How to Specify Aluminium Curtain Wall Systems for Commercial Buildings

Specifying aluminium curtain wall systems for a UK commercial building requires more than selecting an attractive glazed façade. Architects, contractors, developers and façade consultants need to define structural requirements, thermal performance, weather resistance, glazing safety, fire safety interfaces, installation constraints and long-term maintenance before the system is finalised.

A well-prepared specification translates the building design into measurable performance requirements that a manufacturer and installation team can assess. It also helps reduce uncertainty during procurement, coordination and construction. The most effective approach is to establish the building’s requirements first, assess suitable curtain walling systems against those requirements, and confirm that the proposed solution is supported by appropriate technical information.

1. Establish the Project Requirements Before Selecting a System

The first step in specifying aluminium curtain wall systems in the UK is to document what the façade must achieve within the wider building design.

Curtain walling is generally a non-loadbearing external envelope attached to the building’s structural frame. Although it does not support the primary building structure in the same way as loadbearing walls, it must transfer its own weight and applicable environmental loads safely to the supporting structure.

This makes early coordination essential. A system that suits the visual concept may not automatically suit the building’s dimensions, exposure, intended occupancy or construction programme.

Define the building’s use and operating conditions

An office, retail development, educational facility and hotel may have different requirements for daylight, privacy, acoustic comfort, ventilation and solar control.

Before writing the specification, establish:

• The building’s use, height, orientation and exposure to prevailing weather.
• The approximate façade areas, elevations, grid dimensions and desired sightlines.
• The expected internal temperature and humidity conditions.
• The required levels of daylight, glare control and acoustic separation.
• Whether opening vents, integrated doors or other interfaces are necessary.
• The maintenance strategy and expected design life of the façade.

These details provide the basis for choosing appropriate system components and defining performance criteria.

For example, a glazed office elevation facing south or west may need careful solar-control design to manage glare and solar gains. An exposed elevation on a taller building may require particular attention to wind loading, water penetration and movement.

Neither situation can be addressed reliably by choosing a frame based on appearance alone.

Prepare a project-specific performance brief

The project team should convert its design objectives into requirements that can be checked.

Instead of specifying that the façade must offer excellent weather resistance, establish which performance evidence is required for the building’s exposure and intended use. Instead of requesting high thermal efficiency, identify the relevant thermal metric and the performance target agreed by the design team.

The Centre for Window and Cladding Technology (CWCT) provides a useful framework for considering building-envelope performance, including weathertightness, loading and movement, thermal and moisture performance, acoustics, fire performance, safety and service life. Its specification guidance can help the design team identify relevant performance considerations.

2. Choose a Curtain Walling System That Suits the Project

Once the performance brief is established, assess which curtain wall construction method suits the building’s geometry, procurement arrangements and site conditions.

The two common approaches are stick-built and unitised curtain walling. Their suitability depends on factors such as project size, façade repetition, logistics and the construction programme.

Stick-built aluminium curtain walling

A stick-built system is assembled on site from individual framing components, generally including vertical mullions and horizontal transoms, followed by glazing and associated components.

This approach can offer flexibility when façade dimensions vary or the building contains irregular elevations. It can also suit projects where the site team has the access, labour, sequencing and quality-control arrangements needed for on-site assembly.

The specification should address component delivery, frame assembly, glazing sequence, access equipment, weather protection and inspection requirements.

Unitised curtain walling

Unitised systems use larger factory-assembled façade panels that are transported to site and installed as complete units or modules.

Factory assembly can support repeatable production and may suit projects with extensive repetitive elevations. However, panel dimensions, transport limits, lifting arrangements, site access and installation tolerances must be considered from the outset.

Unitised and stick-built systems should not be treated as interchangeable without considering the specific building and supply arrangements.

Match the construction method to the façade design

A practical assessment should consider the following:

Project consideration	What to establish
Façade geometry	Repetition, curved or angled areas, building height and panel dimensions
Programme	Factory production, site assembly and installation sequence
Site logistics	Storage, delivery access, lifting capacity and working space
Quality control	Inspection procedures and how installed work will be checked
Interfaces	Connections to the structure, adjacent cladding, roofs and windows
Future maintenance	Safe access, cleaning and component replacement

For commercial projects where the design calls for both vertical and sloped glazing, confirm that the proposed system is suitable for the actual application and that its technical documentation covers the required conditions.

Fenetek Ltd’s aluminium curtain walling system page describes the Cortizo TP52 as a stick-built solution with vertical or sloped glazing options, integrated drainage and thermal breaks, and compatibility with vents and doors. These details provide a starting point for discussion, but final suitability must be confirmed against the project’s dimensions, performance requirements and technical documentation.

