Curtain walling and Building Regulations: what you need to know

Curtain walling is widely used in commercial and high-end residential projects, especially those offering multi-occupancy. But what is curtain walling, precisely, and how does it differ from other glazing systems?

The Centre for Window Cladding and Technology (CWCT) defines curtain walling as: "A form of vertical building enclosure which supports no load other than its own weight, that of ancillary components and the environmental forces which act upon it."1 In other words, curtain walling is a non-load-bearing facade system that is designed to withstand harsh weather conditions and its own weight. Being structurally independent of the rest of the building is the key difference between curtain walling and other glazing systems.

Typically, curtain walling combines a metal frame – most often aluminium – with large areas of glazing, and other materials can be incorporated. There are many different types of curtain walling, with the two main types being:

• Stick systems – Supplied as individual mullions and transoms (the “sticks”) that are assembled on site. The glazing is installed and sealed once the framework is complete.
• Unitised systems – Prefabricated in panels off-site and delivered ready for installation. They are lifted into place for quicker installation and consistent quality.

Solarlux SL Modular Facades are a type of unitised curtain walling. Justin Spires, technical lead at Solarlux, explains that these storey-height aluminium framed units are precision-engineered for quality and consistency. “Our factory-assembled approach minimises on-site installation time and risk. It helps to ensure that the completed project achieves the requirements of the Building Regulations and other standards, while also providing an attractive finish,” he explains, adding: “The result is a facade that performs as well as it looks.”

1 https://www.cwct.co.uk/pages/facets#!articles/1222-9018-0301-construction
https://crucialengineering.co.uk/blog/what-is-curtain-walling/

Building regulations are devolved across the UK, meaning that each nation issues its own guidance:

• England: Building Regulations 2010 – Approved Documents
• Wales: Building Regulations 2010 (as amended for Wales) – Approved Documents
• Scotland: Building (Scotland) Regulations 2004 – Technical Handbooks
• Northern Ireland: Building Regulations (Northern Ireland) 2012 – Technical Booklets

While the core performance principles for curtain walling – such as thermal efficiency, weather resistance, structural stability and safety – are shared across the devolved nations, the details for compliance differ. It’s therefore essential to consult the relevant guidance for your location to ensure the finished facade achieves compliance.

Listed below is the key guidance under the Building Regulations for England, set out in their corresponding Approved Documents.

Part L of the Building Regulations sets out the requirements for the energy efficiency of buildings. Compliance with Part L for curtain walls centres on achieving the necessary thermal performance – measured by U-values.

A U-value is the measure of thermal transmittance – that is, how easily heat travels through the building fabric, with lower values meaning better performance. It’s important to note that U-values look at a whole building element, rather than the individual components, so it’s the entire build-up that matters. For a curtain wall system, this means the frame and glazing, thermal breaks,
installation detailing and any other components that make up the facade.

Approved Document L is split into two volumes:

● Volume 1 for dwellings
● Volume 2 for buildings other than dwellings.

Both volumes set maximum (limiting) U-values for building elements, including windows, glazed doors and curtain walling in new-build and refurbishment projects. For new build dwellings, notional U-values provide a benchmark for compliance modelling. Designers usually aim to match or improve upon the notional figures to achieve overall energy targets.
 

In addition to achieving the required U-values, curtain walling should also contribute to the building envelope’s air tightness. For new builds and major refurbishments, Approved Document L requires air-permeability testing, which is typically conducted in accordance with CIBSE (Chartered Institution of Building Services Engineers) TM23.

Compliance with Approved Document L is assessed using the Standard Assessment Procedure (SAP) for dwellings and the Simplified Building Energy Model (SBEM) for buildings other than dwellings. These calculate energy performance based on a combination of building fabric efficiency, heating systems, lighting and the use of renewable technologies.

The most recent update to Part L, published in 2021 with amendments in 2022, introduced stricter U-value limits as part of an interim uplift towards the Future Homes Standard (FHS) and the Future Buildings Standard (FBS). These upcoming standards – expected in autumn 2025 – will set even tighter energy efficiency targets for all new buildings from 2027.

Fire safety is a critical consideration for all buildings. Approved Document B provides extensive guidance for fire safety, covering issues ranging from building materials and compartmentation through to signage, warning systems and access for firefighters.

