Factory-Glazed or Site-Glazed? Planning Large Window Unitisation

1. Define the actual assembly options and decision authority

Describe options precisely: fully factory-glazed frame; factory-glazed sub-units joined on site; unglazed assembled frame with site-installed IGUs; knock-down frame assembled and glazed on site; or mixed strategy by opening mark. Identify which joints, gaskets, sealants, setting blocks, beads, drainage features, hardware and inspections occur in each location. ‘Site glazed’ is not one repeatable process.

Confirm that the exact system manufacturer permits each route at the proposed size, glass build-up, orientation and exposure. Obtain controlled fabrication and glazing instructions, component schedules and warranty/inspection conditions without assuming a catalogue section covers field assembly. Assign design, manufacture, logistics, lifting, temporary works, installation, inspection and release responsibilities in writing.

Set decision timing and hold points. Unitisation affects section/joint design, factory equipment, packaging, container/rack layout, erection plant, façade access and programme. A late logistics preference cannot override engineering or silently move factory quality tasks to an unprepared site team.

2. Build the mass, support and system-design baseline

Create an engineer- and manufacturer-reviewed model for every handling state: bare frame, individual lite/IGU, factory-glazed unit, transport rack, lifted assembly and installed unit. Use verified dimensions, component masses and tolerances; calculate mass distribution and centre of gravity for the actual configuration. Include temporary bars, lifting frames, packaging and accessories where they travel with the load. Do not estimate from area alone where frames, laminated glass, hardware or offsets matter.

Map permanent and temporary load paths. Factory-glazed transport can impose racking and vibration conditions unlike installed service; site glazing can expose an unglazed frame to instability or require temporary restraint before glass contributes whatever action the designed system permits. Only the responsible designers may state whether glass participates structurally, whether joints can be site-made, and how the frame remains stable at every stage.

Verify glass processor and system constraints: edge support, setting/blocking concept, orientation, edge protection, contact materials, glazing sequence, drainage, gasket/sealant process and replacement route. These must come from exact approved system and project documents; this guide supplies no dimensions or capacities.

3. Prove the transport, access and lifting route end to end

Survey the route from factory work cell through doors, cranes, rack and container/vehicle envelopes, ports, site gates, laydown, building openings, hoists/scaffolds and final façade position. Use packaged dimensions and swept envelopes, not nominal frame dimensions. Record clearances, rotations, gradients, floor/ground capacity questions, overhead/proximity hazards, weather exposure and rescue/contingency access.

Develop the lifting method through the legally responsible competent party. UK HSE guidance under LOLER says lifting operations involving lifting equipment must be properly planned by a competent person, appropriately supervised and carried out safely; equipment must be suitable, strong/stable and appropriately examined. HSE's planning guidance calls for risks, people, equipment, location, environment, attachment/detachment, overload and continuing integrity to be addressed proportionately.

Do not select vacuum lifters, cranes, slings, spreaders, lifting lugs or frame attachment from load mass alone. Surface condition, glass build-up, pad layout, orientation, redundancy, dynamic effects, radius, wind, temperature, power loss, rated capacities and manufacturer limits matter. A window supplier's lifting sketch is not automatically the contractor's project lift plan.

4. Compare quality risk at the location where work occurs

Factory glazing can offer controlled fixtures, cleanliness, process equipment and inspection, but adds transport mass, large-unit handling and the risk that concealed transit damage or frame distortion reaches site. Site glazing can reduce transport/lift mass per movement and allow replacement sequencing, but transfers cleanliness, weather, access, storage, workmanship, sealant conditions, temporary stability and inspection tasks to the project environment.

Write parallel inspection and test plans. For factory work: component identity, frame geometry, setting/blocking, glass orientation, seals, drainage, operation, cure/hold conditions, packing and pre-dispatch release. For site work: delivered frame and glass identity/condition, storage, opening and support readiness, environmental limits, access, approved sequence, edge protection, process checks, final operation and interface inspection. Preserve hidden-stage evidence before beads, caps or finishes conceal it.

Define damage and nonconformance routes. A chipped edge, rack shift, frame twist, broken IGU, contaminated seal, missing component or out-of-tolerance opening requires containment and authorised disposition. Do not field-adjust, reblock, drill, lift through hardware or substitute a glass build-up merely to keep the crane programme.

5. Run a mark-specific decision and execution gate

Score options only after mandatory constraints are closed. A weighted comparison may consider system permission, structural/temporary design, factory capability, route feasibility, lifting/access resources, environment, quality evidence, programme, replacement and cost—but cannot trade away a failed safety or engineering gate. Record assumptions and sensitivity; one strategy need not cover every opening.

Release each mark group with approved drawings and BOM, handling-state masses/CoG, system glazing instructions, factory/site ITP, packaging and transport design, route survey, competent lift plan, temporary-works and permanent-interface design, labour/competence, weather limits, emergency/contingency plan and responsibility matrix. Verify plant and site readiness before dispatch, not when the truck arrives.

At execution, use identified units and controlled hold points: factory release, rack/load release, site receipt, pre-lift briefing and checks, opening/support readiness, placement and temporary restraint, permanent fixing, glazing where applicable, cure/closure, operation/interface inspection and as-built handover. A successful lift is not evidence that permanent installation or product performance is approved.

FAQ

Continue the project review

Connect this guide with the proposed window and door systems, then review how Cavorlen approaches manufacturing and quality control. When your schedule is ready, send it through the project review form.

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