipment and scaffold time a stick facade needs at height. On a tall repetitive building the total frequently lands lower, which is why the comparison has to be run on the whole cost rather than the rate.