Curtain Walling

Curtain walling is a non-load-bearing facade system that spans between floor slabs or structural frames, creating a continuous glazed or panelled envelope around a commercial building. Unlike a traditional shopfront — which is installed within a single-storey structural opening — a curtain wall can extend across multiple storeys and is designed to resist wind loads, support its own dead weight, accommodate thermal and structural movement, and provide weather exclusion, thermal insulation, and acoustic attenuation for the entire building envelope.

Urban Shopfronts designs and installs aluminium curtain wall systems for a range of commercial applications: multi-storey office buildings, retail developments, mixed-use schemes, hotels, educational buildings, and healthcare facilities. We work with stick-built and unitised curtain wall systems, using profiles from established fabricators whose products are tested and certified to BS EN 13830 — the European standard for curtain walling.

Stick-Built vs Unitised Systems

*Stick-built curtain walling* is assembled on site from individual aluminium mullions (vertical members) and transoms (horizontal members), with glass or panel infills glazed into the grid after the framework is erected. Stick-built systems are versatile, cost-effective for smaller projects, and allow adjustments during installation to accommodate site tolerances. They are the most common curtain wall type for single and two-storey commercial facades.

*Unitised curtain walling* consists of factory-assembled panels — each containing a section of mullion, transom, glazing, and weather seals — that are craned into position and clipped together on site. Unitised systems offer faster on-site installation, higher factory quality control, and better weather sealing, but require greater upfront design investment and are typically specified for larger multi-storey projects where the speed and consistency benefits justify the premium.

Structural Performance

Curtain wall mullions and transoms are structural members that resist wind loads — both positive pressure and negative suction — and transfer these loads to the primary building structure at each floor level or structural bracket point. The mullion section is sized by structural calculation to resist the design wind pressure for the building height, location, and exposure category, calculated in accordance with BS EN 1991-1-4 (Eurocode 1: Wind actions).

Our structural calculations are prepared by a qualified engineer and submitted to the building control body as part of the Building Regulations application. Deflection limits for curtain wall mullions are typically L/200 under design wind load (where L is the span between fixings), although more stringent limits may apply for specific glazing types or for buildings with enhanced serviceability requirements.

Thermal Performance

Curtain wall systems must comply with Building Regulations Part L for non-domestic buildings, achieving overall facade U-values that contribute to the building's target energy performance. Our curtain wall profiles incorporate polyamide thermal breaks within the aluminium mullions and transoms, reducing the frame-zone U-value to between 1.5 and 2.5 W/m²K depending on the profile depth and thermal break width.

Combined with high-performance double-glazed units (typically 1.0 to 1.1 W/m²K centre-pane) and insulated spandrel panels, the overall curtain wall assembly achieves the facade U-values required for compliance with Part L and, where specified, BREEAM or other sustainability assessment targets.

Weather Performance and Testing

Curtain wall systems are tested to BS EN 13830 for air permeability, watertightness, and wind resistance. This standard is specific to curtain walling and differs from BS 6375 (which applies to windows and doors). The test sequence includes static air permeability, watertightness under static and dynamic pressure, and wind resistance under positive and negative pressure.

Our systems are also tested for resistance to water penetration under pulsating air pressure — the "hose test" — which simulates the driving rain conditions encountered on exposed UK building facades. Weather sealing is achieved through a combination of EPDM gaskets, silicone weather seals, and pressure-equalised drainage chambers within the mullion and transom profiles.

Glazing and Infill Options

Curtain wall infill panels can be glazed or opaque. Glazed infills use double-glazed sealed units with performance specifications selected to meet the project's thermal, solar, acoustic, and safety requirements. Spandrel panels — the opaque sections typically located at floor-slab and beam levels — use insulated aluminium composite, enamelled glass, or stone cladding backed by thermal insulation.

Structural glazing — where the glass is bonded to the aluminium frame with structural silicone rather than retained by external pressure plates — creates a flush external appearance with no visible frame on the outside face. Structural glazing requires specific design calculations, silicone compatibility testing, and quality-controlled application, all of which we manage as part of the project.

Fire Compartmentation

Where a curtain wall passes across a fire compartment boundary — typically at each floor slab — fire stopping is required to prevent fire and smoke from spreading through the void between the curtain wall and the floor slab edge. We install tested fire-stop systems using mineral wool and intumescent sealant, certified to achieve the required fire resistance period (typically 60 or 120 minutes) at each compartment junction.