Timber - PVC - Aluminium - Windows, Doors & Conservatories in Hampshire
Secondary vs. Double Glazing: Cost & Performance Compared
Secondary vs. Double Glazing: Cost & Performance Compared
Category: Buying Guide / Comparisons
Reading Time: 7 Minutes
📌 The Honest Verdict
- For Noise: Secondary Glazing wins (by a large margin).
- For Convenience: Double Glazing wins (easier to open and clean).
- For Heritage: Secondary Glazing wins (preserves the building’s character).
- For Budget: Secondary Glazing is generally cheaper upfront.
It’s the classic renovation dilemma: do you rip out your old windows and start fresh with Double Glazing, or do you keep the originals and install Secondary Glazing behind them?
At KJM, we install both, so we can give you an unbiased answer. The “right” choice depends entirely on why you are upgrading. Are you freezing? Are you kept awake by traffic? Or do you just want lower bills? Let’s compare them head-to-head.
Table of Contents
1. The Difference at a Glance
Double Glazing is a replacement product. We remove your old timber or steel frames entirely and install a new unit (usually uPVC, Aluminium, or Timber) containing two panes of glass separated by a gas-filled spacer bar.
Secondary Glazing is an addition. Your original window stays exactly where it is. We install a slimline aluminium frame with a single pane of glass on the room side of the existing window.
2. Head-to-Head: The 4 Rounds
Performance Battle
Double Glazing
U-Value: ~1.2 W/m²K.
Modern units with Argon gas and warm-edge spacers are incredibly efficient.
Secondary Glazing
U-Value: ~1.8 W/m²K.
Excellent at stopping drafts, but slightly less efficient than a new sealed unit.
🏆 Winner: Double Glazing (Marginally)
Double Glazing
Reduction: ~33dB.
The panes are too close together to stop low-frequency traffic rumble effectively.
Secondary Glazing
Reduction: ~50dB+.
The large 100mm+ air gap acts as a massive shock absorber for sound waves.
🏆 Winner: Secondary Glazing (By a landslide)
Double Glazing
Changes the external look. Often forbidden in Grade II Listed buildings.
Secondary Glazing
Invisible from the street. Preserves original timber. Usually planning-free.
🏆 Winner: Secondary Glazing
3. The Elephant in the Room: Usability
This is where we have to be honest. While secondary glazing wins on noise and heritage, it has a practical drawback: Convenience.
- Opening the Window: To get fresh air, you have to open the secondary unit first, and then open the primary window. It’s a two-step process.
- Cleaning: You now have four glass surfaces to clean instead of two. While secondary panels slide or lift out for access, it is more work than a standard window.
Double Glazing is simpler. One handle, one movement, easy friction hinges for cleaning. If ease of use is your #1 priority, replacement windows win.
4. Cost & Payback
Because secondary glazing involves less material (single pane vs. sealed unit) and much less labour (no ripping out frames, no waste disposal, no plastering), it is significantly cheaper upfront.
| Factor | Double Glazing | Secondary Glazing |
|---|---|---|
| Material Cost | High | Medium |
| Installation Time | 1-2 Days per house | Hours |
| Disruption | Messy (Dust/Plaster) | Clean (Screw-fix only) |
| Relative Price | £££ | ££ |
5. Frequently Asked Questions
Yes. Some homeowners in extremely noisy areas (like near airports) install secondary glazing over modern double glazing. This “Triple Glazing via Secondary” method provides the ultimate acoustic barrier.
It used to. Old systems were bulky and plastic. Modern KJM units are made of powder-coated aluminium with very slim sightlines. When colour-matched to your existing frames, they are barely noticeable.
It depends on the house. In a modern home, new double glazing adds value. In a period property, original features add value. Ripping out original sash windows devalues a heritage home; preserving them with secondary glazing protects that value.
📚 Explore Our Secondary Glazing Hub
Now you’ve compared the options, dive deeper into the specifics:
Mark Pearce is a highly experienced specialist in the double glazing industry, having built his knowledge from the ground up through hands-on experience in installation, manufacturing, sales, and business management. Beyond his role at KJM, Mark is a keen blogger, writer, and traveller, often sharing insights on the latest innovations in the home improvement industry.
- 2026 Design Trends: The 4 Window & Door Styles Defining the Year - 19 December 2025
- The 2026 Glazing Outlook” – High-level summary of the pivot to growth. - 9 December 2025
- Industry News: The Future Homes Standard 2025 & What It Means for Your Windows - 1 December 2025
