Unitised vs Stick-Built Curtain Wall: When to Use Each

Curtain wall is one of the most scrutinised elements on any commercial facade. It carries the full wind load, keeps the weather out, and plays a direct role in thermal and acoustic performance. But before you get to any of those details, there is a more fundamental decision: unitised or stick-built?

Both systems achieve the same outcome — a non-loadbearing, weathertight facade hung from the building structure. The difference is how they get there. That difference has real consequences for programme, cost, quality, and risk, and the right answer depends on the project, not on preference.

This guide sets out how each system works, where the performance differences lie, and what drives the decision on Australian projects.

How does a stick-built curtain wall work?

A stick-built curtain wall is assembled on the building, piece by piece. Individual mullions (vertical members) and transoms (horizontal members) are fixed to the structure first. Glazing, spandrel panels, pressure plates, gaskets, and cover caps are then installed in sequence — typically from scaffolding or swing stages.

The framing goes up first. The glass follows. Seals are applied at height, in whatever conditions the site offers that day.

This has been the standard method for decades. It is well understood, widely available, and most facade fabricators in Australia can deliver a stick-built curtain wall without specialist factory setup. For low-to-mid-rise commercial buildings — generally under ten to fifteen storeys — it remains the most common approach.

The strengths are straightforward: lower upfront material cost, simpler logistics (components ship flat, not as assembled panels), and flexibility to accommodate irregular geometries where every bay might be slightly different.

The limitations are equally straightforward. Assembly quality depends on site conditions — wind, rain, dust, temperature, and the skill of the crew working at height. Every gasket joint, every structural silicone bead, every glass setting block is installed in an uncontrolled environment. Defects are harder to detect until the facade is water-tested, and remediation requires access equipment.

How does a unitised curtain wall work?

A unitised curtain wall reverses the sequence. Complete panels — typically one storey high and one structural bay wide — are assembled in a factory. Each unit arrives on site fully framed, glazed, sealed, and quality-checked. A crane lifts the panels into position, and they hook onto brackets pre-fixed at each slab edge. Adjacent panels interlock through male-female gasket joints at mullion and stack-joint locations to form a continuous weathertight envelope.

The factory becomes the assembly line. The site becomes installation only.

This shifts the quality-critical work — gasket seating, structural silicone application, glass setting — into a controlled environment with jigs, repeatable processes, and inspection before dispatch. Units can be water-tested on the ground before they ever leave the factory. Defects are caught and corrected at bench height, not thirty storeys up.

Installation rates reflect the difference. A unitised facade crew can typically install twenty to forty panels per day, compared to five to ten square metres per day for stick-built assembly. On a mid-rise or high-rise project, that speed compounds into programme savings measured in months.

What are the performance differences?

Both systems are tested and assessed under the same Australian standards. AS/NZS 4284:2008 defines the test sequence for curtain wall facades: water penetration resistance (static and cyclic), air infiltration, and structural adequacy at both serviceability and ultimate limit states. Wind actions are determined under AS/NZS 1170.2. There is no separate standard for unitised versus stick-built — performance requirements are the same.

Where the systems diverge is in consistency of installed performance.

Water penetration. Both systems must resist water entry under the pressures specified for the building’s wind region and height. Typical test pressures range from 600 Pa on low-rise buildings to 1,200 Pa or more on high-rise towers. Unitised systems, assembled and sealed in factory conditions, tend to deliver more consistent results across the full facade. Stick-built systems are more sensitive to workmanship variation — a single poorly seated gasket at a mullion-transom intersection can compromise a bay.

Air infiltration. AS/NZS 4284 sets a maximum of 1.5 L/s/m² at 75 Pa. Unitised systems routinely achieve below 1.0 L/s/m² because the critical seals are factory-applied. Stick-built performance is more variable, and achieving consistently low air infiltration across a large facade requires rigorous site quality assurance.

Structural adequacy. Both systems must resist design wind pressures with deflections within the specified serviceability limits — typically span/175 for mullions, though some specifications call for span/200. The structural design process is the same for both. The difference is that unitised systems accommodate building movement (inter-storey drift, thermal movement, structural deflection) through the gasket joints between panels, with typical drift accommodation of fifteen to twenty-five millimetres. Stick-built systems rely on mullion splice joints, which generally offer less movement capacity.

Seismic performance. For buildings in seismic regions, inter-storey drift accommodation is a genuine design consideration. The stack-joint design in unitised systems provides inherent movement capacity that stick-built splice joints do not easily replicate.

When does unitised become more economical?

