Unitized vs Stick-Built Curtain Walls: Assembly and Interfaces

The main difference is where the system is assembled

Designing Buildings’ curtain-wall overview describes stick systems as installed piece by piece on site, with glazing inserted from inside or outside according to access conditions. It describes unitized systems as prefabricated modules delivered in panels. Both are ways of assembling a curtain wall.

Kawneer’s curtain-wall range makes the distinction explicit for its products: stick-build systems are assembled and glazed in the field; unitized systems are assembled and glazed in the shop. That is a useful manufacturer example of the work being relocated, rather than proof that every product uses exactly the same arrangement.

A curtain wall remains an enclosure with loads to transfer to the primary structure. Larger delivered modules do not eliminate that load path, and a frame assembled on site is still an engineered system. When comparing proposals, record the actual product, configuration and assembly description before making a judgment from a facade photograph.

You may see the spelling “unitised” in British sources. In this comparison it refers to the same assembly concept as “unitized.” Product names can add other terms; use the documents to establish what arrives at the site and what remains to be completed there.

Read the two conceptual activity sequences

The original diagram groups the activities to show where assembly shifts. A real programme can overlap activities and divide the facade into zones. The order, connection details and installation procedure come from the actual system and project.

Download the workflow diagram as SVG.

In the stick-built column, members are assembled into the frame at the site and the infill is fitted there. That makes site access and the conditions under which those operations are performed relevant to the comparison. “Inside glazed” and “outside glazed” describe access arrangements that must be checked for the actual system.

In the unitized column, more assembly and commonly glazing occur before the module reaches the building. Delivery and placing the module become prominent parts of the site plan. The module still has to connect to the structure and adjacent modules or construction through its designed interfaces.

The final box appears in both columns deliberately. Factory assembly changes the division of work; it does not make the site interfaces disappear. Read the accompanying table when you need a text version of that comparison.

Compare the interfaces that remain to be resolved

Do not read “joint” as a single visible line of sealant. Designing Buildings describes curtain-wall functions that include load transfer, thermal control, water resistance, differential movement, and fire, smoke and acoustic separation at interfaces. A useful review follows the referenced detail and asks which function each part serves.

A generic diagram cannot establish whether a particular floor-edge assembly, connection or seal complies with project requirements. Record the detail reference and what remains to be checked instead of treating a simplified sketch as the missing specification.

Factory work and site work need different checks

Off-site assembly can provide a controlled environment for repetitive operations. Designing Buildings identifies factory manufacturing and quality control as benefits that unitized systems can exploit. The practical question is which operations the proposed module actually includes and how those operations are documented and checked.

Site assembly places more frame and glazing work at the building. The comparison should consider access, coordination, the planned sequence and the conditions for the specified operations. It should also establish what inspections and verification are needed, rather than assuming “stick-built” means uncontrolled work.

For a unitized proposal, ask what is checked before dispatch, what may need attention after transport and handling, and which interfaces are completed or verified at the building. A factory-completed element can still be affected by what happens later. For a stick-built proposal, ask how field assembly and the interfaces to adjacent construction are coordinated and verified.

These are questions to obtain from the system and project documentation. They are not claims that either assembly label guarantees quality or that a particular supplier’s delivered module has been independently audited.

Compare the whole programme, not only time at the facade

Unitized assembly can reduce the amount of assembly work performed at the building, but a useful programme comparison includes the work before delivery. Record the design and coordination needed to define the modules, the production and delivery plan, and the site activities that remain.

The size and completeness of what arrives also change the logistics questions. Ask about transport constraints, storage, handling, access and the available work area. Avoid guessing a universal module size or lifting method from the category name; those are properties of the proposed configuration and project.

For stick-built work, establish how members and infill arrive, where they can be handled or stored, and how frame assembly and glazing are coordinated with other work. Smaller components do not remove logistics constraints; they create a different pattern of deliveries and site operations.

Kawneer’s 2500 UT Unitwall page provides a specific unitized curtain-wall example and describes shop-assembled installation efficiency. Its product options and advertised benefits belong to that system. They do not supply a universal saving in cost or time for an unrelated project.

When the question is cost, compare the full scope of each proposal on the same basis: design and coordination, fabrication, transport, installation, interfaces, verification and the project’s own constraints. A shorter site operation is only one part of that comparison.

Three project scenarios: what would you ask next?

Keep assembly, slab position and glazing description separate

Assembly is one classification. Whether an enclosure is described as curtain wall or window wall is another question, involving its arrangement and system details. Glazing descriptions such as captured framing or structural silicone glazing address another part of the configuration.

The 2500 UT Unitwall example lists captured and structural-silicone-glazed options within a unitized curtain-wall product. That illustrates why a unitized label does not tell you which exterior framing expression every project will use.

Record the terms in separate fields: assembly method, enclosure/system designation and glazing configuration. Use a section and the product details for the slab relationship. Use the glazing details for how infill is retained and expressed. This prevents one useful label from replacing several questions it does not answer.

Keep a record of evidence and unresolved interfaces

Download the editable assembly comparison record. It has fields for the proposed configuration, off-site and site work, logistics, detail references and unresolved questions.

Learning case: repeated facade bays
Assembly proposal: unitized modules
Known: more frame and glazing work is proposed off site
Still needed: delivered module scope and handling plan
Connection / movement interfaces: obtain actual detail references
Air / water / floor-edge interfaces: obtain actual detail references
Whole-programme and cost conclusion: not established by the label

When you return to the record, it should distinguish the source’s description from your project-specific conclusion. That makes it possible to update the comparison when the missing documents arrive.

Three checks before choosing a label or drawing a conclusion

These original exercises test the limits of the available assembly evidence.