When choosing new windows, you’ll often come across lots of numbers and technical terms: U-values, Part Q, PAS24, air permeability, and more. But what do they all mean? Should it be higher or lower? And how can you tell which windows are the best?
Don’t worry; here’s a simple guide to help you make sense of it all.
Quick Summary: What Performance to Look For
| Category | What to Aim For |
|---|---|
| U-Value | As low as possible (ideally below 1.6 W/m²K for new builds). |
| Acoustic Performance | High decibel reduction (above 35dB for noisy areas). |
| Security | Part Q for new builds, with PAS 24 for additional peace of mind. |
| Air Permeability | Higher = better. Class 4 is the highest. |
| Water Tightness | Higher = better. Class 9A for top performance against heavy rain. |
| Wind Resistance | Higher = better. Class C5 for windows that can withstand the strongest storms. |
1. Thermal Performance: What Are U-Values and Why Do They Matter?
- What is a U-value?
A U-value measures how much heat passes through your window. Think of it as a measure of insulation—the lower the U-value, the better the window is at keeping heat inside your home. - What’s a good U-value?
The current building regulation standard for new builds is a maximum of 1.6 W/m²K. However, many homes, particularly older properties, will not meet this standard without significant upgrades. High-performance windows (like ours!) achieve much better results, with some windows reaching as low as 0.8 W/m²K.
2. Acoustic Performance: How Do Windows Reduce Noise?
- What does acoustic performance measure?
Acoustic performance measures how well a window reduces outside noise, expressed in decibels (dB). - What’s better: higher or lower?
A higher decibel reduction is better. For example, a window with a 39dB reduction (like vacuum-glazed windows) blocks much more noise than one with 30dB. - Ideal situations:
- Living in a busy city? Look for a higher dB rating to keep your home peaceful.
- If you’re in a quieter area, a lower dB rating may be sufficient.
3. Security Testing: What Are Part Q and PAS 24?
- What is Part Q?
Part Q is part of the building regulations for new builds, setting a baseline for security. It ensures windows are designed and installed to resist forced entry attempts. - What is PAS 24?
PAS 24 is an enhanced security standard often used in addition to Part Q. It involves rigorous testing, such as attempts to break into the window using tools, to ensure it provides excellent resistance to intruders. - What do the results mean?
- A window that passes Part Q has met the minimum requirements for security in new builds.
- PAS 24 certification shows the window has undergone even more stringent testing for higher security.
4. Weather Testing: Will Your Windows Keep the Elements Out?
Weather testing ensures your windows can withstand everything the British weather throws at them: wind, rain, and even the occasional storm (though we are in the UK, so read occasional as weekly)!
You will spot a lot of BS here. And no, we don’t mean what ever you think that means! “BS” stands for British Standard, meaning it’s used in the UK. “EN” stands for European Norm, indicating it’s accepted across Europe.
Here’s what you need to know about weather proofing standards:
- Air Permeability (Leakiness):
- Standard: Tested as per BS EN 1026 and classified under BS EN 12207.
- What it measures: The amount of air leakage through closed windows under pressure.
- Optimal performance: Class 4 is the highest rating, indicating minimal air leakage.
- Water Tightness:
- Standard: Tested according to BS EN 1027 and classified under BS EN 12208.
- What it measures: The window’s resistance to water penetration under simulated rain and wind conditions.
- Optimal performance: Class 9A denotes the highest standard for unprotected windows, withstanding water pressure of 600 Pa.
- Wind Resistance:
- Standard: Tested as per BS EN 12211 and classified under BS EN 12210.
- What it measures: The window’s structural integrity under wind pressure.
- Optimal performance: Class C5 represents the highest level of wind resistance, suitable for exposed locations.
Choosing the Right Windows
Now that you know what the letters and numbers mean, you can confidently compare windows and choose the best option for your home. Whether you’re after high thermal performance, superior security, or weather-tight solutions, understanding these terms makes the decision much easier.
Gowercroft Joinery design windows that excel in every category, so you never have to compromise on performance or style. Get in touch with us to learn more!