Site-assembled and factory-fabricated glazing: what changes
Glazing is a major part of a building envelope, influencing daylight, ventilation, thermal efficiency, weather protection, appearance, and the speed of construction. The way glazed elements are produced and installed can affect each of these outcomes, especially on projects with demanding performance targets or restricted access.
Site-assembled glazing is built largely at the project location from individual components. Factory-fabricated glazing is manufactured, assembled, and often partially glazed in controlled workshop conditions before being delivered for installation. Neither approach is automatically suitable for every building; the correct choice depends on the design, programme, geometry, access, labour, and required level of quality control.
For developers, architects, and main contractors, the decision should be made early. It affects structural interfaces, setting-out, procurement, lifting plans, storage areas, testing, and the coordination of cladding and roofing trades. A specialist building envelope contractor can help assess these factors before the facade package is fixed.
How the two glazing methods are made
Site-assembled glazing is commonly associated with stick curtain walling. Vertical mullions and horizontal transoms are delivered as separate lengths, fixed to the building structure, and connected on site. Glass panels, pressure plates, gaskets, insulation components, flashings, and cover caps are then installed progressively.
This method gives installers flexibility. Minor adjustments can often be made as the building develops, which is valuable where structural tolerances, slab edges, or adjacent materials are not completely predictable. It can also suit smaller buildings, phased construction, irregular elevations, and projects where delivery access limits the size of prefabricated units.
Factory-fabricated systems are assembled away from the site, frequently as unitised curtain wall panels or pre-engineered window modules. Frames, glass, seals, insulation, spandrel panels, and sometimes internal finishes are prepared in a production facility. The completed units are transported to the project and fixed to brackets or anchors already attached to the structure.
The factory setting allows repeated operations to be standardised and inspected. However, the system requires accurate design information and careful coordination before production begins. Once units are manufactured, late changes can be expensive, so structural surveys, interface drawings, sample approvals, and design sign-off are particularly important.
Performance, tolerances, and quality control
The building envelope must control air leakage, rain penetration, wind pressure, heat transfer, solar gain, and noise. Both site-built and factory-built systems can achieve strong performance, but their risk profiles differ. Site assembly places greater emphasis on installer skill, weather conditions, sequencing, and the consistency of seals and joints across a large elevation.
Factory production offers a more stable environment for cutting, bonding, glazing, gasket installation, and inspection. Repeated components can be checked against defined tolerances before they leave the facility. This can reduce variation between panels and make it easier to maintain a consistent appearance across a high-rise or large commercial facade.
Factory manufacture does not remove the need for site quality control. Units can be damaged during transport, incorrectly stored, or installed against inaccurate anchors. The connection between the panel and the building must still be sealed and tested. A well-designed prefabricated system can perform poorly if the perimeter interfaces, slab edges, or adjoining cladding are not properly resolved.
Site-assembled glazing can perform to the same specification when it is designed, installed, and tested correctly. It is often easier to accommodate small dimensional variations, but every joint is completed in a less controlled environment. Weather exposure, access restrictions, and interruptions from other trades must therefore be considered in the installation method statement.
Programme, labour, and site logistics
The principal programme advantage of factory fabrication is parallel working. While the structure progresses, glazing units can be produced in a controlled sequence. Once floors or structural zones are ready, installation may advance quickly, reducing the time that the building remains open to weather.
This approach can lower the amount of cutting, assembly, and glazing work carried out at height. It may also reduce site labour and simplify installation on tall buildings, where repetitive panels can be lifted into position using cranes, hoists, or specialist lifting equipment. Earlier enclosure can support internal fit-out and improve protection for following trades.
Site-assembled systems can require more labour on the facade and may progress at a slower rate on large, repetitive elevations. Installation can be affected by wind, rain, temperature, access platforms, and the availability of several trades in the same work zone. Nevertheless, the delivery process is often simpler because components arrive in manageable lengths and can be distributed progressively.
Transport is an important distinction. Factory-built panels occupy more space, need careful packaging, and may require just-in-time deliveries. Storage damage or a delayed lifting operation can affect several installation zones. Site-assembled materials are generally easier to stack and handle, although the number of individual components increases and the site team must manage more operations.
