Timber - PVC - Aluminium - Windows, Doors & Conservatories in Hampshire

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.

1. The Difference at a Glance
2. Head-to-Head: The 4 Rounds
3. The Elephant in the Room: Usability
4. Cost & Payback
5. Frequently Asked Questions

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

Round 1: Heat Retention

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)

Round 2: Noise Reduction

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)

Round 3: Aesthetics & Planning

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

Cross section comparison of secondary versus double glazing showing air gaps

The massive air gap in secondary glazing is what makes it superior for noise reduction.

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	£££	££

💡 KJM Pro Tip: If your original frames are rotting, secondary glazing is a false economy. You must repair the primary window first. However, if your frames are sound, secondary glazing offers a faster “Return on Investment” via energy savings.

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:

🔊 Noise Guide: Why Secondary Wins 💧 Condensation: Stop wet windows 🏠 View Range: See our styles 🆚 Comparison: You are here 🏛️ Listed Buildings: Planning rules 📖 Overview: All Benefits Explained

Still undecided? Contact KJM for free, impartial advice.

About
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Mark Pearce

With over four decades in the glazing industry, Mark Pearce has been at the heart of KJM Windows & Conservatories since 1983. Starting as a building labourer, he quickly rose through the ranks, working as a window and door installer from 1984, a factory operator manufacturing windows later that year, factory manager in 1992, and joining the sales team in 1994. Becoming a Director in 2002, and finally, the sole owner in 2010, Mark Pearce is truly a double glazing expert and has led KJM to become a leading supplier of high-quality windows, doors, and conservatories across Andover and the South of England.

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.

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Timber - PVC - Aluminium - Windows, Doors & Conservatories in Hampshire

Secondary vs. Double Glazing: Cost & Performance Compared