Unitised vs Stick Curtain Wall: Two Evidence Trails

The system choice usually gets made in a cost meeting. Unitised or stick: crane time against scaffold time, factory labour against site labour, a programme that wants the building watertight by a date. Then, months into the install, a question arrives that the cost meeting never priced. The client's building safety consultant wants to know what holds a particular panel on the ninth floor of the east elevation, who fixed it, and what was checked before it was closed in. The answer is in your records somewhere. Where it is depends almost entirely on the decision taken in that first meeting.

What's Actually Being Asked

Nobody regulates the choice between unitised and stick curtain walling. What they look at is the external wall that results, and the information that proves it was built as designed. On a higher-risk building in England, broadly one of at least 18 metres or seven storeys with at least two residential units (and, during design and construction, hospitals and care homes of that height), building work needs building control approval from the Building Safety Regulator before it starts, changes during construction run through a change control process, and the completion certificate application has to be backed by information about what was actually built. That information forms part of the golden thread, which is kept through design and construction and handed over at completion; once the building is occupied, the accountable persons have to keep it accurate and available. Below the threshold the building control route is different, and the underlying question is the same: can you show what is on the wall, and that it matches what was designed, tested and approved?

The two systems answer that question from different places. Briefly, for anyone outside the trade: a stick system is built on site, piece by piece, with mullions fixed to the structure on brackets and transoms fixed between them, then glazing and infill panels installed and sealed in place. A unitised system is assembled and usually glazed in a factory as complete units, each typically a floor high, which are lifted onto brackets at the slab edge and interlock with their neighbours along vertical and horizontal joints. Plenty of jobs sit somewhere between, with panelised or semi-unitised hybrids, and the evidence pattern of a hybrid is a mix of the two below. The building is not asking which you chose. It is asking you to prove the result. But the choice decides where that proof gets made, by whom, and how easily it comes apart.

The Evidence That Answers It

The stick trail: made on the scaffold, over time

On a stick system almost all of the build evidence is generated on site, in sequence, and much of it is covered up by the next operation.

• Setting-out and bracket fixings. Bracket positions against the structural grid, anchor type and embedment, torque or pull-out checks where specified, recorded per bay before the frame goes on.
• Frame assembly. Mullion splices and movement joints, transom connections, and the drainage and pressure-equalisation details that only exist correctly if they are built correctly.
• Glazing and infill. Which glass or panel went into which opening, gasket and seal installation, and setting and location blocks, and any structural bonding the system needs.
• Slab-edge fire-stopping and cavity barriers. Installed and inspected before anything closes them in.
• Site water testing. Hose testing of completed areas to the method set out in the specification, with the location, result and any remedial work recorded.
• Deviations. Every departure from the tested and approved configuration, with its justification.

The unitised trail: split between factory and façade

On a unitised system a large share of the evidence moves to the factory, and what remains on site is concentrated at the joints and the fixings.

• Factory records per unit. The materials, glass, assembly checks and sealing inspections for each unit, recorded against a unit identifier.
• Transit and storage condition. Damage on delivery, protection on site, and any repair carried out before installation.
• Anchors and brackets. Cast-in or post-fixed anchor positions and checks at each slab edge, usually installed well ahead of the units themselves.
• The installation map. Which unit identifier was hung in which position on which elevation and floor, and on what date.
• Joints, perimeter and fire-stopping. Stack and mullion joint sealing, perimeter seals, and the slab-edge fire-stopping line between the units and the structure.
• Site water testing and deviations. As for stick, but focused on the joints and interfaces rather than the whole frame.

In both cases the test evidence for the system itself sits underneath all of this: the specimen that was tested, and every way the building departs from it. That is its own subject, covered in our post on keeping CWCT test evidence findable.

Why the Spreadsheet Version Fails

The two systems break the usual spreadsheet-and-email approach in different ways. On stick, the evidence is real but scattered across time: a bracket inspection sheet in the site cabin, a fire-stopping photo in a WhatsApp group, a hose test result in an email from the supervisor, each describing a location in words that made sense on the day. On unitised, the failure is quieter and harder to recover. The factory may keep a thorough record against unit numbers. The site keeps its own record against elevations and floors. The document that joins them, which unit went where, often lives in an installation tracker spreadsheet maintained by one site engineer, overwritten as units are swapped, damaged or re-sequenced. When that tracker goes, the factory record can be complete and still answer nothing, because nobody can say which record describes the panel on the ninth floor.

Keeping It Provable

The fix is the same principle applied to two different shapes of work: anchor every record to the place on the building it describes, at the moment it is made. For a stick system that means the bracket check, the fire-stopping inspection and the hose test are each captured against elevation, level and grid while the scaffold is still there, so a question about a bay can be answered by going to the bay rather than to an inbox. For a unitised system it means one more step: the unit identifier becomes a recorded link between the factory record and an installed position, captured when the unit is hung rather than reconstructed from the tracker months later. A swapped or replaced unit then changes the record instead of breaking it.

Done that way, the two trails stop being two different filing problems. Both become a record of a building, built as the work happens, that can answer a question about one panel without anyone needing to remember how the job was run.

The Monday Checklist

1. Pick one installed panel or bay on a live job, by elevation and floor, and try to assemble its evidence from records alone: fixings, fire-stopping, water test, and for unitised, its factory record. Note what you cannot find.
2. For unitised work, identify who owns the unit-to-position record today, where it lives, and what happens to it when a unit is swapped or replaced.
3. For stick work, list the inspections that get covered by the next operation, and confirm each one is signed before close-up rather than after.
4. Replace descriptive locations with a fixed reference (elevation, level, grid) across both site and factory records.
5. Agree with the factory how unit identifiers appear on the unit, the delivery note and the installation record, so the same number survives all three.
6. Put every deviation from the tested configuration into one register, with a dated, signed justification against the location it affects.
7. Ask the client now what form they need the façade handover information in, and through them whoever will hold it after completion: on an occupied residential higher-risk building, the accountable person; on other buildings, the owner or operator. Build to that from the first unit or bay.

Where BrieXO Fits

The BrieXO bundle that covers the site end of this work is FIELD, and it is live today: daily site records and ITP sign-offs, governed photo evidence, operative competence records, record-linked communication and programme visibility, captured as the work happens and linked to the location on the building they describe, through the spatial spine every BrieXO tenant runs on. It does not design or test a curtain wall, and it does not decide whether a system or a deviation is acceptable: those are judgements for the competent people making them. Factory production records stay with the factory; the unit identifier you agree with them is what connects those records to the installed position. It supports, and does not certify, compliance. It supports your golden-thread and façade evidence duties; it doesn't discharge them. The façade-specific picture is on our façade contractors page.

Related reading:golden-thread duties by trade, rebuilding a golden thread during cladding remediation, and the as-built record at Gateway 3 handover.

George Sfica is a senior design manager at a specialist façade contractor, with 23 years in manufacturing and construction, eleven of them in façades and external envelopes, spanning fabrication, installation and design management, an MSc in Façade Engineering and an IFE Level 2 Certificate in Passive Fire Protection. He is the founder of BrieXO.