3. Specify Structural Performance and Movement

Structural coordination is one of the most important parts of curtain wall design. The façade must accommodate the loads imposed on it without compromising its stability, weather resistance or glazing integrity.

The required design depends on the building, its location, the supporting structure and the relevant engineering assessment.

Wind loads, dead loads and fixing arrangements

Wind pressure and suction act on external façades and vary according to factors such as building height, geometry, location and exposure.

The specification and design calculations should establish how these loads pass from the glazing and framing through brackets and anchors into the main building structure.

The following matters need to be coordinated:

• Mullion and transom dimensions and spans.
• Bracket positions and fixing arrangements.
• Supporting substrate strength and condition.
• Applicable design loads and permitted deflections.
• Local requirements around corners, parapets and exposed elevations.
• The relationship between structural calculations and the proposed system configuration.

The façade designer and structural engineer should confirm the design assumptions together. A manufacturer’s standard configuration should not be assumed suitable for every span or building condition.

Allow for movement between the façade and structure

Commercial buildings move during their service life. Sources include temperature changes, wind-induced movement, structural deflection and construction tolerances.

Curtain walling therefore needs suitable movement allowances at its connections and interfaces.

For example, a slab edge may deflect differently from the façade framing attached to it. The fixing arrangement must accommodate the anticipated movement without transferring unintended loads into the glazing or damaging seals.

The specification should clarify design movement requirements, connection details and tolerances. It should also identify which party is responsible for checking the compatibility of the structural design and the curtain wall manufacturer’s system details.

These decisions are better resolved before fabrication than through adjustments on site.

4. Specify Glazing and Thermal Performance Together

The performance of a glazed façade depends on the combined behaviour of the glazing units, aluminium frames, seals, joints, connections and interfaces with the surrounding construction.

A specification should therefore assess the complete proposed façade rather than relying on a single glass or frame figure.

Understand the relevant thermal measurements

Thermal transmittance, expressed as a U-value in watts per square metre kelvin (W/m²K), indicates the rate at which heat passes through a building element under defined conditions. Lower U-values generally indicate lower heat transfer.

However, different U-values describe different elements. Centre-pane glass performance, window performance and whole-façade performance are not necessarily equivalent.

When comparing aluminium curtain wall systems, identify:

• The required thermal performance of the relevant façade element.
• Whether the stated figure applies to the glazing, frame or complete assembly.
• The assumptions and calculation method behind the figure.
• The effect of frame proportions, interfaces and thermal bridging.
• The glazing specification required to achieve the stated result.

A thermally broken aluminium profile incorporates a less conductive separation between sections of the frame to reduce heat transfer through the metal. Its contribution must still be assessed alongside the glass and other façade details.

Select glazing for the building’s use and orientation

The glazing specification should consider more than insulation.

Solar-control glass may help limit solar gains, while appropriate glazing choices can support daylight provision, glare management and visual comfort. Acoustic requirements may also influence the choice of glass thickness, unit construction and interlayer arrangement.

For an office building beside a busy road, the team may need to balance external noise reduction against daylight and solar-control objectives. For a highly glazed reception area, controlling glare and overheating may be especially important.

The final selection should follow the project’s environmental and occupancy requirements.

Confirm glass safety requirements

Glazing type and thickness must be selected for the proposed location, pane dimensions, loading conditions and applicable safety requirements.

The specification should identify relevant requirements for glass strength, impact safety where applicable, edge conditions and the consequences of glass breakage.

Large panes, overhead or sloped glazing, and glass near accessible areas may introduce additional considerations. The design team should confirm the appropriate glass specification using the relevant standards, technical evidence and project-specific assessment.

Do not assume that a glass make-up suitable for one elevation is automatically suitable for every part of the building.

5. Address Weather Resistance and Moisture Management

Rainwater control is a fundamental performance requirement for commercial curtain walling in the UK.

The system must manage water at joints, glazing pockets, framing intersections, perimeter seals and connections with adjacent construction. Performance depends on the complete arrangement, not just the quality of an individual seal.

Define air and water performance requirements

The specification should identify the required levels of air permeability, watertightness and resistance to wind loading, using suitable performance criteria and supporting evidence.

These requirements should reflect the building’s exposure and use. Particular attention may be needed around corners, interfaces with roofs and parapets, changes in façade geometry and connections with other external wall materials.

Ask what test evidence is available, what configuration was tested and whether it is representative of the proposed installation. Test results should not be assumed to cover different dimensions, opening arrangements or details unless their applicability has been established.

Coordinate drainage and perimeter interfaces

Many curtain walling systems incorporate drainage routes that allow collected water to move towards designated outlets. These routes need to remain effective after installation and during the building’s service life.

Perimeter details also need careful design. The junction between the curtain wall and the surrounding wall construction must account for weather protection, movement, thermal continuity and appropriate sealing.