For curtain walls, UK fire regulations include fire-stopping measures, means of escape, effective compartmentation using cavity barriers and the fire performance of the materials – including reaction to fire, smoke production and the behaviour of burning droplets.

Approved Document B is split into two volumes: Volume 1 for dwellings and Volume 2 for buildings other than dwellings. In multi-occupancy or mixed-use developments, both volumes may be relevant and should be consulted to ensure compliance across all parts of the building.

Curtain wall systems in relevant buildings must meet the combustibility requirements of Regulation 7(2) – external wall components must achieve an A1 or A2-s1,d0 classification under BS EN 13501-1. Where fire resistance is required, systems are tested in accordance with BS EN 1364-3 or BS EN1364-4 to ensure that integrity is maintained for the specified duration.

Part K aims to improve safety for building users. For balcony curtain walling, key considerations include:

• Glazing specification – Part K does not mandate specific glass types, but using toughened or laminated glass can help to achieve the required impact resistance.
• Impact resistance – Glazing performance is typically tested to BS EN 12600, which classifies glass based on pendulum impact tests. This helps determine suitability in critical locations, such as below 800mm from finished floor level.
• Structural performance – Where curtain walling encloses a balcony, it effectively serves as a balustrade. Compliance with BS 6180:2011 ensures that the glass, frame and fixings can resist the vertical and horizontal loads imposed by users.
• Minimum height – Approved Document K requires balcony guardings to have a minimum height of 1100mm above any adjacent surface accessible to a person.

Part M focuses on inclusive access. It helps to ensure that buildings are safe and usable for everyone, including people with limited mobility. For balcony curtain walling, this mainly relates to any operable panels or windows:

• Operable panels and windows should have handles and locks that are easily accessible and usable by people of varying heights and abilities, including seated users. This typically means 750–1200mm above finished floor level.
• Panels should be easy to operate, requiring minimal force to open or close.

Approved Document F sets out the requirements for adequate ventilation in buildings, helping to create a healthy and comfortable indoor environment, while preventing issues such as condensation, mould and poor indoor air quality.

To comply with Part F, curtain walling systems should provide adequate ventilation. This can include:

Integrated ventilation: Including trickle ventilators within the curtain walling frame for background ventilation.

• Operable openings: Installing openable windows or panels for purge ventilation.
• Mechanical ventilation: Implementing mechanical systems where natural ventilation is insufficient.

Typical background ventilation rates are around 5,000 mm² equivalent area per habitable room in dwellings and approximately 10 litres per second per person in offices. However, these values may vary depending on the specific room or building requirements.

In addition to the Building Regulations, other performance requirements should be considered when specifying curtain walling, including:

• BS 8233:2014 – Provides guidance for acceptable internal noise levels from external sources, such as traffic.
• BS EN 13830 – Is the UK and European standard for curtain walling products. It sets out requirements for design, testing and performance, helping to ensure that curtain wall systems meet expected levels of structural strength, weather resistance and thermal and acoustic performance.
• BS EN 12155 and BS EN 12154 – Are standards for testing the water tightness of curtain walling.

Justin explains that various industry bodies have also issued best-practice guidance. “While compliance with documents such as the CWCT and NHBC Standards is not legally required, it provides confidence that the curtain wall system will deliver the required performance in terms of structural integrity, weather resistance and thermal efficiency,” he says. “Installing curtain walling that achieves these standards can also help to mitigate damage claims and regulatory challenges,” he adds.

Solarlux curtain wall systems are designed to provide thermal efficiency, weather protection and safety, while maximising natural light and the sense of space. Manufactured and tested to meet both UK building regulations and European standards, they combine precision-engineered aluminium frames with high-performance glazing options – including TSG (Toughened Safety Glass), TSG-H (Toughened Safety Glass-Heat Soak Tested) and LSG (Laminated Safety Glass) – with up to 30dB of
sound reduction for non-insulated systems and 46dB for insulated systems.

Justin notes that the Solarlux SL Modular system combines balcony balustrades and glazing into a single prefabricated unit, reducing on-site assembly time and ensuring consistent performance. He adds that a variety of customisation options are available: “The system is available in insulated and non-insulated versions, it can be adjusted to suit new-build and retrofit projects, and clients can choose from a wide range of aluminium frame colours too.”

Solarlux curtain walling provides architects, contractors and building owners with flexible curtain walling that balances aesthetics and regulatory compliance.