This is the question most project teams ask first, and the answer is project-specific. But the industry rule of thumb in Australia places the crossover point at roughly 8,000 to 15,000 square metres of facade area, or approximately fifteen to twenty storeys.

Below that range, stick-built is usually cheaper on a total installed cost basis. The material cost per square metre is typically fifteen to thirty per cent lower, and the factory setup, transport of assembled units, and crane time required for unitised installation are not justified by the programme savings.

Above that range, the economics shift. Unitised installation is faster — significantly faster — and on a large project, programme time has a direct cost. Holding costs on a commercial tower can run to $50,000 to $100,000 or more per month. If a unitised facade saves three to six months of programme compared to stick-built, the saving in holding costs alone can exceed the material premium.

There are also indirect savings. Less scaffolding. Fewer trades working on the facade simultaneously. Earlier weather-tightness, which allows internal fit-out to begin sooner. These are harder to quantify at tender stage, but they are real.

The crossover is not just about building height. A ten-storey building with a large, repetitive facade may justify unitised. A twenty-storey building with a complex, highly varied facade may favour stick-built for flexibility. The decision should be made on project-specific analysis, not rules of thumb.

What about quality control?

This is where the distinction is sharpest, and it often gets underweighted in the specification process.

Stick-built assembly happens outdoors, at height, in variable conditions. The workforce changes. Supervision varies. A gasket that seats perfectly in a factory jig may not seat perfectly on a windy scaffold at the fifteenth floor. The result is not necessarily failure — most stick-built curtain walls perform adequately — but the variance in quality across a large facade is wider.

Unitised assembly happens in a factory. The environment is controlled. The processes are repeatable. Units can be inspected, tested, and rejected before they leave the ground. The quality variance is narrower, and the cost of fixing a defect in the factory is a fraction of the cost of fixing it on the building.

Since the 2019 Senate inquiry into non-conforming building products and the subsequent NCC 2022 amendments, the Australian construction industry has placed greater scrutiny on facade testing, documentation, and quality assurance. Factory-assembled systems, with their documented QA processes and pre-dispatch inspection records, align well with this direction.

How does this relate to Valmond & Gibson’s 165CW system?

The 165CW is a unitised curtain wall system designed, engineered, and extruded in Australia. It uses 6060-T6 primary framing alloy with a 165mm internal frame depth, thermally broken glazing adaptors with polyamide strip and aluminium nose cap, and accommodates insulated glass units from 24mm to 40mm. Stack-joint movement capacity is ±25mm, and mullion movement capacity is ±10mm.

It conforms to AS/NZS 1170.0, AS/NZS 1866:1997, AS/NZS 4284:2008, AS 3715:2002, and AS 1231:2000. A dedicated LogiKal by Orgadata database supports estimating, cutting optimisation, AutoCAD export, and CNC machine control for fabrication.

The system has been used on projects including Tweed Valley Hospital (Kingscliff, NSW), Murdoch University (Perth, WA), and the Queanbeyan Civic and Cultural Precinct (NSW) — a range of building types that reflects the versatility of unitised curtain wall when it is specified appropriately.

Being Australian-designed and extruded means shorter lead times than imported systems, the ability to modify profiles without international procurement cycles, and technical support in the same time zone as the project team.

Which system should you specify?

There is no universal answer. The right system depends on building height, facade area, geometry, programme constraints, site access, and budget. Here is a practical framework:

Consider stick-built when:

The building is under ten to fifteen storeys
Facade area is below 8,000 m²
The geometry is highly varied with few repeating bays
Budget is constrained and programme is not the critical path
Regional sites with limited crane access or transport constraints

Consider unitised when:

The building is above fifteen storeys, or facade area exceeds 10,000 m²
Programme speed is critical — particularly on CBD sites
Repetitive facade bays allow factory efficiency
Quality consistency across a large facade is a priority
The project requires seismic drift accommodation or significant building movement tolerance

On projects near the crossover point, both options should be costed and programmed. The cheapest system per square metre is not always the cheapest system for the project.

The bottom line

Unitised and stick-built curtain wall are not competing systems — they are different tools for different situations. Understanding when each one makes sense is part of getting the facade specification right, and getting the facade specification right is how projects avoid cost overruns, programme delays, and performance issues that surface after handover.

Valmond & Gibson supplies the 165CW unitised curtain wall system for projects where factory quality, programme speed, and Australian technical support matter. For projects where stick-built is the better fit, we are happy to say so — the goal is the right system on the right project, not a sale at any cost.

Last updated: 3 April 2026

Unitised vs Stick-Built Curtain Wall: When to Use Each