For example, a system may perform satisfactorily in isolation but experience problems if an adjacent cladding detail directs water into an unsuitable joint or obstructs drainage.

Drawings should therefore identify the interfaces clearly, with responsibilities for design, installation and inspection agreed between the relevant trades.

6. Coordinate Fire Safety, Acoustic Performance and Ventilation

Curtain wall specifications need to reflect the building’s intended use and the wider design strategy. Fire safety, acoustic separation and ventilation should be considered alongside structural and thermal performance, rather than added as separate checks at the end.

Fire safety and compartment interfaces

The façade design may need to coordinate with compartment floors, internal fire-resisting construction, cavity barriers and perimeter fire-stopping systems.

Requirements depend on the building’s type, height, location, use and applicable regulations. The specification should identify the relevant fire strategy, required performance evidence and responsibilities for coordinating the proposed façade details with the wider building design.

The design team should confirm the applicable fire-safety requirements and technical guidance for the relevant UK nation, alongside advice from appropriately qualified fire-safety professionals.

A fire-resistant component should not be assumed to make the complete façade interface suitable. The performance of the assembled detail and the supporting evidence must be established for the actual application.

Acoustic performance

External noise can affect comfort and the usability of offices, meeting rooms, hotels and other occupied commercial spaces.

The acoustic specification should consider the required internal environment, the surrounding noise exposure, the glazing arrangement, the framing and the interfaces with adjacent construction.

The weakest part of the façade may limit the overall result. Suitable glass alone cannot compensate for poorly coordinated gaps or interfaces.

Opening vents and ventilation

Where opening elements are included, define their purpose and operational requirements. These might relate to occupant comfort, controlled ventilation or the building’s broader mechanical and electrical design.

Coordinate opening locations with internal layouts, furniture, access, cleaning arrangements, control systems and any relevant safety requirements.

A curtain wall window or opening vent should be assessed as part of the complete system, including its weather seals, hardware, maintenance needs and the performance evidence applicable to the selected configuration.

7. Consider Maintenance and Material Selection Early

The most suitable specification is not necessarily the one with the lowest initial purchase cost. It should also consider installation quality, maintenance, component replacement and the expected service conditions of the building.

Plan safe access and future repairs

Large glazed façades can be difficult to maintain if access provisions are considered too late.

Establish how the building will be inspected and cleaned, how drainage routes will be maintained, and how damaged glazing or worn components could be replaced.

The design may need to coordinate with permanent access systems, specialist maintenance equipment, roof arrangements and site-specific safety procedures.

Ask the project team to identify any components that require periodic inspection or specialist attention. The resulting maintenance strategy should reflect the actual system rather than generic assumptions about aluminium façades.

Assess sustainability with evidence

Aluminium is recyclable, but the environmental impact of a curtain wall depends on multiple factors, including material production, recycled content, glazing composition, transport, fabrication, service life and end-of-life treatment.

Where sustainability targets apply, ask for relevant environmental information and establish how the proposed products will contribute to the project’s assessment.

Potential considerations include environmental product declarations, material sourcing information, durability, repairability and the possibility of separating components at the end of their useful life.

Avoid treating recyclability as proof that a complete façade has a low environmental impact. The assessment should use appropriate evidence and the boundaries defined by the project’s sustainability objectives.

For a broader discussion of procurement and environmental considerations, read Fenetek’s guidance on choosing an aluminium curtain wall supplier.

8. Prepare a Specification That Manufacturers and Contractors Can Use

A useful curtain wall specification translates the design intent into information that can be priced, checked, coordinated and delivered.

Vague instructions create room for inconsistent assumptions between the design team, manufacturer and installer. Clear requirements make it easier to identify omissions before they affect procurement or construction.

At a minimum, the specification package should address the following areas.

Specification area	Information to include
Design intent	Elevations, grid dimensions, appearance and framing requirements
System selection	Proposed construction method and applicable system configuration
Structural design	Loads, spans, movement, deflection criteria and fixing requirements
Glazing	Glass make-up, thermal requirements, solar control, acoustics and safety
Weather performance	Air permeability, watertightness and wind-resistance criteria
Fire safety	Relevant interfaces, fire strategy requirements and supporting evidence
Interfaces	Slab edges, perimeter seals, adjacent cladding, doors and opening elements
Installation	Tolerances, access, sequencing, lifting, storage and inspection
Handover	Technical records, maintenance instructions and relevant product documentation

The specification should also establish the approval process for shop drawings, samples, calculations and proposed substitutions.

Where required, a project team may request a representative sample or mock-up to review appearance, interfaces, workmanship and performance-related details. The purpose and acceptance criteria should be agreed in advance.

Assign design responsibilities clearly

Responsibility for different parts of the façade design can sit with different parties. The project documentation should establish who provides the structural calculations, who checks the supporting structure, who coordinates the perimeter interfaces, and who approves glazing and fire-related details.

This is particularly important where a specialist system must fit a structural design developed by a separate consultant.

Before manufacture begins, confirm that the relevant drawings, dimensions, calculations and interfaces have been reviewed through the agreed project process.

For further guidance on programme and site coordination, see professional aluminium curtain wall installation in the UK.

9. Plan Installation and Quality Checks Before Work Begins

Even a well-designed system depends on accurate installation.

Installation planning should start during the design and procurement stages, not after components arrive on site. The contractor and façade specialist need to agree access arrangements, delivery sequences, storage conditions, working areas and installation tolerances.

Before installation, confirm that the supporting structure and fixing locations are suitable, the relevant information has been approved, and any discrepancies have been resolved.

During installation, inspection procedures should address the items identified in the project quality plan. Depending on the system and specification, these may include fixing positions, frame alignment, glazing installation, seals, drainage routes, perimeter details and protection of completed work.

Any testing or inspection should follow the agreed project requirements and relevant technical procedures.

A coordinated installation process also depends on clear communication between the façade contractor and other trades. Late changes to slab edges, cladding, internal fire-stopping or mechanical and electrical services can affect curtain wall interfaces.

Project teams considering a supplier should therefore discuss not only the product, but also the information, coordination and installation arrangements needed to deliver the specified result.

For an overview of curtain wall construction and terminology, readers who need additional background can refer to Fenetek’s article on understanding curtain wall glazing in the UK.

When discussing a proposed system, design requirements or commercial project enquiries with Fenetek, having the latest elevations, approximate dimensions and performance brief available can help establish which technical information is needed next.

Frequently Asked Questions

1. What should be included in an aluminium curtain wall specification?

A specification should define the façade’s structural, thermal, weather, acoustic and safety requirements, alongside glazing details, framing, fixing arrangements, interfaces, installation procedures and maintenance provisions. It should also identify the technical evidence and approvals required for the proposed system.

2. Which aluminium curtain wall system is best for a commercial building?

There is no universal best system. Stick-built and unitised systems suit different combinations of façade geometry, project scale, logistics and programme. The appropriate choice depends on the building design, required performance, site constraints and available technical evidence.

3. How do I compare the thermal performance of curtain wall systems?

Compare equivalent performance measures using the same calculation basis and clearly defined assumptions. Establish whether figures relate to the glass, frame or complete façade element. Also consider thermal bridging, perimeter interfaces, solar gains and the building’s intended internal conditions.

4. Why are thermal breaks important in aluminium curtain walling?

Thermal breaks reduce heat transfer through the aluminium framing by separating parts of the profile with a less conductive material. Their effectiveness depends on the complete frame design, glazing arrangement and interfaces. Overall façade performance should be assessed rather than inferred from the presence of a thermal break alone.

5. What information should be requested from an aluminium curtain walling supplier?

Request relevant system data, configuration limits, thermal information, structural design information, applicable air and water performance evidence, glazing compatibility details and installation guidance. Additional documents may be needed to address fire safety, acoustics, sustainability and project-specific requirements.

6. Do aluminium curtain wall systems need to comply with UK building regulations?

Curtain wall systems must be designed and installed in accordance with the applicable building regulations and other relevant project requirements. The precise obligations depend on the building, its location and the scope of the work. The design team should confirm the relevant requirements and obtain appropriate project-specific advice.

7. What is the difference between curtain wall glazing and a conventional window?

Curtain walling is generally a larger external envelope system attached to the building’s structural frame and assembled from framing, glazing and associated components. A conventional window is usually installed within an opening in a wall. Some curtain wall systems incorporate opening vents, but these do not change the fundamental role of the surrounding façade.

8. When should a curtain wall supplier become involved?

Early involvement is useful once the façade concept, approximate dimensions and performance objectives have been established. It allows the design team to assess system suitability, configuration limits, interfaces, technical information and installation constraints before procurement decisions become difficult to change.

Specify Your Commercial Curtain Wall Project with Confidence

A successful aluminium curtain wall specification connects the building’s architectural intent with verified performance requirements, coordinated technical details and a practical installation strategy. Structural design, glazing, thermal performance, weather protection, fire safety interfaces and maintenance should all be considered as parts of the same building envelope.

For architects, contractors and developers planning a new commercial façade or refurbishment, the next step is to turn these requirements into a project-specific technical brief.

Explore Fenetek Ltd’s aluminium curtain wall systems to review the available system information and discuss the requirements of your project. Sharing the relevant drawings, dimensions and performance objectives can help establish which technical details need to be confirmed before the specification is finalised.