By the Letter – Specifying Compliant Fenestration Systems

Fenestration is an important part of the building envelope and one that needs careful consideration to ensure that aesthetic appeal is carefully balanced with increasingly stringent performance requirements. Andrew Cooper, National Specification Manager from Senior Architectural Systems, one of the UK’s largest privately-owned manufacturers of aluminium windows, doors and curtain wall solutions, provides a checklist for compliance and how early engagement can help.


Putting Part L first

The recent changes to Part L of the Building Regulations have signalled a huge change for manufacturers and specifiers alike, with new lower U-value targets for windows and glazed doors introduced in June 2022 and made mandatory for all new buildings from June 2023. As the updates to Part L also apply to glazed facades in commercial projects, the first consideration for any specified fenestration systems must be its U-values and thermal performance. But is less always more? It’s important not to take any quoted U-values at face value but to view them in the context of both operational and embodied carbon. Is the system fully recyclable? Is the manufacturing process energy intensive, and is the carbon footprint around transportation a concern? Aluminium systems can often provide the solution as products, such as those manufactured by Senior, offer cradle-to-cradle recyclability and exceptional durability. Choosing a UK-based manufacturer will also limit the amount of mileage and carbon generated through the distribution and delivery of products.

Don’t overlook Part O

Reducing heat loss from the building fabric has to be balanced alongside the need to reduce overheating, and the recent changes to Part O of the Building Regulations also apply to the specification of doors and windows in new buildings. Here, design flexibility is key as the size and number of windows permitted in a room are affected by the direction they face and the ratio of the floor space. The use of slim aluminium frames can enhance the permitted glazing elements, and by working with a supplier that can offer low-U-value systems in a wide range of sizes and configurations, more innovative layouts can be considered. This, in turn, allows the risk of overheating to be addressed without having to compromise on the beneficial effects of daylighting and the aesthetic appeal of glazing.

Making Part F a breeze

The challenge of reducing heat loss through doors and windows, while preventing overheating, must also be viewed in the context of Part F. This document advises on good ventilation strategies, to boost wellbeing but also to manage the risk of condensation build up, which is a major issue for many homes across the UK. Unless there is another suitable form of ventilation within the room, window systems should incorporate trickle vents to enable continuous and secure background ventilation. Bear in mind that trickle vents will affect the U-value performance of a window, so always be sure to push your supplier to provide the most accurate thermal calculations from the offset.

The very nature of windows means that, of course, they can be opened for ventilation, but here, safety and security must be considered. One popular solution within high-rise housing developments is the use of parallel push windows. With hinges on all sides of the frame, the window can be easily pushed open and yet will remain parallel to the wall. This enables rooms to be safely ventilated, with the limited opening helping to reduce the risk of falls from the window.

Safety and security for all

As well as safety, security is an important part of the specification process, particularly for residential projects. Part Q compliance is required for any accessible window or door, whether this is at ground-floor level or above roofs and balconies. Many products will also be accredited to PAS 24 or Secured by Design, and although these are both great benchmarks for the security of the system, neither is a guarantee of meeting the requirements of Part Q. So, it’s important to have these discussions early on in the design process.

Ensuring the safety of occupants within a building is vitally important. This is reflected in both Part B of the Building Regulations and the new Fire Safety Act, which covers the risk to high-rise buildings in more detail. The layout of doors and windows to provide a suitable means of evacuation is a key consideration, as is the use of fire-rated doors. Again, this should be addressed at the earliest possible stage to ensure that the specified fenestration systems can safely tick all the boxes.

Raising standards in 2024 and beyond

The 2022 and 2023 changes to Part L are a forerunner to the Future Homes Standard that is expected to come into force in 2025 and will see energy-saving targets tightened even further. For windows and doors, this will likely require greater use of triple glazing as a way to support the already impressive thermal efficiency of the aluminium frame. For contractors, the new changes mean a greater focus on the installation process to ensure that the specified products work as intended to improve the overall energy efficiency of a build. Photographic evidence is already required for Part L compliance, but to bridge this ‘performance gap’, we must first address the ‘skills gap’ that is widening every year. There is no quick fix here, but close collaboration with manufacturers to receive hands-on training in the fabrication and installation of these compliant fenestration systems can help.

Supply chain collaboration is undoubtedly the most effective solution to making the specification of more innovative and sustainable products more efficient for all.

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