Weather Performance & Testing for Architectural Glazing
Protecting your view, whatever the weather
Measuring architectural glazing performance
When designing with architectural glazing, aesthetics and engineering must go hand in hand. For projects incorporating large-format glass doors and windows, ensuring excellent weather performance is critical, not only for occupant comfort and long-term durability, but for meeting regulatory expectations and client satisfaction.
At Cotswold Windows, we work closely with architects and developers to ensure that the systems specified are not only visually striking but technically robust. This means looking beyond surface aesthetics to examine how each glazing system performs under real-world weather conditions.
Why weather performance matters in glazing design
Contemporary architecture often relies on expansive glazed areas to frame views, enhance natural light, and create seamless transitions between indoors and outdoors. But these large openings also bring exposure to the elements – especially in the UK where unpredictable weather patterns driving rain and high winds are common.
Weather testing verifies how well a glazing system can protect a building envelope from air and water ingress, and how it withstands wind pressures. It’s not enough for a system to look good in situ; it must also be proven to perform under pressure – literally.
To make sure our products are up to the job, we focus on three core weather performance indicators:
Water tightness in glazing
Water tightness testing measures a system’s ability to resist water penetration during wind-driven rain.
Why it matters: Water ingress can lead to visible leaks, mould growth, and damage to flooring or interior finishes. In severe cases, it may even affect structural elements or insulation performance.
How it’s tested: Systems are installed into a controlled rig where water is sprayed onto the exterior while internal air pressure is increased incrementally. Testing continues until water breaches the internal seals.
Performance classifications: Based on EN 12208, classifications range from Class 1A to Class 9A. The higher the number, the greater the pressure the system can withstand without leaking. A Class 9A rating means the system has been tested to the highest standard for water resistance.
What we recommend: Systems like Sky-Frame Frameless Windows & Doors and MHB Steel Windows & Doors have achieved class-leading ratings, with Sky-Frame reaching up to Class 9A. This makes them suitable for even exposed or coastal applications, where water resistance is non-negotiable.
Air permeability in glazing
This measures the amount of air that leaks through the system when exposed to pressure differences across the glazing. However, it’s important to note that some air permeability is essential to maintain comfortable airflow within a building.
Why it matters: Excess air leakage can compromise energy efficiency, cause drafts, and reduce the effectiveness of heating or cooling systems. Good air tightness is essential for meeting thermal performance standards.
How it’s tested: Following EN 12207, systems are exposed to increasing internal and external pressures while sensors measure air flow.
Performance classifications: Performance is categorised from Class 1 to Class 4Class 4 is the highest level of performance, indicating extremely low air leakage. .
What we recommend: Both Sky-Frame and MHB achieve Class 4 for air permeability. This ensures that even with large openings, the thermal envelope of the building remains uncompromised.
Resistance to wind loading in glazing
Wind load testing evaluates how much pressure from wind a glazing system can resist without permanent deformation, damage, or failure.
Why it matters: Resisting high wind loads is essential to structural safety, particularly in tall or exposed buildings. Flexing or bowing of frames or glass can lead to component failure, seal breach, or rattling in service.
How it’s tested: Systems are subjected to positive and negative pressures in a test rig, simulating wind blowing both into and out of the building. Measurements are taken for both elastic deformation and residual displacement.
Performance Classifications: As per EN 12210, classes range from A1 (lowest) to C5 (highest). C5-rated systems are suitable for the most demanding environments, including high-rise or coastal properties.
What we recommend: Sky-Frame has been tested under hurricane conditions in the US, with independent assessments to Miami-Dade standards. MHB Steel also offers exceptional rigidity, with ratings including C5 wind load resistance.
Weather tested glazing you can count on
When comparing glazing system performances, it’s easy to be impressed by the figures in a brochure. But just like fuel economy ratings on a car, those numbers often reflect ideal conditions in controlled environments – not the reality of day-to-day use with architectural glazing systems in large formats.
Many systems perform well when tested at standard sizes, but their performance drops off quickly when scaled up to larger openings. With premium systems like Sky-Frame, that’s not a concern. They have been tested well beyond the typical sizes – up to 20 metres wide in some cases – so you can have full confidence that they will still perform when used in extra-large formats.
What’s more, both Sky-Frame and MHB operate their own in-house test rigs. This allows them to rigorously develop and assess their systems, simulating extreme weather scenarios and fine-tuning performance over time. They’re not limited to one-off tests at commercial laboratories – they can push their systems harder and more often, ensuring continuous improvement.
Declaration of Performance: what architects need to know
Under UK building regulations and CE/UKCA marking requirements, manufacturers must provide a Declaration of Performance (DoP) for their systems. This document outlines certified glazing system performance ratings for thermal insulation, safety, weather resistance, and more.
However, it’s important to note that the DoP only applies up to the maximum tested size. If a product is used beyond its certified dimensions, it may technically be non-compliant – even if the visual design appears similar.
By specifying products such as Sky-Frame frameless windows and doors and MHB Steel windows and doors that are rigorously tested beyond industry standards, we help architects and developers achieve the desired design aesthetic with practical application.
Trusted systems for demanding projects
We only specify products that deliver and Sky-Frame and MHB Steel are two of the best-performing architectural glazing systems on the market.
Our role at Cotswold Windows is to bring clarity to complex decisions. We offer expert insight into not just how systems look, but how they perform when it matters. So, if you’re working on a project that needs weather tested glazing, get in touch with us and we’ll help you choose, design and install the best product for the job.
