How Curtain Walls Are Installed: A Step-by-Step Guide

Curtain walling looks like glass. Installation is really about brackets, gaskets, sealants and setting-out. Get any of those wrong and the wall leaks, fails CWCT testing, or holds up the entire programme. Get them right and you have a facade that performs for 40 years.

This guide walks through the actual sequence — the same one Delta Facades follows on every stick and unitised curtain wall package we install across London and the UK. It's aimed at specifiers, project managers and main contractor site teams who want to understand what their facade subcontractor is actually doing on site.

Step 1 — Survey and Setting Out

Before a single bracket is fixed, the primary structure is surveyed. Total-station or laser-scan surveys pick up slab edges, column faces and any deviations from design. On a large concrete or SFS structure, deviations of ±15–25mm from the design line are typical — the curtain wall has to absorb that inside its bracket tolerances.

Setting out then translates the design grid onto the structure. Reference gridlines are marked at every level, deviations are logged against tolerance, and any panels or profiles that need cutting to suit are identified before fabrication is finalised.

Step 2 — Bracket Installation

Bracket installation is where curtain walling is really engineered. Brackets are fixed to the slab edge (or structural steelwork) via cast-in anchors, chemical anchors or through-bolted plates, and they carry the entire weight of the curtain wall plus wind load.

Each bracket is set to design position with three-dimensional adjustment — vertical, horizontal and out-of-plane. Setting is checked against total-station readings before final tightening. Torque and adjustment records go into the golden thread.

Fire Stops and Cavity Barriers

On buildings over 11m residential and 18m general (Building Safety Act higher-risk buildings), horizontal cavity barriers are installed at every compartment floor and vertical barriers at every compartment wall — before the curtain wall goes in front of them. Barrier install is photographed and logged by compartment location for the golden thread.

Step 3a — Stick Curtain Walling Installation

Stick systems are built up on site, piece by piece. The mullions (vertical profiles) go up first, fixed back to the brackets with sliding shear connections that allow inter-storey movement. Transoms (horizontal profiles) span between mullions and are locked into the mullion pockets with cleat-and-screw fixings, always with EPDM gaskets between the profiles.

Insulated glass units (IGUs) and spandrel panels are then loaded into the grid — usually from the inside — sitting on setting blocks with structural glazing gaskets around every edge. External pressure plates screw onto the mullion and transom faces to clamp the IGUs; snap-on capping conceals the fixings. Every sealant joint, gasket compression and drainage slot is inspected before the next bay is closed.

Step 3b — Unitised Curtain Walling Installation

Unitised systems are factory-assembled, pre-glazed panels that arrive on site typically 1.5–4m wide × one floor tall. They're craned into position, one at a time, and locked into the panel below via a male/female stack joint.

The sequence is: hook onto the crane, lift into position, land on the stack joint, engage the mullion-to-mullion split joint with the panel alongside, drop onto the bracket carrier, lock off. A typical crew of four installs 15–25 panels per crane shift on a well-organised site — one storey of a 400–500m² floorplate per crane per week is the target rate on high-rise London and Docklands towers.

Because gaskets, IGUs and seals are all factory-fitted, on-site QC is faster and defect rates are far lower than stick. But bracket setting-out has to be right first time — there's no adjusting a landed panel.

Step 4 — Sealing and Weathertightness

Curtain walls are drained and pressure-equalised systems, not sealed boxes. Water that gets past the outer gasket is captured in the drainage cavity and let out through weep holes at the bottom of each mullion or panel. The system relies on the primary and secondary gaskets being intact and correctly compressed, and on the transom-to-mullion junctions being sealed with the manufacturer's specified silicone.

Every sealant joint is tooled, inspected and photographed. Gasket compression is inspected panel by panel. Weep hole locations are logged.

Step 5 — CWCT Hose Testing

Once installation is complete on an elevation, the wall is tested against CWCT Test Sequence B — the on-site hose test that mimics wind-driven rain. A calibrated spray rig delivers water at 3 l/min/m² across the target area for 15 minutes per bay, while the internal face is monitored for leaks.

Failures — water tracking past the gasket line to the internal face — are fixed on the spot: gasket reset, sealant re-tooled, or on rare occasions a full panel removal and reset. Every test is recorded on drawings and forms part of the O&M pack at handover.

Step 6 — Handover and O&M

At handover the facade subcontractor issues the O&M pack: product certificates, system fire test evidence, CWCT test results, installation photographs, weep hole and cavity barrier location plans, and a maintenance schedule. On higher-risk buildings this all sits inside the golden thread and is available to the Building Safety Regulator.

Common Failure Modes

• —Gasket rollover during panel install — the top gasket edge folds instead of sitting proud, causing local water bypass
• —Missed sealant at transom-to-mullion junctions — the smallest 20mm miss causes visible internal wet patches
• —Bracket over-torqued or under-torqued — over-torque cracks the anchor, under-torque means the connection slips in service
• —Setting blocks omitted or under-sized — the IGU sits on the gasket instead of on hardened rubber, and edge stress cracks the glass
• —Cavity barrier not installed to the barrier line — a small offset lets fire and smoke through the compartment

Frequently Asked Questions