Comparing the main project implications
The best selection depends on the balance between repetition, height, geometry, access, and the required delivery speed. A factory-fabricated system tends to benefit buildings with regular grids and a significant number of similar panels. A site-assembled system may be more adaptable where elevations change frequently or where the building has a modest scale.
| Consideration | Site-assembled glazing | Factory-fabricated glazing |
|---|---|---|
| Production method | Components are assembled at the building | Panels or modules are assembled in a factory |
| Design flexibility | High adaptability during installation | Requires earlier design coordination and approval |
| Site labour | Greater installation activity on site | More work completed before delivery |
| Programme | Can be slower on repetitive elevations | Fast installation once units arrive |
| Quality control | Relies heavily on site conditions and workmanship | Benefits from controlled production and repeatable checks |
| Transport | Smaller components are generally easier to handle | Larger units need careful logistics and lifting plans |
| Best fit | Smaller, varied, phased, or irregular projects | Large, repetitive, high-rise, or fast-track projects |
| Change management | Minor adjustments may be easier | Late alterations can cause remanufacture or delay |
Cost comparisons should include the complete installation package rather than the purchase price of frames and glass alone. Site labour, access equipment, protection, storage, testing, transport, lifting, wastage, design development, and programme effects can alter the overall value. A factory-fabricated solution may have a higher initial manufacturing cost but provide savings through faster enclosure and reduced work at height.
Conversely, a smaller project may not generate enough repetition to justify the factory tooling, transport arrangements, or early procurement commitment associated with unitised glazing. A practical cost plan should compare whole-life delivery risks as well as visible material prices.
Design coordination and architectural complexity
The choice becomes more sensitive when a building includes corners, sloping lines, deep reveals, large openings, balconies, projecting floors, or unusual structural movement. Factory-made systems can accommodate complex geometry, but each variation must be engineered, modelled, manufactured, checked, and transported. The number of unique panels should be controlled wherever possible.
Site assembly may provide greater flexibility for non-standard areas, transitions, and last-minute adjustments. However, curved walls and faceted forms still require detailed setting-out, bespoke profiles, accurate support brackets, and carefully planned glass sizes. Early digital modelling and interface reviews help determine which areas should use standard modules and which need special fabrication.
For projects involving unusual geometry, curved wall cladding design can provide useful context on how the facade build-up, support structure, and material tolerances need to work together. Glazing should be assessed as part of the complete envelope rather than as an isolated package, particularly where curved cladding, roof edges, or rainscreen panels meet the glazed frame.
Mock-ups and performance testing are valuable for both systems. They can confirm visual quality, drainage paths, gasket details, sealant transitions, thermal breaks, and interfaces with adjacent materials. On demanding schemes, a benchmark sample or full-size test bay can identify problems before they are repeated across the building.
Weather, maintenance, and long-term operation
The completed facade must remain reliable after installation, not simply pass an initial inspection. Drainage routes, pressure-equalised cavities, gaskets, sealants, movement joints, and replacement access all need to be considered during design. Factory fabrication can produce consistent components, while site assembly can make certain local repairs or modifications more straightforward.
Maintenance access is especially important for large glazed elevations. Cleaning systems, safe access routes, opening vents, replacement glass, and internal access to hardware should be coordinated with the architectural and mechanical designs. A system that is efficient to install may still create operational problems if failed units cannot be replaced without major disruption.
Weather exposure during construction also affects the choice. Factory-built units can close the building quickly, but temporary protection is still needed around unfinished interfaces. Site-built glazing may remain partially open for longer, making sequencing with internal trades and temporary weathering essential. In both cases, installed areas should be protected from impact, contamination, and damage caused by following works.
Roofing and cladding interfaces deserve particular attention. Parapets, gutters, rooflights, coping, insulation, and facade flashings must connect without gaps or incompatible sealants. Clear responsibility for these junctions prevents duplicated details and omissions; guidance on coordinating roofing trades highlights why shared sequencing and interface control are important on a single envelope package.
Selecting the right approach
The decision should reflect the project’s risk profile rather than follow a standard preference. A specialist contractor can review architectural intent, structural movement, performance requirements, logistics, and procurement constraints before recommending stick, unitised, or a hybrid glazing solution.
Useful points to establish during early design coordination include:
- The number of repeated facade bays and the proportion of bespoke elements
- Required air, water, wind, thermal, acoustic, and solar-control performance
- Available crane, hoist, storage, delivery, and access arrangements
- Structural tolerances, movement allowances, and fixing locations
- The relationship between glazing, roofing, cladding, insulation, and internal finishes
A hybrid approach is often effective. Repetitive elevations may use factory-fabricated units for speed and consistency, while entrances, podiums, corners, plant areas, and irregular sections use site-assembled framing. This can balance manufacturing efficiency with the adaptability needed at complicated interfaces.
Early engagement also supports accurate budgeting and procurement. Material specification, glass selection, thermal modelling, bracket design, sample review, and testing can be coordinated before manufacture. Working with established facade and glazing systems, including solutions from brands such as Technal, Kawneer, and Schüco, can provide a clear technical basis while allowing the package to respond to the building’s specific requirements.
The right solution is the one that can be detailed, manufactured, delivered, installed, tested, and maintained with controlled risk. Bak Cladding Solutions can support developers, architects, main contractors, and property owners with integrated cladding, roofing, and architectural glazing packages, from design consultation through to installation and handover. Contact the team early to review the building envelope and establish a glazing strategy that supports performance, programme, and long-term value.