How Different Window Systems Perform in British Weather
November
27
2025
How Different Window Systems Perform in British Weather: A Complete Comparison
Choosing the right window system can make a dramatic difference to the comfort, efficiency, and longevity of your home — especially in the UK, where weather conditions can range from coastal salt exposure and driving rain to inland storms and high winds.
In this article, we compare the performance of the UK’s most common window types:
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UPVC double glazed
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Typical aluminium double glazed
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Aluminium-clad timber systems (e.g., Rationel & Velfac)
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Premium European systems (e.g., Internorm)
This helps homeowners, architects, and self-builders understand what each system offers in real-world British weather.
🌬 1. Air Permeability — Draught-Proofing & Airtightness
Air permeability measures how much air can pass through the closed window. The higher the pressure rating, the better the performance.
Comparison
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Aluminium-clad timber systems – ~600 Pa
Very airtight, good for exposed sites.
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Premium European systems – 600–900 Pa
Among the best airtightness available.
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Typical aluminium – 300–450 Pa
Mid-range performance.
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Typical UPVC – ~300 Pa (Class 3)
Meets the basic UK requirement but allows more draught transfer.
👉 Aluminium-clad timber and premium systems offer around double the airtightness of standard UPVC and aluminium frames.
🌪 2. Wind Resistance — Frame Strength in Storm Conditions
Wind resistance shows how well the structure holds up under high wind pressure — vital in exposed, coastal, or elevated areas.
Comparison
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Aluminium-clad timber systems – ~1600 Pa
Very strong and stable under load.
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Premium European systems – 2000–2400 Pa
Some of the strongest residential windows available.
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Typical aluminium – 1200–1600 Pa
Good rigidity and stability.
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Typical UPVC – 800–1200 Pa
Adequate for sheltered areas, but frames can flex in storms.
👉 Aluminium and alu-clad timber systems significantly outperform UPVC in structural stability.
🌧 3. Water Tightness — Protection Against Driving Rain
Water tightness indicates how well the window prevents wind-driven rain from penetrating the frame or seals.
Comparison
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Aluminium-clad timber systems – ~600 Pa
Excellent resistance to severe wind-driven rain.
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Premium European systems – 600–900 Pa
Best-in-class moisture protection.
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Typical aluminium – 300–450 Pa
Suitable for most regions.
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Typical UPVC – 200–300 Pa
Meets British Standards but less resilient in storms.
👉 The higher-end systems offer 2–3× the water-tightness of basic UPVC systems.
🔧 4. Operational Cycles — Hardware Longevity
Operational cycle testing simulates years of opening and closing to measure how long the mechanism lasts before wearing down.
Comparison
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Premium European systems – 20,000+ cycles
Exceptional durability.
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Aluminium-clad timber systems – 10,000–20,000 cycles
Strong, long-lasting hardware.
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Typical aluminium – 7,000–10,000 cycles
A solid mid-range performer.
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Typical UPVC – ~5,000 cycles
Hardware wears faster with use.
👉 Higher-end systems last 2–4× longer than typical UPVC hardware.
🏡 Which Window System Performs Best Overall?
Best for exposed or coastal homes
Best for general UK homes
Most cost-effective
Highest performance category
🌦 Overall Ranking in Harsh British Weather
From strongest to most basic:
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Premium European composite systems
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Aluminium-clad timber systems
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Typical aluminium double glazed systems
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Typical UPVC double glazed systems
💡 Key Takeaway
While all systems sold in the UK meet minimum requirements, there is a significant performance gap between entry-level UPVC and higher-end aluminium or composite systems — especially in airtightness, storm resistance, and long-term durability.
This means choosing the right system depends on: